FUNDAMENTAL CONCEPTIONS 373 



stance and in obedience to gravitation, is now generally understood. 

 Later on, discoveries concerning the revolutions of the components 

 of binary stars in elliptical orbits extended the hypothesis of like- 

 ness throughout the stellar universe. The discovery that the sun, 

 like all the stars, is moving through space approximately in a straight 

 line, at a velocity comparable with the velocities of motion among 

 the stars, irresistibly led to the conclusion that, from the viewpoint 

 of any star, the sun would be seen as a small star differing in no dis- 

 coverable respect from others of the same brightness. These were a 

 few of the points suggesting essential unity of law and matter through- 

 out the universe. Such ideas are removed by a great gulf from those 

 which prevailed at the beginning of the Christian Era. 



The introduction of researches in astrophysics raised this line of 

 induction to a new plane of logical perfection. It proved that the 

 physical condition of the stars, broadly considered, resembles that of 

 the sun. It showed that the radiance of self-luminous bodies is attrib- 

 utable to the same cause which is needed for a similar effect at the 

 surface of the earth. Moreover, it showed that there is remarkable 

 likeness in the chemical constitution of various bodies throughout 

 the visible universe, specifically, that hydrogen, iron, and other 

 elements are quite universally constituents of the most widely 

 separated of the celestial bodies. The chemical elements existing in 

 the sun were found to be very nearly identical with those found on 

 the earth; and what is more remarkable, the progress of chemical 

 investigation of terrestrial elements served to increase the evidence 

 of apparent likeness in chemical constitution between the sun and the 

 earth. 



Thus, from a speculation, carefully guarded with limitations in its 

 expression, the idea of essential likeness of natural phenomena in their 

 operations throughout the universe was developed into a theorem 

 which it would now seem childish to doubt. This conclusion is the 

 joint product of the two branches of astronomical science. In this 

 special line astrophysics, the newer branch, has borne a very import- 

 ant part; and it would seem that, in a future of great promise, its 

 share must be still more conspicuous. 



Summing up, now, the results of human experience in the history 

 of astronomical investigation, we trace the influence of two intellect- 

 ual conceptions which appear to have inspired all that has been 

 done. The first is, that all the observed phenomena of motion can 

 be referred to fundamentally simple geometrical ideals as to their 

 real origin. The second is that the essential qualities of matter and 

 the operations of nature throughout the universe are everywhere 

 virtually the same. 



