DRAPER 331 DRAPER ever, lay in an altogether different direction, so he abandoned the practice of medicine, except the chair of physiology in the academic department of the University, accepted in 1860, and six years later he was installed professor of physiology in the medical department, but his desire to devote his attention more closely to astronomical matters in which he had al- ready acquired well-deserved distinction prompted him to sever his connection alto- gether from his alma mater. The interest manifested by the elder Draper ill photography — he having been allowed by his friends the honor of having taken what in 1839 was known as the first Daguerreotype — was the stimulus for the utilization of the art in determining the character of celestial bodies. In his observatory, on his father's grounds, at Hastings-on-the-Hudson, he made his ob- servations and an incredible number of ex- periments in furthering his work. His first investigations in science were made when an undergraduate in the medical department at the age of twenty, by a series of experiments on the functions of the spleen, aided by micro- scopic photography, an art then in its infancy. It was in the course of this research that he discovered the great advantage possessed by protochloride of palladium in darkening collo- dion negatives. Shortly after his return from Europe he constructed a reflecting telescope of fifteen and one-half inches diaineter, with which he was enabled to procure a photograph of the moon fifty inches in diameter, the largest ever made. Prof. Draper was the first to demonstrate the superior value of chemically pure silver over all known substances in the construction of the spectrum. This was the result of the experiments resorted to in the construction of his 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 mountings and its silvered spec- trum 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 chemistry 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 experiment has since claimed a share in this honor. The discovery of the gelatino-bromide "dry process" in photography greatly lessened the difficulties in the way of this exceedingly delicate branch of celestial investigation and enabled him to secure upwards of one hundred of the spectra of various stars. In 1872 Prof. Draper obtained a photograph of the diffraction spectrum which has never been excelled. It comprised the region from below G, wave-length 4,3.^0, to O, wave-length 3,-140, on one plate. Small portions of the dif- fraction spectrum have since been taken on a larger scale, though none of them were verli- able for determining the relative wave-lengths of the fixed lines. Secchi, in his masterly work on the sun, used an illustration from this pliotograph of Prof. Draper's, and the Briti^^h Association recognized its value by reproduc- ing and indorsing it as the best that had ever been taken. The transit of Venus in 1874 afforded an exceptional opportunity for the display of perfected photography, 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 gratifying to scientific men that it won from Congress a special gold medal, struck off at the Phila- delphia Mint, and bearing the legend "Decori Dccus Addit Avito." ( He adds luster to ances- tral glory.) This was the first instance in the history of the United States that any such recognition was given by Congress to a sci- entist. Perhaps Prof. Draper's most remarkable achievement was his discovery of oxygen in
- he sun. This was in 1877, 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 lat- ter acknowledged the correctness of his views and applauded his discover}'. There was a dis- position to dissent from them among the English scientists, although the preponderance of opinion was in his favor. Subsequent in- vestigations have tended to prove the sound- ness 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 tele- scopes could not be removed or greatly les- sened. Prof. Draper made a trip to the Rocky Mountains in 1877, and undertook a series of experiments on the lofty plateau between the Rocky Mountains and the Sierra Nevadas. The conditions of the atmosphere, however,
