Spegnere il fuoco con onde sonore (a bassa frequenza)

March 30, 2015 in Uncategorized

Due studenti di ingegneria dell’universita’ della George Mason Univerisity, hanno realizzato un
dispositivo che spegne il fuoco usando onde sonore a bassa frequenza, in particolare per i test con l’alcol denaturato e’ stata usata una frequenza fra 30 e 60 mhz. Non sono i primi ad osservare questo fenomeno si veda per esempio il video pubblicato da Scientific American sul suo sito di un esperimento fatto usando della musica da Dmitriy Plaks della University of West Georgia, ma sono i primi a realizzare un dispositivo per lo spegnimento del fuoco tramite onde sonore.

Per vedere un video della dimostrazione potete andare, per esempio, al sito del Washington Post

When it comes to putting out fire, GMU students show it’s all about that bass

It happens so quickly you almost don’t believe it: Seth Robertson and Viet Tran ignite a fire, snap on their low-rumbling bass frequency generator and extinguish the flames in seconds. And even after you’ve seen it over and over, it’s still unbelievable.

But the two senior engineering majors at George Mason University appear to have invented and built a way to use sound waves to put out fires. It started as an idea for a senior research project, and after a year of trial and error and spending about $600 of their own money, they have built a somewhat portable sound generator, amplifier, power source and focusing tube that would seem to have great potential in attacking fires in a variety of situations.

Robertson, 23, and Tran, 28, applied for a provisional patent at the end of November, which gives them a year to do further testing on other flammable chemicals — so far they have put out only fires started with rubbing alcohol — and to continue to refine their device. Although they originally conceived of the device as a way to put out kitchen fires and, perhaps, fires in spacecraft, a local fire department already has asked them to test their bass waves on a structure fire; they think the concept could replace the toxic and messy chemicals involved in fire extinguishers.

Robertson of Newport News, Va., and Tran of Arlington, Va., are electrical and computer engineering majors, and the idea for their senior project came about only because they didn’t like the ideas that their professors had proposed. They had seen research on how sound waves could disrupt flames, “but there’s nothing on the market that works,” Robertson said. “So we thought we could be the ones to make it happen. And that’s the inspiration for the project.”

As with all great scientific inspiration, there were plenty of naysayers, the pair said. They are electrical engineers, not chemical, and were told, “You guys don’t know what you’re talking about,” Tran said. A number of faculty members declined to serve as advisers on the project, but professor Brian Mark agreed to oversee it and not fail them if the whole thing flopped, Tran said.

But how does it work? The basic concept, Tran said, is that sound waves are also “pressure waves, and they displace some of the oxygen” as they travel through the air. Oxygen, we all recall from high school chemistry, fuels fire. At a certain frequency, the sound waves “separate the oxygen [in the fire] from the fuel. The pressure wave is going back and forth, and that agitates where the air is. That specific space is enough to keep the fire from reigniting.”

So the trial-and-error began. They placed flaming rubbing alcohol next to a large subwoofer and found that it wasn’t necessarily all about that bass, musically speaking, at least. “Music isn’t really good,” Robertson said, “because it doesn’t stay consistent.”

They tried ultra-high frequencies, such as 20,000 or 30,000 hertz, and could see the flames vibrating but not going out. They took it down low, and at the range of 30 to 60 hertz, the fires began to extinguish.

“I honestly didn’t think it would work as well as it did,” Tran said.

But the goal was to create something portable and affordable like a fire extinguisher that would generate the sound wave at the correct frequency, which they were able to do with the help of an oscilloscope that measured the waves.

They connected their frequency generator to a small amplifier and linked the amplifier to a small electric power source. These are hooked up to a collimator that they made out of a large cardboard tube with a hole at the end, which narrows the sound waves to a smaller area.

And it worked.

“My initial impression was that it wouldn’t work,” Mark, their adviser, said. “Some students take the safe path, but Viet and Seth took the higher-risk option.”

Both are set to graduate in May. Robertson has been working at the Defense Department and has been offered a job with the Air Force. Tran has interned at a Dulles, Va.-area aerospace firm with a promise of a job after graduation.

Although the students originally envisioned their device as a tool to attack kitchen fires and to eliminate the toxic monoammonium phosphate used in commercial fire extinguishers, they can see more uses: in confined areas in space, or wide areas outdoors, such as forest fires. Not having to use water or foam would be a bonus in many situations.

“We still want to do a lot more testing,” Tran said, “to see if we need to change the frequency [to extinguish] other” materials, before plunking down thousands of dollars to apply for a patent.

In 2012, the Defense Advanced Research Projects Agency conducted a project on “acoustic suppression of flame” and found that it worked on small levels but could not determine if it would work at “the levels required for defense applications,” the agency said.

Kenneth E. Isman, a clinical professor in the University of Maryland’s fire-protection engineering department, said that the question of scale is important. “It’s one thing to put out a tiny fire in a pan,” Isman said. “But how much power would you need to deal with a couch or bed on fire, which is a common scenario in deadly fires?”

The project also would have to address different types of fires — solid combustibles such as wood, paper or metals, or electrical equipment — and keep a fire from reigniting.

“One of the problems with sound waves is that they do not cool the fuel,” Isman said. “So even if you get the fire out, it will rekindle if you don’t either take away the fuel or cool it.”

