Huggins served two years as president of the Royal Astronomical Society, 1876-1878. The work that he would be best known for was behind him: his collaboration with Miller—who had died suddenly in 1870 — exploring stellar spectra, his discovery of the emission spectra from planetary nebulae, and his bold application of theory to develop a method of measuring stellar motion in the line of sight. He had reached the pinnacle of his scientific career.

Thanks in part to Margaret's assistance, Huggins was able to continue his productive scientific research until he was in his late seventies. From the late 1870s until he returned the Royal Society's telescope in 1906, Huggins attacked several important problems. He continued his quest to photograph stellar and nebular spectra. He experimented with photographic techniques and published a major article on the photographic spectra of stars in the ultraviolet portion of the spectrum. He tried to make workable an idea he had to photograph the solar corona in the absence of an eclipse. Emerging victorious from a controversy with the solar physicist Lockyer, he proved correct his belief that the ''chief nebular line,'' though extremely close to lines of both nitrogen and magnesium, did not, as he had earlier thought, correspond to the line of any known element. Most importantly, in 1882, he and Margaret were the first to photograph a nebular spectrum, that of the great nebula in Orion. The spectrum of the nebulae are more difficult to photograph than those of stars, because their light is generally fainter.

However, even with Margaret's help, Huggins could not stay ahead of the competition in the areas of investigation that most interested him. One of his great rivals was the New Yorker

Henry Draper, a wealthy and talented amateur whose influence on the study of the ''construction of the heavens'' reached far into the twentieth century.

Draper, 13 years younger than Huggins, had also been fascinated with daguerrotypes as a youth. He studied medicine at the University of the City of New York (now New York University) and incorporated daguerrotypes of microscopical images of blood cells in his thesis.

At 20, having completed his medical studies before the age at which he would be allowed to graduate, he made a trip to Europe with his older brother. In Ireland he visited William Parsons and his ''Leviathan'' reflecting telescope. During this visit he became interested in combining photography and astronomy. He explained in an article: ''On returning home in 1858, I determined to construct a similar, though smaller instrument; which, however, should be larger than any in America, and be especially adapted for photography.''39 In 1861, after receiving some advice from John Herschel on the construction of reflecting telescopes, he erected a private observatory on his father's estate at Hastings-on-Hudson, New York, and began taking daguerro-types of the Sun and Moon.

In the mid-to-late 1860s, when Huggins was publishing his work on stellar and nebular spectra and just beginning his work on the radial motion of stars, Draper was following a similar course, investigating the spectra of the elements and photographing stellar spectra. Draper married the former Anna Palmer during this period and, like Huggins in the late 1870s, found his wife to be an enthusiastic partner in the laboratory and at the telescope.

In August 1872 Draper succeeded, as mentioned earlier, in photographing the spectrum of a star, Vega, beating Huggins in this respect by four years.

In the spring of 1879, when Huggins was 55 and Draper 42, the rivals met face-to-face on the occasion of Draper's visit to the Tulse Hill Observatory. Draper learned of improvements in photographic emulsions from the Hugginses and returned to his own observatory with a renewed feeling of encouragement.

This was a period of great advances in stellar spectrum photography. Draper wrote in a scientific article, ''It is only a short time since it was considered a feat to get the image of a ninth magnitude star, and now the light of the star of one magnitude less may be photographed even when dispersed into a spectrum.''40 Draper hoped to take long-exposure shots of the Orion nebula, a perennially interesting object, but he died before he could complete his plans, in November 1882. He suffered from double pleurisy contracted as a result of exposure to severe cold on a hunting trip in the Rocky Mountains.

Draper's influence on the course of astro-photography, and his challenge to Huggins, surprisingly, did not end with his death. Edward Pickering, the director of the Harvard College Observatory, persuaded Anna Draper to transfer her husband's telescopes to Harvard and to fund research on stellar spectra that he had hoped to continue. The resulting Henry Draper Memorial fund, established in 1886, paid for a photographic survey of bright stars and the detailed study of stellar spectra—just the kind of study Huggins contemplated. To help devise a classification scheme and to carry out the analysis of the spectra, Pickering hired a Scottish immigrant and single mother, Williamina (''Mina'') Fleming. Pickering had first employed Fleming as his housekeeper, but gave her a more intellectually challenging job when he became aware that she had been a teacher and had a strong educational background. She was the first of a small army of women assistants at Harvard, many of them college-educated, who are still much spoken of today in the astronomical community.

Fleming and Pickering created a system ranking the stellar spectra with the letters A through M according to complexity (not to be confused with Fraunhofer's letter labels for individual lines in the solar spectrum). The simplest A-type spectra had a restricted set of lines later identified with helium, while other classes displayed hydrogen lines in varying degrees of intensity, and most red stars, classified as M, showed richer spectra with strong calcium lines.

