192 POPULAR SCIENCE MONTHLY. 



spell over that hazy cloud of Pleiads, binding them, like ourselves, 

 with bonds indissoluble? Who shall answer, yes or no? We can only 

 say that astronomers have as yet but stepped upon the threshold of 

 the universe, and fixed the telescope's great eye upon that which is 

 within. 



Let us then begin by reminding the reader what is meant by that 

 Newtonian law of gravitation. It appears all things possess the re- 

 markable property of attracting or pulling each other. Newton de- 

 clared that all substances, solid, liquid or even gaseous, from the 

 massive cliff of rock down to the invisible air — all matter can no more 

 help pulling than it can help existing. His law further formulates 

 certain conditions governing the manner in which this gravitational 

 attraction is exerted; but these are mere matters of detail; interest 

 centers about the mysterious fact of attraction itself. How can one 

 thing pull another with no connecting link through which the pull 

 can act? Just here we touch the point that has never yet been ex- 

 plained. Nature withholds from science her ultimate secrets. They 

 that have pondered longest, that have descended farthest of all men 

 into the clear well of knowledge, have done so but to sound the depths 

 beyond, never touching bottom. 



This inability of ours to give a good physical explanation of gravi- 

 tation has led numerous paradoxers to doubt or even deny that there 

 is any such thing. But fortunately we have a simple laboratory ex- 

 periment that helps ns. Unexplained it may ever remain, but that 

 there can be attraction between physical objects connected by no visible 

 link is proved by the behavior of an ordinary magnet. Place a small 

 piece of steel or iron near a magnetized bar, and it will at once be so 

 strongly attracted that it will actually fly to the magnet. Any one 

 who has seen this simple experiment can never again deny the possi- 

 bility at least of the law of attraction as stated by Newton. Its 

 possibility once admitted, the fact that it can predict the motions of 

 all the planets, even shown to the minutest details, transforms the possi- 

 bility of its birth into a certainty as strong as any human certainty can 

 ever be. 



But this demonstration of Newton's law is limited strictly to the 

 solar system itself. We may indeed reason by analogy, and take for 

 granted that a law which holds within our immediate neighborhood is 

 extremely likely to be true also of the entire visible universe. But 

 men of science are loath to reason thus; and hence the fascination of 

 researches in cosmic astronomy. Analogy points out the path. The 

 astronomer is not slow to follow; but he seeks ever to establish upon 

 incontrovertible evidence those truths which at first only his daring 

 imagination had led him to half suspect. If we are to extend the 

 law of gravitation to the utmost, we must be careful to consider the 