Eclissi del 20 Marzo

March 19, 2015 in formulas, mathematics, news, physics

da webusers.fis.uniroma3.it

–> Puoi collegarti  e osservarla in diretta dall’Astrogarden (streaming) <–

Il 20 Marzo 2015 sarà possibile osservare un’eclissi di Sole dal nostro emisfero. L’eclissi sarà totale nella zona dell’Atlantico settentrionale (Isole Fær Øer e Isole Svalbard), mentre in Italia il disco solare verrà oscurato solo in parte e la percentuale di questa copertura dipenderà dalla latitudine dell’osservatore.

immagine1A Roma, e quindi anche dal nostro Astrogarden, vedremo che la Luna inizierà a coprire il Sole alle 9:24 di mattina con il raggiungimento dell’oscuramento massimo (≈ 62%) previsto tra le 10:30 e le 10:40. Il fenomeno si concluderà alle 11:43, con l’uscita definitiva del nostro satellite dal disco solare.
Questi tempi variano di qualche minuto a seconda delle località italiane da dove si osserva l’eclissi, così come varia la percentuale di oscuramento. Per esempio a Milano, l’eclissi sarà osservabile con una copertura massima pari al 68% del diametro apparente del Sole, mentre a Palermo non si supererà il 50%.



Come osservare l’eclissi

Non osservare mai il Sole ad occhio nudo o con qualche strumento ottico (binocoli o telescopi) senza una protezione per gli occhi. Gli occhiali da Sole non sono una protezione! Il rischio è quello di danneggiare in modo permanente la vista.

Per osservare il Sole, anche durante l’eclissi, è indispensabile munirsi di strumenti appositi. Una camera stenopeica può costituire un buon metodo per proiettare l’immagine solare. Per l’osservazione diretta ci sono molti metodi “artigianali”, come gli occhiali da saldatore, vetri anneriti, pellicole di Mylar. Questi metodi vanno bene per l’osservazione occasionale, ma costituiscono tutti metodi NON CERTIFICATI in quanto, soprattutto nel caso di osservazione prolungata, non garantiscono una protezione completa a tutte le lunghezze d’onda. L’unico sistema sicuro è quello di utilizzare una particolare pellicola, il Filtro solare Baader AstroSolar, certificato CE, acquistabile anche in rete da rivenditori specializzati. Esistono in commercio a prezzi molto contenuti, speciali occhiali realizzati con questo filtro. Un altro sistema è quello di seguire dirette streaming, come quella che trasmetteremo dall’Astrogarden, con il telescopio del Dipartimento di Matematica e Fisica di Roma Tre.

  •  Come costruire una camera stenopeica per osservare il Sole (video)
  • Per saperne di più su una camera stenopeica per osservare il Sole (video)

Gli occhiali da saldatore possono essere trovati nei negozio di ferramenta o per materiali antinfortunistici, mentre è possibile acquistare filtri Mylar a un piccolo prezzo nei negozi di ottica sotto forma di appositi occhialini certificati per eclissi. Tali filtri lasciano passare solo lo 0.003% della luce visibile e lo 0.5% della radiazione infrarossa e ci permettono di osservare l’eclissi senza rischio di danneggiare il nostro occhio.

I nostri occhi (o meglio il sistema di lenti che li compone) concentrano la luce del Sole e la focalizzano tutta in un punto della retina. Guardare il Sole può causare danni permanenti agli occhi (anche cecità). Un’eccessiva esposizione può provocare danni anche dopo alcune ore in quanto le terminazioni nervose attorno alla retina sono poche e quindi non si avverte subito la sensazione di dolore.

Dove osservare l’eclissi del 20 marzo

  •  Puoi collegarti qui e osservarla in diretta dall’Astrogarden (streaming).
  • L’Agenzia Regionale per i Parchi, il Dipartimento di Matematica e Fisica dell’Università Roma Tre e il Parco dell’Appia Antica organizzano una mattinata ad osservare l’eclisse. Appuntamento in Via Appia Antica 42/50 ore 9:00.  (locandina)



Il fenomeno dell’eclissi, parola che deriva dal greco ἔκ (ek) e λείπειν (leipein) e che sta a significare “allontanarsi da”, “nascondersi”, “rendersi invisibile”, è un evento astronomico che implica l’oscuramento parziale o totale di un corpo celeste a causa dell’interposizione di uno, o più corpi celesti, tra esso e una fonte luminosa. In altre parole parliamo di un allineamento di 3 o più corpi celesti sullo stesso piano. Il sistema di nostro interesse è il sistema Sole-Terra-Luna e nel suo ambito avvengono, e sono quindi oggetto di studio, due tipi di eclissi: eclissi di Luna ed eclissi di Sole. Il piano dell’orbita lunare è inclinato, di un angolo di circa 5°, rispetto al piano dell’eclittica (il piano orbitale del Sole relativo al punto di vista terrestre), quindi anche se la Luna impiega poco meno di un mese per completare un giro intorno alla Terra (la durata del mese ha proprio origine dal ciclo lunare), l’allineamento Sole-Terra-Luna non si verifica sempre. Affinchè si verifichi l’allineamento la Luna deve trovarsi nel piano dell’eclittica (cosa che avviene due volte per ogni orbita lunare) proprio durante la fase di Luna Piena (eclissi di Luna) o Luna Nuova (eclissi di Sole).


Eclissi di Luna

immagine2Le eclissi di Luna avvengono quando il cono d’ombra terreste investe in maniera “totale” o “parziale” il globo Lunare. Questo tipo di fenomeno può avvenire solo quando la Luna ed il Sole si trovano in due punti diametralmente opposti rispetto alla Terra (fase di plenilunio), ossia quando la Luna si trova in vicinanza di uno dei nodi della sua orbita.

