Eighteenth-century eclipse maps by Halley and Whiston

Earlier this month I published a post at the H Word on ‘Halley’s Eclipse’ of 1715. It has been associated with Edmond Halley because, using the best theory and data then available, he made impressively accurate predictions of its timing and path, publicised through a broadsheet map and the Royal Society. As I explain in the post, however, he was not the only one to do so: London was a competitive market for scientific publications and authority.

This post is an appendix, where I can show more of the eclipse maps published than I could on the Guardian’s website. I should add, too, that these were not the first predictions or maps of solar eclipses, and that there were earlier German, Dutch and French maps.

Here, however, is Halley’s first map, from Eclipse Maps, which was published in advance of the event, encouraging observation. It is titled “A Description of the Passage of the Shadow of the Moon over England, In the Total Eclipse of the Sun, on the 22d Day of April 1715 in the Morning”. I am not sure where the original is kept, but it may be the same as that reproduced in black and white in Jay Pasachoff’s article on Halley’s eclipse maps, which is from the Houghton Library. The full text, which is not high enough resolution to read here, has been transcribed by Pasachoff.

Halley's predictive map of the 1715 eclipse, from Eclipse-Maps.com.
Halley’s predictive map of the 1715 eclipse, from Eclipse-Maps.com.

Halley seems to have produced more than one edition of the map before 22 April 1715 (O.S. – the anniversary was celebrated on 3 May N.S.), and also one after the event, showing the path as corrected by observations. This copy of his “A Description of the Passage of the Shadow of the Moon over England as it was Observed in the late Total Eclipse of the Sun April 22d, 1715 Manè” is from the Institute of Astronomy, University of Cambridge, where you can see some superbly high-resolution images.

Halley's map of the 1715 eclipse, produced and corrected after the event. Institute of Astronomy, University of Cambridge
Halley’s map of the 1715 eclipse, produced and corrected after the event. Institute of Astronomy, University of Cambridge

Halley came back to his winning formula when another eclipse rolled along. His map, published in 1723 (annotated November 17123 here), showed both the recomputed path of the 1715 eclipse and the predicted path of 11 May 1724. This image is from the Houghton Library’s Tumblr, where it is available in higher resolution. The text declares that the first map “has had the desired effect” in encouraging observation and uses this one to demonstrate that his predictions had been pretty good in 1715 and were worth acting on again.

Halley's map showing the 1715 and 1724 solar eclipses. Houghton Library (EB7 H1552 715d2b).
Halley’s map showing the 1715 and 1724 solar eclipses. Houghton Library (EB7 H1552 715d2b).

However, as my post discussed, William Whiston was also in the business of predicting eclipses and selling scientific paraphernalia.  Like Halley, he was making predictions based on John Flamsteed’s observations at the Royal Observatory and corrected with Isaac Newton’s theory, and encouraging observations. Whiston made comparison of his observations with Halley’s and his  two eclipse-predicting broadsheets are again from the Cambridge Institute of Astronomy’s Library here and here.

The one I think is the earlier from Whiston was dated 2 April 1715 and titled “A Compleat Account of the great Eclipse of the Sun which will happen Apr. 22 in the Morning”. It is much more text-heavy and technical in content, and the map is a celestial one, showing the positions of the heavenly bodies rather than the path of the shadow on Earth.

Whiston's broadsheet predicting the timing and path of the 1715 comet. Institute of Astronomy, University of Cambridge (AMI/11/B).
Whiston’s broadsheet predicting the timing and path of the 1715 comet. Institute of Astronomy, University of Cambridge (AMI/11/B).

A second broadsheet by Whiston did show the Sun’s shadow on the Earth, but from a global point of view. The title too emphasised that this was not just an English matter: “A Calculation of the Great Eclipse of the Run, April 22d 1715 in ye Morning, from Mr Flamsteed’s Tables; as corrected according to Sr Isaac Newton’s Theory of ye Moon in ye Astronomical Lectures; with its Construction for London Rome and Stockholme”. It also advertised an instrument that could be bought from Whiston.

Whiston's second 1715 eclipse broadsheet. Institute of Astronomy, University of Cambridge (AMI/11/C).
Whiston’s second 1715 eclipse broadsheet. Institute of Astronomy, University of Cambridge (AMI/11/C).

John Westfall and William Sheehan’s new book on observing eclipses, transits and occultations, indicates the Whiston and Halley’s estimates varied by about 25 miles, which perhaps puts the more triumphant claims of accuracy in perspective. I think (correct me below if I am wrong) that Halley’s prediction was the more accurate, but there was an element of luck involved. Above all, his map, showing geographical detail of England beneath the path of totality, was much more persuasive and appealing – this is the main reason that the 1715 eclipse became ‘Halley’s’.

Whiston had learned the importance of the image by 1724. His “The Transit of the Total Shadow of the Moon” this time showed familiar coastal outlines, although again other parts of Europe were included: Paris would be a better observing site than London this time. This version is from the Science & Society Picture Library and belongs to the Royal Astronomical Society.

Whiston's map showing the predicted path of the 1724 eclipse. Science & Society Picture Library/Royal Astronomical Society.
Whiston’s map showing the predicted path of the 1724 eclipse. Science & Society Picture Library/Royal Astronomical Society.

