DRAPER 2
famous equatorial telescope, with its aper- ture of twenty-eight inches, which was to prove of such value in photographing the spectra of the stars. Its mounting and its silvered spectrum were made with his own hands, and in 1872, after a long series of tests, he satisfied himself and others that his instrument was a success. Pres. Barnard, of Columbia College, wrote of it as "probably the most difficult and costly experiment in celestial chem- istry ever made." With the aid of his new instrument Prof. Draper obtained a photograph of the fixed lines in the spectra of stars, and, with but a single exception, no one by repeating the ex- periment has since claimed a share in this honor. The discovery of the gelat- ino-bromide "dry process" in photog- raphy greatly lessened the difficulties in the way of this exceedingly delicate branch of celestial investigation and en- abled him to secure upwards of one hun- dred of the spectra of various stars. In 1872 Prof. Draper obtained a photo- graph of the diffraction spectrum which has never been excelled. It comprised the region from below G, wave-length 4,350, to O, wave-length 3,440, on one plate. Small portions of the diffraction spectrum have since been taken on a larger scale, though none of them were veritable for determining the relative wave-lengths of the fixed lines. Secchi, in his masterly work on the sun, used an illustration from this photograph of Prof. Draper's, and the British Associa- tion recognized its value by reproducing and indorsing it as the best that had ever been taken. The transit of Venus in 1874 afforded an exceptional opportu- nity for the display of perfected photog- raphy, and Prof. Draper, as its ablest exponent, was appointed superintendent of the photographic department by the commission which was sent out by this government to observe the phenomenon. His work was so successful and so grati- fying to scientific men that it won from Congress a special gold medal, struck off at the Philadelphia Mint, and bear- ing the legend "Decori Decus Addit
6 DRAPER
Avito" — "He adds luster to ancestral glory." This was the first instance in the history of the United States that any such recognition was given by Congress to a scientist.
Perhaps Prof. Draper's most remark- able achievement was his discovery of oxygen in the sun. This was in 1S77, after a long and costly investigation of the lines in the solar spectrum. It was a revelation to scientific men which created intense interest, provoked much discussion and some criticism. A trip to Europe by Prof. Draper was one of its results. He laid his facts before the British Association and the French societies. The latter acknowledged the correctness of his views and applauded his discovery. There was a disposition to dissent from them among the English scientists, although the preponderance of opinion was in his favor. Subsequent investigations have tended to prove the soundness of his judgment. For the purpose of determining whether from an observatory in a high and dry region many of the obstacles now encountered in the use of very large telescopes could not be removed or greatly lessened, Prof. Draper made a trip to the Rocky Mountains in 1877, and undertook a series of experiments on the lofty plateau between the Rocky Moun- tains and the Sierra Nevadas. The conditions of the atmosphere, however, were found to be little more favorable than those met at lower levels, and the only conclusion that was arrived at was that the summit of a lofty mountain near the seacoast was best adapted to the pur- poses of astronomers. A total eclipse of the sun, observed by the professor from the same elevated standpoint the following year, afforded another illustra- tion of the nicety with which his photo- graphic apparatus registered celestial phenomena. The last two years of his life were devoted mainly to taking photo- graphs of the nebula in Orion, a feat which only those who are intimately acquainted with the subject can proper- ly appreciate. Only after the most
