142 Radiant Forces. 



the earth attracts a falling stone, that stone attracts the earth, 

 but if the stone weighs, or is attracted with a force equal to 

 one pound, and attracts or pulls the earth with equal power, 

 the stone falls, and the earth does not visibly or appreciably 

 rise to meet it, because a one- pound pull at the great globe is 

 practically lost in the ponderous mass. 



Electric currents will not traverse the most perfect vacuum 

 we can produce, but light easily traverses any vacuum we can 

 form. Thus we know that it consists of the motion of a more 

 attenuated medium. Gravitation traverses space, and light does 

 the same ; but do they do it in the same way ? In the case of 

 light there is a transmission of the wave form through the 

 delicate matter which seems to fill celestial space. Is gravi- 

 tation in any way dependent for its transmission upon this or 

 upon any other form of matter ? Could it be stopped, as an 

 electric current can be stopped, by taking away the material 

 particles in space ? Or do distant bodies act upon each other 

 with this gravitating attraction without any help from inter- 

 vening materials ? If light be the vibration of ether, its transit 

 must stop if that ether were not present. Does gravitation in 

 anyway present an analogy to light ? or does it stand alone, 

 having some of the properties of a radiant force, and yet con- 

 sisting in no motions, and occupying no space for the trans- 

 mission of its powers ? 



Whenever we come to ultimate questions we enter into the 

 domain of the unknown. We say light consists of the oscilla- 

 tion of ether particles, each one moving in an extremely 

 minute curve, and stimulating its next-door neighbour to do 

 the same, so that a wave is produced. W T e are, however, not 

 in the least degree able to explain why such oscillations of 

 particles should produce on our organs the effects of sight. 

 Wo consider heat as a mode of motion, but we have no idea 

 why a brisk motion of the particles of a candle causes them to 

 burn, or combine with oxygen and give us light. In like 

 manner, if we, reduced gravitation to the category of modes of 

 motion, we could not then understand why two bodies should 

 thereby want to come near each other. Nature is full of these 

 mysteries. We trace her facts, and we note their sequence. Our 

 minds, impelled by will, actuated by design, lead us to appre- 

 ciate the law and order we can discover. We naturally and 

 irresistibly attach to the word cause something more than 

 regular but unconnected sequence. As a result of watching 

 the uniformity of natural operations, we form a conception of 

 inevitable and necessary sequence, and we proceed from inevit- 

 able and necessary sequence to the assumption of a cause suffi- 

 cient to make any sequence inevitable or necessary ; and, failing- 

 to see such cause in the motions of physical particles, we arrive 