Un’eclissi totale di Luna ha durata massima di 1h e 40 min: per effetto dell’atmosfera terrestre i raggi solari vengono in parte diffusi e in parte rifratti verso l’interno del cono d’ombra, questo fa si che la Luna in eclissi totale continui ad essere più o meno visibile (questo tempo di visibilità dipende dalla sua distanza dall’asse del cono d’ombra) assumendo una colorazione tipica sui toni del rosso rame.

Questo tipo di eclissi è visibile da tutte le località terrestri per le quali il nostro satellite si trova al di sopra dell’orizzonte.

Questi fenomeni non avvengono molto spesso come ci si aspetterebbe in quanto il piano di rivoluzione della Luna è inclinato rispetto all’eclittica, questo fa sì che l’eclissi non avvenga ogni novilunio ma solo 4-5 volte l’anno.




Eclissi di Sole

Il fenomeno delle eclissi solare avviene a causa dell’interposizione della Luna fra la Terra ed il Sole, il cui disco luminoso viene quindi coperto interamente o in parte, dando luogo ad eclissi totali o parziali. Questo tipo di eclissi avviene, quindi, solo al momento della congiunzione della Luna con il Sole, cioè al novilunio, quando la Luna si trova in prossimità di uno dei nodi. A causa delle diverse distanze della Terra dal Sole e dalla Luna e delle loro diverse dimensioni, la Terra non riesce mai ad entrare interamente nel cono d’ombra lunare (la Luna è il corpo più piccolo tra i tre). Questo comporta che un’eclissi di Sole riguarda unicamente una parte limitata della superficie terrestre: Si avranno zone d’ombra in cui l’eclissi sarà totale e zone di penombra in cui l’eclissi sarà parziale. L’eclissi apparirà totale solo in una zona ristretta della Terra: l’ombra della Luna si muove sulla superficie terrestre a causa del moto di rotazione del nostro pianeta descrivendo una fascia, larga poco più di 200 km. In un’eclissi totale il disco Lunare copre interamente, ed in maniera quasi esatta, il disco solare: ciò è dovuto al fatto che il diametro angolare apparente dei due astri è pressoché uguale. Il completo ricoprimento del Sole si ha se, verificate le condizioni di distanza relativa elencate fino ad ora, il diametro angolare della Luna è uguale o maggiore di quello del Sole. Quando l’eclissi totale si verifica con la Luna all’apogeo, quindi con diametro angolare minore di quello del Sole, il ricoprimento non può essere totale: si ha una cosiddetta eclissi “anulare”.

Qualche istante prima di un’eclissi totale possono essere osservate sul fondo solare le perle di Baily, serie di piccoli punti neri, che sottolineano l’irregolarità del bordo Lunare. Nel momento della totalità appaiono la corona, i pennacchi coronali e le protuberanze solari. Sono, inoltre visibili i pianeti e le stelle più luminose.

 Appuntamenti passati

Eventi di questo tipo non avvenivano in Italia dal 4 Gennaio 2011, data in cui avvenne un’eclissi parziale molto singolare: quella mattina il Sole sorse sull’Europa già eclissato. Sempre nel 2011, il 15 Giugno, ebbe luogo un’eclissi Lunare visibile dall’Italia a partire dalle ore 21:25: la Luna quella sera sorse pochi minuti prima a totalità già iniziata. L’ultima eclissi solare totale visibile dall’Italia è avvenuta il 15 febbraio 1961.

I prossimi appuntamenti

Nel nostro Paese la prossima eclissi solare parziale degna di nota sarà il 25 ottobre 2022, con un oscuramento parziale del 27% circa. La prossima eclissi Lunare invece, si verificherà il 28 settembre 2015 con il raggiungimento del totale oscuramento del disco Lunare intorno alle ore 4:00 del mattino e anche in quel caso sarà un appuntamento da non perdere.

La prossima eclissi totale che lambirà il territorio italiano (Lampedusa) avverrà il 2 agosto del 2027. Ma per osservare la prossima vera e propria eclissi solare totale “italiana” bisognerà attendere i 6 luglio del 2187…  Ma, niente paura, ci sono almeno un paio di eclissi solari l’anno ed è sempre possibile organizzare un bel viaggio. Ecco un piccolo elenco delle prossime eclissi solari totali: 9 marzo 2016, Sumatra, Borneo; 21 agosto 2017, USA; 14 dicembre 2020, Argentina.


Fenomeni astronomici come le eclissi hanno incuriosito e addirittura spaventato molte popolazioni nel corso dei secoli. Riportiamo a seguire alcune curiosità:

immagine3b·       29 Maggio 1919 – Prima conferma della Relatività GeneraleIl 29 Maggio 1919 nella città di Sobral (Brasile) e São Tomé e Príncipe (Africa centro-occidentale) fu osservata un’eclissi solare totale. Grazie a questa eclissi, lo scienziato A.Eddington riuscì a misurare la curvatura della luce di una stella visibile in prossimità del Sole,  e quindi venne sperimentalmente confermata la teoria della relatività generale. Secondo la Teoria infatti una stella visibile in prossimità del Sole avrebbe dovuto apparire più esterna rispetto ad esso, in quanto l’attrazione gravitazionale del Sole avrebbe dovuto deviare la traiettoria della luce.

·        Nell’antica Cina

In cinese antico, il termine per Eclissi è ‘chih’, che significa ‘mangiare’. Così, i cinesi credevano che un drago stesse mangiando la Luna, pertanto sparavano con i cannoni contro la Luna stessa, nella speranza di spaventare il drago costringendolo a fuggire.
In effetti, la marina militare cinese ha sparato contro la Luna fino a non più tardi del XIX secolo, proprio a dimostrazione di quanto la tradizione culturale sulla Luna fosse radicata nella realtà locale.

