Дава Собел – The Glass Universe: The Hidden History of the Women Who Took the Measure of the Stars (страница 5)

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MRS. DRAPER’S GLASS PLATES demanded examination by daylight. Although Pickering had heard much about these images, and even discussed them with the doctor the night of the Academy dinner in November, he had not seen them till now. He was accustomed to looking at spectra—the separated rays of starlight—through the telescope, using attachments called spectroscopes that former director Joseph Winlock had purchased in the 1860s, when spectroscopy came into vogue. The live view through the spectroscope turned a star into a pale strip of colored light ranging from reddish at one end through orange, yellow, green, and blue to violet at the other. The spectroscope also made visible many black vertical lines interspersed at intervals along the colored strip. Astronomers believed that the breadth, intensity, and spacing of these spectral lines encoded vital information. Though the code remained unbroken, a few investigators had proposed schemes to classify the stars by type, according to the similarities in their spectral line patterns.

On the Draper plates, each spectrum looked like a gray smudge barely half an inch long, yet some contained as many as twenty-five lines. As Pickering viewed them under a microscope, their detail stupefied him. What skill their capture demonstrated, and what luck! He knew of only one other person in the world—Professor William Huggins of England—who had ever succeeded in capturing a stellar spectrum on a photographic plate. Huggins was also the only man of Pickering’s acquaintance, aside from Dr. Draper, to have discovered an able astronomical assistant in his own wife, Margaret Lindsay Huggins.

Mrs. Draper agreed to leave her plates in Pickering’s care for a complete analysis, and returned to New York. She promised Mrs. Pickering, who was considered one of Cambridge’s most accomplished gardeners, to visit again in spring or summer, in the hope of seeing the observatory grounds in full bloom.

Pickering measured each spectrum with a screw-thread micrometer. By February 18, 1883, he could report to Mrs. Draper that he was finding “much more in the photographs than appears at first sight.” The computers had plenty to do in graphing the readings from his every half-turn of the screw, then applying a formula and computations to translate them into wavelengths. It became clear that Dr. Draper had demonstrated the feasibility of studying the stellar spectra by means of photography, instead of by peering through instruments and drawing a record of what the eye saw.

Pickering again pressed Mrs. Draper to publish an illustrated account, not merely to establish priority for her husband, but, more important, to show other astronomers the great promise of his technique.

For help with the preparation of the paper, Mrs. Draper asked a noted authority on the solar spectrum, Charles A. Young of Princeton, to contribute an introduction outlining Henry’s methods. Meanwhile she catalogued all seventy-eight plates in the spectra series, relying on Henry’s notebooks to specify the date and time of each photograph taken, the star name, the length of every exposure, the telescope used, and the width of the spectroscope slit, plus incidental remarks about observing conditions, such as “There was blue fog in the sky” or “The night was so windy that the dome was blown around.”

Pickering summarized the twenty-one plates he had scrutinized in ten tables with explanations. He reported the distances between spectral lines, stating the methodology and mathematical formulas employed to translate line positions into wavelengths of light. He also commented on the similar work being done by William Huggins in London, and ventured to categorize some of Draper’s spectra by Huggins’s criteria. When he sent his draft to Mrs. Draper for approval, she balked at the mention of Huggins.

“Dr. Draper did not agree with Dr. Huggins,” she wrote Pickering on April 3, 1883, concerning two of the stars in the series. Their nearly identical spectra both showed wide bands, which had made Huggins classify the two stars as a single type, but the Draper photographs revealed that one of these stars also had many fine lines between the bands, which set it apart from the other. “In view of this I should not like to accept Mr. Huggins’ classification as the standard when Dr. Draper did not agree with it.” Although Pickering had seen the abundance of fine lines she described, he found them too delicate for satisfactory measurement.

“You will not I hope be annoyed at my criticism,” Mrs. Draper added, “but I feel in publishing any of Dr. Draper’s work that I want his opinions represented as nearly as possible, now that he is not here to explain them himself.”

The Drapers had met William and Margaret Huggins while visiting London in June 1879, at the Hugginses’ home observatory on Tulse Hill. Mrs. Draper recalled Mrs. Huggins as a petite woman with short, unruly hair that stuck straight out from her head as though galvanized. She was half the age of her husband, but a full participant in his studies, both at the telescope and in the laboratory.

The two couples seemed destined to become either rivals or intimates. William gave Henry the benefit of his lengthier experience by offering helpful advice about spectroscope design. He also recommended a new type of dry, pretreated photographic plate that had lately come on the market. There was no need to paint liquid emulsion on these plates just prior to exposing them, and consequently they allowed for much longer exposure times. Before leaving England, the Drapers purchased a supply of Wratten & Wainwright’s London Ordinary Gelatin Dry Plates, which proved a boon indeed. They were particularly sensitive to the ultraviolet wavelengths of light, beyond the range of human vision. Unlike the old wet plates, the dry ones created a permanent record suitable for precision measurement. The dry plates gave the Drapers the wherewithal to photograph the spectra of the stars.

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THE PAPER ANNOUNCING the stellar spectra findings, “by the late Henry Draper, M.D., LL.D.,” appeared in the Proceedings of the American Academy of Arts and Sciences in February 1884. Pickering mailed copies to prominent astronomers everywhere. By return mail dated March 12, he received William Huggins’s indignant reaction. Huggins found some of Pickering’s measurements “very wild,” the letter said with emphasis. “I should be glad if you could see your way to look into this, because it would be better that you should discover the error & publish the correction, than that the matter should be pointed out by others. … My wife unites in kind regards to you and Mrs. Pickering.”

Pickering was certain he had not erred. And, as Huggins had never explicated his measurement procedures, Pickering stood firmly by his own. As they traded charges, Pickering forwarded Huggins’s letters to Mrs. Draper.

Now it was her turn to grow indignant. “I felt very sorry,” she wrote Pickering on April 30, 1884, “that you should have been subjected to such an ungentlemanly attack, through your interest in Dr. Draper’s work.” Before returning the letters to Pickering, she took the liberty of copying one, since “it is worth preserving as a curiosity of epistolatory literature.”

During this same time, Pickering was seeking assistants who might help Mrs. Draper advance her husband’s work to the next stage. He considered former director Joseph Winlock’s son, William Crawford Winlock, currently employed at the U.S. Naval Observatory, to be a very likely prospect, but Mrs. Draper rejected him. To her regret, she could not induce her preferred candidate, Thomas Mendenhall, to leave his professorship at Ohio State University. She channeled some of her frustration into the creation of the Henry Draper gold medal, to be awarded periodically by the National Academy of Sciences for outstanding achievements in astronomical physics. She gave the Academy $6,000 to endow the prize fund, and spent another $1,000 commissioning an artist in Paris to fashion a medal die featuring Henry’s likeness.

The spring of 1884 brought Pickering new money worries. The successful five-year subscriptions from generous astronomy enthusiasts had run their course, ending the accustomed annual stipend of $5,000. The director was covering various operating expenses out of his own salary, and even so was forced to let go five assistants. In a touching show of solidarity, observatory colleagues took up a collection to retain one of those who had been dismissed, and furnished “part of the required sum,” Pickering told his circle of advisers, “from their own scanty means.” He appreciated the “extraordinary efforts on the part of the observers, who have performed without assistance the work in which they were previously aided by recorders. This has required an increase in the time spent in observation, and has rendered the work much more laborious. While this evidence of enthusiasm and devotion to science is most gratifying, it is obvious that it cannot long be continued without injury to health. Indeed, the effects of over-fatigue and exposure during the long, cold nights of last winter were manifest in more than one instance.”