iS82] y)')l [Barker. 



inspired him with a desire to construct one like it, though on a smaller, 

 scale, and turned his attention toward astronomy and astronomical piioto- 

 graphy. Soon after his return he began the construction of a metal specu- 

 lum, fifteen inches in diameter, completing it in 1860. Subsequently he ac- 

 cepted a suggestion contained in a letter written to liis father by Sir John 

 Herschel, and abandoned speculum metal for silvered glass. In the year 

 1861, he made several mirrors of silvered glass, 15i inches in diameter. 

 The best of these was mounted as a Newtonian telescope, in a small wooden 

 observatory erected at Hastings-on-Hudson, his father's country seat. The 

 details of grinding, polishing, silvering, testing and mounting this reflec- 

 tor, all of which he did with his own hands, were published as a mono- 

 graph by the Smithsonian Institution. This publication has had a de- 

 served popularity, and has become the standard authority on the subject. 

 Much experimental work was done with this telescope ; that which is best 

 known, being his photograph of the moon. More than 1500 original 

 negatives were taken with this instrument. They were one and a quarter 

 inches in diameter, but such was the perfection of their detail thit they 

 bore enlargement to three feet, and in one case to fifty inches without in- 

 jury. The success of this mirror stimulated him to undertake a still 

 larger one, and, in 1870, he finished a silvered glass mirror, twenty-eight 

 inches in diameter. A new dome was built for it by the side of the old 

 one, the mounting being equatorial, and the telescope Cassegrainian ; 

 though subsequently a plane secondary mirror was substituted for the con- 

 vex one. A refracting telescope of five inches aperture was attached to the 

 tube of the reflector, as a finder. With this larger instrument, work was 

 at once begun upon photographic spectra ; and, in 1873, a beautiful photo- 

 graph was obtained of the spectrum of a Lyrie (Vega), which showed 

 the dark lines ; a step far in advance of anything which had been accom- 

 plished in this direction up to that time. Desiring to make simultaneous 

 eye-observations, Dr. Draper, in 1875, placed upon the same axis, a re- 

 fracting telescope of twelve inches aperture, made bj^ Alvan Clark & 

 Sons. In 1880, this was exchanged for another refractor by the same mak- 

 ers, of eleven and a half inches aperture, but furnished with an additional 

 lens to serve as a photographic corrector. The work of stellar spectrum 

 photography went steadily on, the new refractor now doing the principal 

 work. More than a hundred such photographs were made, most of these 

 having upon the same plate a photograph of the spectrum of Jupiter, 

 Venus, or the moon. These latter, giving the solar lines by reflection, 

 enabled the stellar lines to be identified by direct comparison. 



Reflecting on the extreme sensitiveness of the dry-plate process in pho- 

 tography, he was led to experiment on the reproduction of nebulae by its 

 means ; and on the 30th of September, 1880, he succeeded by an exposure 

 of fifty-seven minutes in obtaining a photograph of the nebula in Orion. Sat- 

 isfied now that the idea was an entirely feasible one, he devoted himself un- 

 interruptedly to securing the greatest possible perfection in the driving 

 clock and to improving the details of manipulation. In March, 1881, a 



