141 
THE USE OF THE SPECTKOSCOPE IN ASTKONOMICAL 
OBSEEVATION. 
By KICHAKD A. PEOCTOK, B.A., F.E.A.S. 
Authoe of Sattjen and its System,” Half-Hodes with the 
Telescope,” &c. &c. 
[PLATES XLII. AND XLIII.] 
T he manner in which the spectroscope has taken its place 
among astronomical instruments presents a remarkable 
contrast to that in which the telescope was received. In the 
case of the latter instrument all the advantages derivable from 
the new invention were at once recognised, yet the instrument 
made its way but slowly into use, and the various appliances by 
which At is rendered available as a means of advancing the 
science of astronomy were devised at periods separated by long 
intervals. But with the spectroscope the case is wholly dif- 
ferent. The power which the instrument gives the astronomer 
was at first far from being obvious. That it was a wonderful 
means of research was indeed clear ; but certainly he would 
have been a bold reasoner who would have ventured ten years 
ago to predict that the spectroscope would take up the 
position it now occupies as an aid to astronomical research. 
Already it has resolved problems which would have been deemed 
altogether insoluble ten years ago ; and it has answered ques- 
tions which, at first sight, would seem to lie out of its proper 
range of action — questions, for example, affecting the motion 
as well as those affecting the constitution of the celestial orbs. 
Undoubtedly the sudden growth of the new analysis is mainly 
due to the good fortune which has placed its application in the 
hands of a physicist possessing a combination of qualities 
rarely met with, but which were absolutely necessary in the case 
of the pioneer of the new line of scientific advance. Extra- 
ordinary skill in observation and manipulation, an intimate 
acquaintance with optical and chemical laws, extreme caution 
in the interpretation of observed phenomena, and unremitting 
perseverance and patience in conducting experiments tending 