And so the maps continued: there are many to explore in the wonderful albums at Eclipse Maps. It was a flourishing business come eclipses in the 1730s and beyond, especially that of 1764, as many publishers jumped on the opportunity that Halley and Whiston had spotted in 1715. So too, of course, had the person that links all the images shown here: the engraver and cartographer John Senex, who deserves a much fuller biography on Wikipedia than this!

 

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Picturing science: Mapping the moon

A reproduction of a lunar map by H. Percy Wilkins, a “proto-Patrick Moore”, is on display at the National Maritime Museum. It makes an interesting side-show to the new major exhibition, Visions of the Universe. [Cross-posted from The H Word blog.]

Map of the Moon by H. Percy Wilkins
Sheet from 1951 ed. of Wilkins’ Map of the Moon. Source: National Maritime Museum

Given my recurring Picturing Science posts in this blog, I can’t avoid mentioning the new exhibition that has opened at the National Maritime Museum, Visions of the Universe. (Full disclosure: I have not been involved with this exhibition at all.) It has been getting some really nice reviews and previews, and anyone with an interest in astronomy or photography should make the trip.

Visions of the Universe exhibition at the National Maritime Museum

In this post, though, I want to highlight something else that is currently on view, within the main (free) museum. While the exhibition showcases what the space age has brought us, with extraordinary Hubble-type images and – the real hit, I think – a 13-metre long Mars Window, this other display offers the clearest possible reminder of how recently it is that any of this became possible.

In the NMM’s Compass Lounge (at the rear left of the Museum’s new entrance foyer), the several sheets of a 1951 map of the moon have been photographed and reproduced to show the complete 300-inch chart. It shows an extraordinary level of hand-drawn detail, achieved by its maker, H. Percy Wilkins (1896-1960), with the aid of distinctly earth-bound telescopes.

This map, versions of which he had been working on since the 1920s, was the largest-scale and most detailed of its time, combining Wilkins’ personal observations with data from the drawings, photographs and measurements of other astronomers. As his Wikipedia entry says, it was “considered by some as the culmination of the art of selenography prior to the space age”. Wilkins himself described it as “the World’s greatest Moon Map”.

The map was also, perhaps, one of the last productions of its kind. Not only was it published just on the cusp of the space age, but it was also the project of an amateur, working from his home near Bexleyheath with a 12½-inch, and later a 15½-inch, reflector. Wilkins did the work in his spare time, being employed first as a mechanical engineer and then a civil servant at the Ministry of Supply.

Title page of Wilkins' Map of the Moon
The title page of Wilkins’ Map of the Moon. Source: National Maritime Museum

Wilkins nevertheless found time to make telescopes, publish several works on popular astronomy and act as director of the British Astronomical Association’s Lunar Section. As well as founding the Section’s periodical The Moon, he was also, late in life, the first president of the International Lunar Society.

Two of Wilkins’ books were co-authored with another selenographic authority, Patrick Moore, to whom the Visions of the Universe exhibition is dedicated. I found online a reminiscence of Wilkins by an acquaintance describing him as a “proto-Patrick Moore”, but he was perhaps also a direct inspiration. In an obituary of his colleague, Moore wrote of the “prodigious amount of work” that went into the mapping project but, also, that “his personal enthusiasm was inspiring”. Moore felt a “deep sense of personal loss”.

Wilkins did not quite become the media star that Moore did, but he made “numerous broadcasts and television appearances”. You can, for example, see him (his telescope, his map, and his daughter) here in a 1953 Pathé newsreel. Somewhat more infamously, he made the news in 1954 when he announced his observation of “the most extraordinary feature known on the moon today”.

This was a curved shadow, already spotted and described as bridge-like by an American astronomer, John J. O’Neill. It was reported as a 20-mile arch, which can be seen clearly in the photographs reproduced in one of the newspaper reports, viewable at the bottom of the page here. It was, however, no more than a trick of the light, rather like the Face on Mars.

The episode seems to have damaged his credibility considerable and may be one of the reasons that he is less than well-remembered today. Part of the problem was that Wilkins spoke to the press and on the radio before submitting his, rather more cautious, observations to peer scrutiny, His case was not aided by his initially appearing to hint that the structure could be evidence of life on the moon: phrases like “looks artificial” and “almost like an engineering job” led some to leap to such conclusions, even if they were simply descriptive.

The “bridge” was not included in Wilkins’ map, although it did incorporate some other erroneous details. Nevertheless, NASA purchased at least one, and possibly several, copies of the reduced reproduction of his lunar chart when preparing for the Apollo moon landings. His map was also used to help match up the first photographs of the far side of the moon, produced by a Lunar 3 in 1959, with features visible from Earth.

As well as the originals of three editions of the maps themselves, the Museum also received a number of notebooks, all kindly donated by Wilkins’ daughter. The notebooks include formulae, photographs, newspaper cuttings, original drawings and observational notes, from Wilkins’ Kentish observatory and visits to professional observatories in France and the US. They are testament to his years of dedicated work.

When you go (as you must) to see the images, the ingenuity and the leaps that have been made in professional and amateur astronomical imaging on display in the major exhibition, do also remember to pop over to see “the World’s greatest Moon Map”.