NEW CONCEPTIONS LN SCIENCE 



of a candle and the consuming heat of the sun, the 

 invisible rays from the Crookes tube which lend a 

 pale phosphorescence to a screen, and the huge elec- 

 tric-waves which transmit signals from Cornwall 

 to Cape Cod, should all reach the same distance in 

 the same flash of time. The speed of light and its 

 kindred is at present the swiftest thing known. It 

 may be there is nothing swifter, and can be nothing. 

 The only speck on the horizon that seems at the 

 moment to contain possibilities which might upset 

 this conclusion is the question of gravity. As to the 

 rate of action of gravity we have no notion what- 

 ever. Its effects are not screened by any sub- 

 stance, and if, therefore, it is a mode of motion, we 

 have no way of measuring it. When the moon 

 comes between the earth and sun, the pull of the 

 sun is simply added to the pull of the moon. 

 The one in nowise influences the other. Gravity 

 has more of the allure of something infinite than 

 anything we know of. Yet the strength of its 

 action is expressible in the simplest of equations. 

 Newton's law of inverse squares was, indeed, the 

 first found of the great physical constants of nature. 

 So far as we know this force is universal. Trusting 

 implicitly in the truth of this, astronomers weigh 

 the sun, the planets ; they even calculate the mass of 

 dark stars whose existence is but an inference from 

 the observed motion of others. It was by the 



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