·        29 Febbraio 1504 – Colombo e l’eclisse di Luna

Durante il suo quarto viaggio alla volta dell’America, nel 1503 Cristoforo Colombo si arenò sulle coste della Giamaica, nella baia di Santa Gloria, poiché le sue navi erano danneggiate. Anche le sue provviste erano ormai molto esigue, ma le popolazioni locali si rifiutarono di fornirgli del cibo, in cambio di gioielli. Allora Colombo escogitò un piano per ingannarli. Aveva a bordo una copia di uno dei libri di Regiomontano che conteneva le predizioni di eclissi Lunari – una delle quali prevista per il 29 febbraio 1504. La sera in cui si sarebbe verificata l’eclisse organizzò un incontro con i capi delle popolazioni indigene e disse loro che Dio era molto offeso e che avrebbe fatto sparire la Luna. Come previsto, un’ombra scura cominciò a passare sul disco Lunare. Gli indigeni spaventati dissero a Colombo che gli avrebbero fornito il cibo se avrebbe intercesso per loro presso Dio. Dopo essersi ritirato a “conferire” con Dio, poco prima della fine dell’eclisse totale Colombo tornò dicendo che Dio li aveva perdonati. La Luna tornò a splendere e Colombo ottenne le scorte di cibo.


Copyright © 2009 — Dip. di Fisica “E. Amaldi”, Univ. Roma Tre.

3 14 15 9 26 53: Oggi è il Pi Day

March 14, 2015 in mathematics, Uncategorized

Boston math lovers ready for rare Pi Day, Steve Annear su www.bostonglobe.com
Saturday will be a day for the math books, no matter which way you slice it.

For the first time in 100 years, Pi Day will fall on 3/14/15, matching up with the first five numbers that represent the ratio of a circle’s circumference to its diameter, 3.1415.

Going deeper, at 9:26:53 a.m. — and again at night — the day will represent the first 10 digits of the mathematical constant, bringing much merriment to members of the math community.

“It’s the Pi Day of the century,” said Michael Breen, public awareness officer at the American Mathematical Society, in Providence. “There’s a lot going on to celebrate.”

Tom Gaudette, principal academic evangelist at MathWorks in Natick, said pi reigns supreme among the mathematical constants.

The moment marks a once-per-century occurrence, as the date and time line up to spell out the first 10 digits of pi.

“That’s because everybody has to learn about pi,” he said. “You don’t have to learn about the other constants. Everyone learns to calculate the circumference of a circle before graduating high school.”

That, and it’s a good excuse to eat baked goods, which also happen to be circular. “It’s humorous, it’s a lot of fun, and people obviously enjoy eating pie,” he said. “For me, next year won’t be as important.”

The serendipitous date has led to officials at the Massachusetts Institute of Technology timing the release of student acceptance notifications to go live on the school’s admissions website right when the clock strikes 9:26 Saturday morning.

“Pi is a great number, for many reasons. It is a mathematical constant that occurs in many different scientific applications, and it is a homophone for something that is delicious,” said Stu Schmill, dean of admissions at the school. “Pi day falls at a nice time of year, as spring approaches and we are ready to celebrate.”

At Harvard University, students from the Harvard Undergraduate Mathematics Association, or HUMA, did some celebrating of their own to ring in “the most endlessly awesome number in the world.”

On Friday, a day prior to the unofficial holiday, members planned to gather for a pie-eating contest, and also compete to see who can recite the most numbers of pi from memory.

“I’m definitely really excited! This might be the only ‘real’ Pi Day that I and other current Harvard undergrads will see in our lifetime,” said Cherie Hu, vice president of HUMA.

The group has been holding Pi Day events for the past two years, attracting the attention of undergraduates, graduate students, and professors for a single cause — something that is as rare as the date itself.

“The day has been a great way to bring together the . . . Harvard undergraduate community at large,” she said.

Mark Lemay, 26, who runs the Math for People group in Cambridge, has also made plans.

“A few of us will meet up and talk about pi, and probably bring some appropriate snacks,” he said. “It’s always nice to have an excuse to eat food and talk about math.”

Others see it as a good way to promote the importance of math and geometry with a bit of fun baked in.

Michael Weiss, a retired math teacher who used to work at Bishop Fenwick High School in Peabody, said he and his wife are baking a pie and will top it off with crust shaped like the Greek letter used to signify pi.

“This pi day is . . . kind of an opportunity to have some fun with math,” he said. “It’s pretty neat because it isn’t going to happen again for another 100 years.”

Steve Annear can be reached at steve.annear@globe.com. Follow him on Twitter @steveannear.


Gerard Mercator

March 5, 2015 in mathematics, Uncategorized

Il 5 marzo 1512 nasceva nelle Fiandre Gerardus Mercator. Google gli dedica il doodle di oggi.
Sul lavoro e sulla figura di Mercatore è stato pubblicato nel 2004 da Mark Monmonier il volume
Rhumb Lines and Map Wars: A Social History of the Mercator Projection dal quale pubblichiamo un estratto.

