420 Hi. Draper— Photographing the 
and interpret these results, and this is the direction I have 
sought to pursue. 
There is but one mode of investigation that can add materi- 
ally to the knowledge Astronomy has given us of the.heavenly 
bodies; that is the spectroscopic. This in its turn is capable 
of a subdivision into two methods, one by the eye, the other 
by photography. Each of these has its special advantages and 
each its defects. The eye sees most easily the middle regions 
of the spectrum, and can appreciate exceedingly faint spectra ; 
by the aid of micrometers it can map with precision the posi- 
tion of the Fraunhofer lines, and by estimation it can with tol- 
erable accuracy approximate to the relative strength, breadth 
and character of these lines. The character of the spectrum 
star at the focus of the telescope has changed place ty of a0 
inch the light no longer falls on the’ slit of v; spectroscope. 
The changes of the earth’s atmosphere in regard to photo 
condition of the air, which may increase the length of expo* 
ure required forty times or more. : 
It will, from what has been said above, be readily perceived 
that a research such as this consumes a great deal of time, 1? 
fact these experiments and the preparations for them have 
has also some 2s tk advanta 
ie ney eee lel 3 ies. 
et aac sa A |e 
already constructed a silvered glass reflector Z a | 