In the late 1880s, Fleming was well on her way to classifying the more than 10 000 northern hemisphere stars that would be included in the first Draper catalog, which appeared in 1890. She was joined in 1886 by Annie Jump Cannon, who catalogued southern-hemisphere stars and made her own mark on the classification system. Other assistants in the ''corps of women computers'' made mathematical calculations—correcting star positions for the effects of precession, for example.

Pickering's ''harem,'' as historians have termed it, posed a real threat to other astronomers working in the new field of spectrum analysis, for by employing women at a fraction of the pay male assistants would have received, Pickering could efficiently analyze the reams of data that were quickly being generated through photography.41 An article in Popular Astronomy that appeared in 1898, shortly before Fleming published the first Draper catalog, publicized for a wide audience the opportunities Pickering had given to women.

''The application of photography to astronomy, whereby the determination of star-positions, spectra-type, variability, etc., [hasj become laboratory work rather than Observatory work, has wonderfully increased the opportunities for woman in pursuit of the truths of nature,'' the author wrote. ''But the most extended application of the aid of women in this specialty has been under the directorship of Professor Edward Pickering at Harvard Observatory, where a large force of women is constantly employed under the supervision of Mrs. Fleming.''42

Whether or not Huggins read this article, he certainly knew of Pickering's corps of assistants and felt the pressure from across the Atlantic. He had been interested in the classification of stellar spectra, but it hardly seemed possible to make his mark in the field against the competition from Harvard. In 1887, shortly after the Draper fund became a reality, he wrote to the astronomer George Stokes for advice, noting particularly the ''magnificent scale'' of operations that the Draper endowment would allow.

''The question is, is it worth my while to continue working in this direction now that it is being done under circumstances with which no zeal and perseverance on my part will enable me to be in an equal position,'' he wrote. ''It is scarcely worth while to do what will be done well, no doubt, elsewhere—I do not at this moment see clearly any entirely new direction of work.''43

In 1888, the Hugginses received another jolt, this time in the area of research on nebulae. Isaac Roberts, an English amateur astro-photographer, had succeeded in taking a photograph of the faint Andromeda nebula, showing its oval form in detail. Huggins had previously obtained a faint spectrum of the same object, which appeared continuous and therefore coarsely resembled the absorption-line spectrum of a star or collection of stars, rather than rather than the bright-line spectrum of a gaseous nebula. Roberts's photograph, however, seemed to show a large nebulosity around a central bright core. Huggins quickly arrived at a view that synthesized elements of both the recent photographic view and the early attempt at a spectrum analysis: he saw in the Andromeda nebula a single star in the process of evolving from a nebula.

Huggins described the photograph in another letter to his friend Stokes. He wrote that the Andromeda nebula showed ''for the first time to the eye of man its true nature. A solar system in the course of evolution from a nebulous mass! It might be a diagram to illustrate the Nebular Hypothesis! I never expected to see such a thing. There are some 6 or 7 rings of nebulous matter already thrown off, & in some of them we see the beginning of planetary condensation & one exterior planet fully condensed. The central mass is still larger, to compare it with the solar system, say as large as the orbit of Mercury. The rings are all in one plane & the position is such that we see it obliquely.''44

In the observatory notebook Margaret noted the Huggins' somewhat competitive joint response to the photograph: ''It would be of special interest we think to supplement this remarkable photograph with some photographs of the spectrum of this neb. Mr. Roberts' work gives the body: if we can get good spectra we should have the soul.''45

Unfortunately for the Hugginses, and for all astronomers laboring to make sense of the nature of the nebulae, the light from the Andromeda nebula is so feeble that a photographic spectrum would not be obtained for years to come. In January 1899, the German astronomer Julius Scheiner, working at the Potsdam observatory, captured the exceedingly faint spectrum with a 7j hour exposure. As Huggins' earlier, non-photographic study had indicated, it proved to be a stellar spectrum, as would be expected for a distant cluster of stars. In the meantime, while waiting for the kind of strong evidence that the spectrum would provide, astronomers could only speculate, and the normally cautious Huggins clung to the Laplace ''nebular hypothesis'' as an explanation for the phenomenon he saw in Roberts's photograph.

Throughout this period of increasing competition with other astronomical spectroscopists and photographers, Huggins had never mentioned Margaret's assistance in his many scientific papers. But spurred, perhaps, by the threat of being trounced in one of his particular lines of investigation, he finally did so in 1899. Huggins was embroiled in a controversy over the distinction between the chief nebular line and a line arising from magnesium. To add weight to his argument, it was convenient for him to include Margaret's observations in his report, as those of an independent witness confirming his. Her name thus appeared with his as a co-author. He explained in the introduction to the paper, ''I have added the name of Mrs. Huggins to the title of the paper, because she has not only assisted generally in the work, but has repeated independently the delicate observations made by eye.''46 In effect, he was able to claim a more authoritative result with her help, without entering into a collaboration with a peer or hiring a research assistant—and without acknowledging the full extent of her assistance.

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