Gerard Mercator was more than just a mapmaker. Although biographical dictionaries accustomed to single occupations typically treat him as merely a cartographer or a geographer, Mercator distinguished himself at various times as a calligrapher, an engraver, a maker of scientific instruments, and a publisher. No less impressive are his deep interests in mathematics, astronomy, cosmography, terrestrial magnetism, history, philosophy, and theology. Although biographers lament the lack of diaries, account books, and carefully archived personal correspondence, the historical record reveals Mercator as an introspective and energetic chap who was competent in science, honest and well liked, technically savvy and clever with his hands, curious about the world around him, successful as an entrepreneur, and well positioned to make a pair of substantial contributions to mapmaking.Mercator’s first biographer was Walter Ghim, his neighbor in Duisburg, the small German city where he lived from 1552 until his death in 1594. A twelve-term mayor of the town, Ghim contributed a short biography to the 1595 edition of Mercator’s Atlas, published posthumously by his youngest son, Rumold. Ghim’s essay is more a long obituary than a critical biography. The mayor praises Mercator as a “remarkable and distinguished man,” notes his “mild character and honest way of life,” and provides dates and other details for key events in the cartographer’s career. Thus we learn that Gerard Mercator was born at approximately 6 a.m. on March 5, 1512, in Rupelmonde, Flanders, where his parents Hubert and Emerentiana were visiting Hubert’s brother, Gisbert Mercator, “the energetic priest of that city.” (Flanders is roughly coincident with the northern part of present-day Belgium, and as figure 3.1 shows, the village of Rupelmonde is about ten miles southwest of Antwerp.) He died “82 years, 37 weeks, and 6 hours” later—a remarkably long life for the sixteenth century—after coping in his final years with partial paralysis and a cerebral hemorrhage. Ghim offers a detailed description of Mercator’s failing health and last rites but says little about the mapmaker’s early life.

figure 3.1
Places Mercator lived or visited (larger lettering), with present-day international boundaries and additional cities (smaller labels) as a frame of reference.

Scholarly interpretations of sixteenth-century Flanders helped historian of calligraphy Arthur Osley paint a richer picture. Although Mercator’s parents had little money—his father was a shoemaker and small farmer—Gisbert was at least better connected. Through his uncle’s influence, Gerard was enrolled at age fifteen in the distinguished monastic school at ’s-Hertogenbosch run by the Brethren of the Common Life, who accepted poor but bright boys willing to train for the priesthood. The brothers specialized in copying sacred texts, and their school excelled at teaching penmanship. In addition to learning Christian theology and Latin, Mercator developed a practical and lasting interest in the elegant italic script in which he engraved place names and interpretative text for his maps. He considered italic lettering more appropriate for scholarly writing than Gothic and other less formal (and often less legible) styles of handwriting, and in 1540 he published Literarum latinarum, quas Italicas cursoriasque vocant, scribendarum ratio (How to Write the Latin Letters Which They Call Italic or Cursive), a short manual that was influential in the adoption of italic lettering in cartography.


Various renderings of Mercator’s name invite confusion. Although his German father apparently went by Hubert Cremer, vernacular versions of the family name include de Cremer, Kramer, and Kremer. Krämer (the modern spelling) is the German word for merchant or shopkeeper, Cremer is its Dutch equivalent, and Mercator is the Latin version, which the future mapmaker adopted at ’s-Hertogenbosch. (Latin was the language of Europe’s educated elite, and young scholars routinely latinized their names.) Although Gerhard Cremer and Gerardus (or Gerhardus) Mercator might be more historically correct, American and British cartographic historians prefer the partly anglicized Gerard Mercator. A reasonable compromise, I’m sure, as an obsessive purist would need to write awkwardly about Gerardus Mercator Rupelmundanus (Gerard Mercator of Rupelmonde), the name under which Mercator enrolled at the University of Louvain in 1530 and published his epic world atlas.

At Louvain Mercator studied humanities and philosophy, attended lectures by the brilliant mathematician and astronomer Gemma Frisius (1508-55), and received a master’s degree in 1532. With his religious faith challenged by contradictions between biblical accounts of creation and Aristotle’s writings, Mercator occasionally felt stifled at Louvain, where doubt was akin to heresy. He began corresponding with a group of Franciscan preachers living in Antwerp and Mechelen (see fig. 3.1), and visited them several times to discuss theology and science. His confidants included Franciscus Monachus (ca. 1490-1565), a prominent geographer who produced a terrestrial globe around 1520 and is a plausible source of Mercator’s knowledge of northern lands. Although his absences from Louvain aroused suspicion, Mercator eventually resolved his concerns over the conflicting interpretations and, according to Osley, “emerged with strong Christian convictions, which remained with him.”

Reluctant to leave Louvain, Mercator pursued an academic apprenticeship centuries before the modern university gave us postgraduate education. In addition to convincing Frisius to instruct him in astronomy and geography, Mercator and his tutor persuaded Gaspar van der Heyden, a local goldsmith and engraver, to let Mercator use his workshop for making globes and scientific instruments. The three apparently collaborated on numerous projects, including maps and surgical instruments—Frisius was also a physician—and the future mapmaker either contributed to or witnessed all phases, from design to marketing. As Osley observes, by age twenty-four Mercator had become “a superb engraver, an outstanding calligrapher, and one of the leading scientific instrument makers of his time.” And as his later works attest, skill in engraving gradations and labels on brass and copper instruments proved useful in making printing plates for maps and globe gores.

An energetic learner, Mercator progressed quickly from globes to flat maps and from engraving to full authorship. In 1536 he engraved the italic lettering for Frisius’s terrestrial globe, which was assembled by pasting twelve printed gores onto a spherical papier-m‚ché shell nearly 15 inches (37 cm) in diameter. His role expanded from engraver to coauthor with the publication a year later of Frisius’s celestial globe, similar in size and manufacture. In 1537 he also authored and published his own map, a 17 by 39 inch (43 by 98 cm) cartographic portrait of Palestine engraved on copper and printed as six sheets, which formed a wall-size map when glued together. Mercator’s enduring interest in religion was no doubt a key motivation. Although he cites Jacob Zeigler as his principal source, the small map included with Zeigler’s book on the Holy Land, published five years earlier, is comparatively sketchy. Cartographic historian Robert Karrow, who labeled the map a “commercial success,” notes that it remained in print for at least four decades and provided the geographic details for Palestine for Mercator’s epic world map of 1569.

figure 3.2
A modern rendering by John Snyder of the double-cordiform projection used for Mercator’s 1538 world map. Reduced slightly from Snyder, Flattening the Earth, 37, fig. 1.27.

