Henry Draper. 91 
on investigations at his house in New York, those being 
selected for the purpose which did not require a telescope. At 
first, two rooms in the third story were devoted to these 
researches, But in 1880 he built a special physica! laboratory 
as the third story of his stable in the rear of his house, this 
laboratory being connected with the house by a covered way. 
e equipment of this laboratory was superb. A siderostat by 
Alvan Clark & Sons, placed upon the roof, furnished abundant 
sunlight, directed to any part of the room by a secondary 
mirror, An Otto gas-engine of four-horse power gave motion 
to three dynamo-machines for the production of electric cur- 
rents. One of these was a Gramme machine, wound double, 
and which by an ingenious modification of his own, could be 
made to give a continuous or alternating current at will. The 
second was an Edison machine, used mainly to light the labora- 
tory by means of incandescent lamps. The third was a Maxim 
machine used for producing are lights and also to feed the field 
of the Gramme machine. For the production of the electric 
spark, an induction coil of the largest size was employed, 
made by Ruhmkorff. Used with the direct current it gave 
15-inch sparks readily, though the safety points were usually 
set at 10 or 12 inches to Gand perforation. With the Gramme 
direct current this coil yielded 1000 ten-inch sparks per minute. 
With the alternating current, the spark, though silent and 
only one-quarter as long, was of much greater volume; so that 
when heavily condensed, the discharge was like the rattle of 
musketry. The optical and photographic appliances were of 
the finest. Complete spectroscopes and cameras were there, us 
well as the lenses, prisms and gratings, of various materials and 
of the best workmanship, needed to extemporize those in 
research. A lathe, file bench and carpenter’s bench, each with 
its full set of tools, completed the appointments of this beauti- 
fully finished room. 
With these facilities at his command, the original work 
which Dr. Draper did was of an exceedingly high order. Upon 
the completion of his large reflector, he applied it at once to 
the photographic reproduction of stellar spectra; and in 1872 
he obtained a photograph of the spectrum of a Lyre (Vega) 
showing dark lines; a result then unique in science. Continu- 
ing his labors he obtained more than a hundred stellar spectra 
of great excellence; latterly, and especially when he use 
photographically-corrected refractor, taking upon the same plate 
the spectrum of Venus, Jupiter or the moon, for reference. In 
1878, he published the finest photograph of the diffraction spec- 
trum ever made. It included upon a single plate the region 
from wave-length 4350, below G, to wave-length 3440, near 
A steel plate from this photograph was introduced by 
