CELESTIAL SPECTROSCOPY. 101 
the Milky Way in Argus, which to the eye is void of stars, is in reality 
uniformily covered with them. Also, quite recently, Mr. George Hale 
has photographed the prominences by means of a grating, making use 
of the lines H and K. 
Stellar distributions —The heavens are richly but very irregularly 
inwrought with stars, the brighter stars cluster into well-known groups 
upon a background formed of an enlacement of streams and convoluted 
windings and intertwined spirals of fainter stars, which becomes richer 
and more intricate in the irregular rifted zone of the Milky Way. 
We, who form part of the emblazonry, can only see the design dis- 
_torted and confused; here crowded, there scattered, at another place 
superposed. The groupings due to our position are mixed up with 
those which are real. 
Can we suppose that each luminous point has no relation to the others 
near it than the accidental neighborship of grains of sand upon the 
shore, or of particles of the wind-blown dust of the desert? Surely 
every star, from Sirius and Vega down to each grain of the light dust 
of the Milky Way, has its present place in the heavenly pattern from 
the slow evolving of its past. We see a system of systems, for the 
broad features of clusters and streams and spiral windings which mark 
the general design are re-produced in every part. The whole is in motion, 
each point shifting its position by miles every second, though from the 
august magnitude of their distances from us and from each other, it is 
only by the accumulated movements of years or of generations that 
some small changes of relative position reveal themselves. 
The deciphering of this wonderfully intricate constitution of the 
heavens will be undoubtedly one of the chief astronomical works of 
the coming century. The primary task of the sun’s motion in space, 
together with the motions of the brighter stars, has been already put 
well within our reach by the spectroscopic method of the measurement 
of star motions in the line of sight. 
From other directions information is accumulating; from photo- 
graphs of clusters and parts of the Milky Way, by Roberts, in this 
country, Barnard, at the Lick Observatory, and Russell, at Sydney; 
from the counting of stars, and the detection of their configurations 
by Holden and by Backhouse; from the mapping of the Milky Way by 
eye, at Parsonstown; from photographs of the spectra of stars, by Pick- 
ering at Harvard and in Peru, and from the exact portraiture of the 
heavens in the great international star chart which begins this year. 
I have but touched some only of the problems of the newer side of 
astronomy. There are many others which would claim our attention if 
time permitted. The researches of the Earl of Rosse on lunar radia- 
tion, and the work on the same subject and on the sun, by Langley. 
Observations of lunar heat with an instrument of his own invention 