In 1538 Mercator published a 14 by 21 inch (36 by 55 cm) world map, laid down on the double cordiform (double heart-shaped) projection (fig. 3.2) pioneered in 1531 by the French mathematician Oronce Fine (1494-1555). Although Mercator borrowed the geographic framework from Fine, his map is more similar in content to Frisius’s terrestrial globe. As close examination of its features and place names reveals, he consulted additional sources but was the first to identify North and South America as separate continents. Also noteworthy are the suggestion of a Northwest Passage and the separation of Asia and North America, typically attached on early-sixteenth-century world maps. Aware of the uncertainty of some delineations, he scrupulously differentiated known, previously mapped coastlines from their more speculative counterparts in areas largely unexplored.


Mercator’s next publication was a detailed 34 by 46 inch (87 by 117 cm) map of Flanders, printed as four sheets in 1540. Prepared at the urging of Flemish merchants, the map was based on precise trigonometric and field surveys. Although some historians attribute the measurements to Mercator, who no doubt engraved the copper plates, others question whether the impoverished artisan had the time and resources for extensive fieldwork during the harsh winters of 1537-38 and 1539-40. A key skeptic is Rolf Kirmse, who observed that the distances portrayed are off by only 3.4 percent on average and that the average error of the angles is a mere 2° 20′. According to Kirmse, the timing of the surveys and their high level of accuracy point to Jacob van Deventer (ca. 1500-1575), a Dutch mapmaker who lived in Mechelen in the late 1530s and later produced a unique collection of town plans of the Netherlands for the king of Spain. Whoever the surveyor, there is no dispute about the map’s success and influence. Among the fifteen subsequent editions published between 1555 and 1594 is a smaller adaptation included in the 1570 world atlas by Abraham Ortelius (1527-98), a genial contemporary of Mercator.

In August 1536 Mercator married Barbara Schellekens, and the following year Barbara gave birth to their first son, Arnold. The couple eventually had six children, three boys and three girls. All three sons became mapmakers for a time at least, and Rumold (ca. 1541-1600), their youngest, became his father’s representative in England and supervised publication of the first complete edition of the Mercator world atlas.

Although prosperous and comparatively erudite, sixteenth-century Flanders was frequently engulfed in conflict between Protestant reformers and Catholic traditionalists, who in 1544 began a brutal effort to suppress Protestantism. Mercator’s letters to the friars in Mechelen as well as his more recent travels attracted the attention of religious extremists, who imprisoned him at Rupelmonde in March 1544. The zealots also held forty-two other suspects, including Joannes Drosius, to whom Mercator had dedicated his 1538 world map. Although protests by the mapmaker’s friends, colleagues, town officials, and a local priest won his release seven months later for lack of evidence, four of his fellow detainees were beheaded, burned at the stake, or buried alive.

Mercator’s religion remains ambiguous. Some writers consider him a Protestant (possibly a Lutheran convert), while others insist he remained a committed Catholic. Ghim and Osley ignore the mapmaker’s church affiliation altogether, Karrow confesses uncertainty, and the late Richard Westfall, who compiled the entry on Mercator for the Catalog of the Scientific Community Web site, emphatically states, “I find it impossible to tell.” Mercator was released from his imprisonment into Catholic territory, Westfall notes, but eight years later he left Louvain for Duisburg, in Cleve (a German duchy about fifty miles east of Flanders), which was Protestant. Even so, Catholic patrons continued to sponsor his projects and buy his maps.

Although religious unrest or outright persecution might have precipitated the move, the immediate incentive was a job offer from William, Duke of Cleve, who planned to open a university in Duisburg. Although the duke’s academy never developed, royal and commercial patrons continued to underwrite Mercator’s globes, maps, and scientific instruments. Especially significant is his 1554 map of Europe, which he started in Louvain. Engraved in copper and printed as fifteen separate sheets, the entire map measures 47 by 58 inches (120 by 147 cm) and, according to the ever enthusiastic Walter Ghim, a revised edition published in 1572 “attracted more praise from scholars everywhere than any similar geographical work which has ever been brought out.”

The 1554 edition’s portrayal of Britain underscores the difficulty of obtaining accurate geographic information about a country that feared invasion. According to Peter Barber, the British Library’s expert in medieval and early modern maps, Mercator relied heavily on existing maps, including a 1546 map of England published in Rome by George Lily, as well as reports from various unnamed correspondents, including the British astronomer-mathematician John Dee, who lived in Louvain from 1538 to 1540. Although his correspondents helped him add place names and refine coastlines, Mercator’s treatment does not mirror the markedly more accurate geometry of unpublished British surveys of the late 1540s and early 1550s. More surprising is the omission of several bishoprics that Henry VIII had established after he broke with Rome—surprising because Mercator, now living in Duisburg, had little to fear from church authorities. In Barber’s view, the omission reflects either ignorance of the bishoprics or a reluctance to antagonize a generous supporter, Cardinal Grenvelle, to whom Mercator dedicated the map.

