REPORT OF COMMITTEE ON OBSERVATORIES 23 



able cases. Nevertheless, we shall be able to verify our conjecture 

 in part, though we shall find that motion rather than brightness is 

 the better criterion as to the distances of stars. Later we shall dis- 

 cover that we can test the relative distance of one large aggregation 

 of stars from another, through one of the generalizations resulting 

 from an investigation of the solar motion. Now, we shall have 

 arrived at the point when we shall feel that we may some time see 

 the stars in space of three dimensions — when we shall not only be 

 able to make a flat picture of their relations as they appear to the 

 eye upon the celestial vault, but shall also be able to construct a 

 model showing the special and general relations in distance in space 

 of three dimensions. Astronomy is standing at this point now. It 

 takes some pride in what it has accomplished in this line already ; 

 but it is also more dissatisfied than ever with the amount of accu- 

 rate knowledge which it has, because it sees how comparatively 

 easy it would be to increase this knowledge in a very large ratio. 



Again, parallel with these researches upon the motions and dis- 

 tances of the stars, there has been growing in importance another 

 class of inquiries. Arming the telescope with a new appliance, the 

 spectroscope, the evidence of universal motion among the stars, 

 whether toward or away from the sun, has been most brilliantly 

 confirmed. In this way the solar motion has been verified, and the 

 approximate velocity of the sun in its flight through space has been 

 determined. 



Through its power of physical and chemical analysis the spectro- 

 scope has brought to light a collection of new facts of the highest 

 importance in their bearing upon cosmical problems. It has shown 

 the presence of terrestrial substances everywhere among the stars. 

 It has demonstrated anew and more convincingly that the sun is a 

 star, and even that there are multitudes of stars closely resembling 

 it in their physical condition. It has shown us something of what 

 is going on in the development of suns, or stars, revealing them at 

 all stages of evolution and connecting one with another by imper- 

 ceptible gradations from the newest to the oldest forms. 



The unity of the stellar universe is thus demonstrated from three 

 distinct points of view, and the conviction is brought home to us 

 that there must be within our reach further and more interesting 

 facts which will illustrate something of the arrangement and mech- 

 anism of this vast system of worlds flying hither and thither through 

 space. 



In outline this is what we shall term the sidereal problem, which 



