1 68 THE BORDERLAND OF SCIENCE. 



It is, in the first place, a surprising circumstance 

 that the stars should travel so swiftly as they do, amid 

 the depths of space. We do not here speak of this 

 circumstance as surprising merely in the sense in 

 which so many astronomical facts are surprising. It 

 is startling to consider that Sirius is more than a 

 thousand times more massive than our sun, or that the 

 sun is more than a million times larger than the earth 

 on which we live. But there is nothing in these or 

 similar facts, which is not in accordance with our ideas 

 respecting the constitution of the universe. The 

 rapid motions of the stars, however, present a source 

 of grave perplexity, in the circumstance that motion is 

 a measure of force, and we cannot understand what the 

 force can be which has produced these motions. The 

 mutual attractions of the stars are utterly unequal to 

 the generation of velocities so enormous. The stars 

 which are the next neighbours of any given star are 

 those which tend most effectually to excite motion in 

 that star ; and their attractions counteract each other 

 because acting in different directions. But supposing 

 all these stars removed to one side of the first, so as to 

 combine their attractions upon it, even then, at the 

 enormous real distances separating the stars from each 

 other, the resulting motions would not be comparable 

 with those which actually exist. Thus we have, in the 

 motions of the fixed stars, the evidence of a mighty 

 force other (it would seem) than gravity, and perhaps 

 acting according to other laws. 



Now, if the assumed explanation of the rapid 