More impressively accurate is Mercator’s 1564 map of England, Scotland, and Ireland, printed on eight sheets, which compose a 35 by 50 inch (88 by 127 cm) wall map. A curious inscription attributes its content to a prototype mysteriously acquired from an anonymous acquaintance. According to Ghim, “a distinguished friend sent Mercator from England a map of the British Isles, which he had compiled with immense industry and the utmost accuracy, with a request that he should engrave it.” Neither Mercator nor Ghim named the source, whose identity sparked the curiosity of map historians who, as Barber tells it, eagerly enlisted in a game of “find the friend.” After analyzing place names, shapes, and other details together and carefully assessing information available to plausible informants, Barber attributed the draft to John Elder, a Scottish Catholic who traveled freely between England and mainland Europe. Elder had access to the Royal Library, where he apparently compiled the map from ostensibly top-secret drawings by English surveyors. According to Barber’s hypothesis, Elder left England in late 1561, amid growing hostility between the Catholic and Protestant supporters of Mary Stuart and Elizabeth I, and gave the map to Cardinal de Lorraine, who persuaded Mercator to make the engraving.

Although powerful patrons like the Cardinal no doubt initiated specific projects, serendipitous influences were at least equally important. For example, Mercator’s famous 1569 world map, discussed in greater detail in the next chapter, was at least partly encouraged by his appointment to teach mathematics, as a part-time volunteer, in the gymnasium (high school) established by Duisburg’s city council in 1559. Mercator designed a three-year course that included geometry, surveying, and mathematical astronomy, and he taught the entire sequence once before surrendering the position to his second son, Bartholomew. A second example is his appointment around 1564 as cosmographer to the Duke of J’lich, Cleve, and Berg. According to Karrow, this nomination inspired Mercator to plan an enormous series of works on geography, cosmography, and history. The first part to be published was the Chronology (1569), an attempt to establish an accurate framework for world history. The Chronology included tables of solar and lunar eclipses and a conscientiously researched chronological list of political, cultural, scientific, and biblical events. Committed to completeness, Mercator earned a place on the Church’s list of banned books by including events associated with Martin Luther and a few other heretics.

figure 3.3
Based on a 1574 portrait, this elegant engraving of Gerard Mercator measuring a globe was first printed in the 1584 edition of Ptolemy’s Geography. It also appeared in the 1595 edition of Mercator’s Atlas. From Averdunk and M’ller-Reinhard, “Gerard Mercator,” frontispiece.

As a second installment of his vast, comprehensive work, Mercator published an authentic version of Ptolemy’s Geography,deliberately devoid of the distracting interpretations and misinterpretations by earlier editors intent on improving the Egyptian geographer’s seminal work. Mercator’s goal was an accurate portrait of Ptolemy’s second-century view of the world. To understand the present, the mapmaker believed, one must appreciate the past. The atlas, published in 1578, included Ptolemy’s twenty-seven maps, carefully restored, handsomely engraved, and supplemented by an index of place names and an enlarged boundary map of the Nile Delta. The maps vary slightly in size, with the typical display measuring approximately 13 by 18 inches (34 by 46 cm). Seven subsequent editions, published between 1584 and 1730, attest to the book’s importance to scholars. An engraved portrait of Mercator holding a globe and dividers (fig. 3.3) suggests that the mapmaker, now in his seventies, had become a brand name in geographic publishing.


While working on Ptolemy’s Geography, Mercator had started to compile maps for his celebrated world atlas, which would provide the modern geographical component of the massive treatise he envisioned. Resolving discrepancies between sources and engraving most of the plates himself was a slow process, especially for a seventy-year-old mapmaker. Trading off delay and fragmentation, he published Atlas sive Cosmographi† Meditationes de Fabrica Mundi et Fabricati Figura (Atlas, or Cosmographic Meditations on the Fabric of the World and the Figure of the Fabrick’d) in three installments: a 1585 edition, with 51 maps focused largely on France, Germany, and the Low Countries; a 1589 volume, with 23 maps taking in Italy and Greece; and the complete, 1595 edition, which reprinted the 74 maps issued earlier and added 28 new maps covering most of the remaining parts of Europe.

Because the atlas lacks detailed maps of Spain and Portugal, “complete” is misleading. Mercator no doubt desired a more comprehensive treatment of Europe, but time was running out. Weakened by strokes in 1590 and 1593, he died on December 2, 1594, leaving completion to his son Rumold and grandsons Gerard, Johann, and Michael. In addition to supervising printing, Rumold authored a world map and a regional map of Europe, Gerard signed regional maps of Africa and Asia, and Michael contributed a map of America. The project also provided employment for local artisans, who hand-colored the maps. Like other mapmakers, Mercator relied on colorists, mostly women, to enhance his otherwise bland line engravings.

What took so long? The late Clara LeGear, an atlas authority at the U.S. Library of Congress, identified four impediments: Mercator’s need to support himself with other projects, the difficulty of obtaining reliable geographic details, the slow pace of meticulous map engraving, and a shortage of skilled copperplate engravers. Mercator not only compiled all the maps for the atlas but also engraved the printing plates, with only occasional help from his grandson Johann and Frans Hogenberg, a skilled artisan who engraved most of the seventy maps for Theatrum Orbis Terrarum (Theater of the Whole World), published in 1570 by Abraham Ortelius, a publisher and map seller living in Antwerp.

Although a competitor, Ortelius was also a close friend of Mercator. So close, according to Walter Ghim, that Mercator deliberately delayed his own atlas. As Ghim tells it, Mercator “had drawn up a considerable number of models with his pen” and could easily have had them engraved. Yet he held up publication until Ortelius “had sold a large quantity of Theatrum…and had subsequently increased his fortune with the profits from it.” A nice story, perhaps, but the tedium of map engraving as well as the fifteen years between Theatrum and the first installment of Mercator’s Atlas suggests Ghim was spinning a yarn.

In pioneering the notion of a consciously organized book of mainly maps with a standard format printed in uniform editions of several hundred copies, Ortelius has a stronger claim than Mercator to the title Father of the Modern World Atlas. According to map historian Jim Ackerman, the innovative ingredient was Theatrum’s structure, not its format. After all, bound collections of portolan charts copied by hand had been around for more than a century, and books of printed maps published by Martin Waldseem’ller (1470-1522) and others in the early sixteenth century clearly qualify as atlases. What is noteworthy is Ortelius’s demonstration of atlas making as a systematic process orchestrated by an editor who selects information, standardizes content, and maintains quality.

Ortelius and Mercator had decidedly different views of the editor’s role. Whereas Ortelius relied largely on readily available sources, which he selected for reengraving, Mercator energetically sought new source materials and authored original maps, which he personally designed and engraved. Unencumbered by this spirit of scholarship, Theatrum not only beat Atlas onto the market but was so much more successful at the outset that Akerman considers it “remarkable that Mercator’s name [for a book of maps] should have eventually triumphed.”

figure 3.4
The title page of Mercator’s 1595 Atlashonors the mythic Atlas.

Remarkable perhaps, but hardly inexplicable. The “Atlas” of Mercator’s title commemorates an ancient ruler of Mauritania. In classical mythology, the immortal Atlas was forced to atone for his role in an unsuccessful revolt by supporting the heavens on his shoulders. In Mercator’s interpretation, Atlas was really a mere mortal magnified to legendary proportions for his accomplishments in science and philosophy. Although Mercator’s mythology is questionable, Atlas as a geographer and cosmographer provided an appropriate visual metaphor for the title page (fig. 3.4) of a massive work based on the hard work and persistence of the first truly hands-on atlas editor.


figure 3.5
In the expanded edition of Mercator’s Atlas published in 1606 by Jodocus Hondius and his sons, this engraved portrait of Mercator and Hondius signified the merger of two important cartographic trademarks. From Averdunk and Müller-Reinhard, “Gerard Mercator,” pl. 18.

As a word for a book of maps, atlasmight have vanished shortly after Mercator’s grandsons brought out a second complete edition of the Atlas in 1602. Apparently disappointed by sales, they sold the plates to the family of Jodocus Hondius (1563-1612), who ran a successful engraving and publishing business in Amsterdam. Hondius and his sons had a two-fold strategy for challenging the less meaty but still popular Theatrum. In 1606 they published a new, more geographically complete edition with forty additional maps. Recognizing the value of a brand name, Hondius listed Mercator as the author and himself as the publisher. A contrived engraving of the two collaborators seated at a table with globes and dividers (fig. 3.5) reinforced the continuity. To lower the cost of engraving, printing, and hand coloring, the Atlas maps, which measured about 14 by 18 inches, were simplified and reengraved to roughly 7 by 9 inches and published as the Atlas minor, a less expensive version introduced in 1607 and modeled after pocket-sized editions of Ortelius’s Theatrum. Translation of Mercator’s Latin narrative into Dutch, French, German, and English created a still wider market for the thirty editions of the full-size Mercator-Hondius Atlas published between 1606 and 1641. The Atlas minor enjoyed an even longer run in the twenty-five editions Hondius and his successors published between 1607 and 1738. By 1700 numerous other publishers were issuing atlases, and the term was well established.


figure 3.6
An excerpt from Mercator’s map of Brabant, Jülich, and Cleve showing Duisburg (bottom center) and part of Cleve, as portrayed in the electronic edition of his 1595 Atlas published in color by Octavo, “Examine Disc,” 155.

Perhaps the most compelling evidence of the Atlas’s endurance is its recent republication in CD format. In 2000 Octavo Digital Editions, an Oakland, California, firm headed by software designer John Warnock, issued a two-disc facsimile edition easily navigated with Adobe Acrobat Reader, the widely used electronic page-viewing application that Warnock helped develop. The “Read Disc” links Mercator’s Latin text to an English translation and includes insightful commentary by map historian Robert Karrow. The “Examine Disc” consists of high-resolution scans of a copy in the Lessing J. Rosenwald Collection of the Library of Congress. Readers can turn the pages of the 1595 Atlas, peruse its maps, and zoom in for a detailed look at the mapmaker’s conception of late sixteenth-century Europe. Figure 3.6, a close-up centered on Duisburg, where the mapmaker lived, illustrates the content and graphic detail, but the Octavo images, in full color, convey a fuller sense of the hand coloring and textured paper. Warnock’s version also exemplifies the extension during the 1990s of the word atlas to include structured collections of viewable geographic data published on CDs or the Internet. Mercator’s simple five-letter word apparently expresses the concept more effectively than the tedious synonym geospatial database.



Copyright notice: Excerpt from pages 31-46 of Rhumb Lines and Map Wars: A Social History of the Mercator Projection by Mark Monmonier, published by the University of Chicago Press. ©2004 by the University of Chicago. All rights reserved. This text may be used and shared in accordance with the fair-use provisions of U.S. copyright law, and it may be archived and redistributed in electronic form, provided that this entire notice, including copyright information, is carried and provided that the University of Chicago Press is notified and no fee is charged for access. Archiving, redistribution, or republication of this text on other terms, in any medium, requires the consent of the University of Chicago Press.

Mark Monmonier
Rhumb Lines and Map Wars: A Social History of the Mercator Projection
©2004, 232 pages, 52 halftones, 26 line drawings
Cloth $25.00 ISBN: 0-226-53431-6