72 THE WORLD-EKERGY 



between ponderable and imponderable matter than modern 

 scientists are for the most part disposed to admit. " Pon- 

 derable " matter is matter that has weight. But weight is, 

 properly speaking, an accident of matter, not a necessary 

 property. It is wholly erroneous to regard it as identical 

 with attraction. It is, as Professor Tait points out, a rela- 

 tion between bodies ; or, as we should here prefer to say, 

 weight is simply the excess of attraction or centripetal 

 force over repulsion or centrifugal force. Even in the 

 ordinary text-books on physics, indeed, it is pointed out 

 that the " weight " of a given body is less at the equator 

 than at any point distant from the equator, and that the 

 greater " weight " always corresponds with greater distance 

 from the equator. Of course this difference in the weight 

 of a body, corresponding with difference in latitude, is due 

 chiefly to centrifugal force that is, to the mass of the 

 body itself combined with, or "multiplied into," the 

 "tangential velocity." And one need only recall the 

 frequently repeated calculation that, were the equatorial 

 velocity increased to seventeen times its present rate, 

 the weight of bodies at the equator would be just nil. 

 That is, even solid bodies would become thus far 

 "imponderable." 



But in another way matter may become imponderable. 

 Weight, as we have seen, is the measure of the excess of 

 attraction over repulsion, or centrifugal force. We have 

 also seen that in respect of the states of matter, the excess 

 of attraction over repulsion is the condition essential to 

 the solid state (the production or retention of matter in 

 the solid state through pressure, being but a special phase 

 of attraction). Thus what we know as "ponderable 

 matter " is directly associated with a large mass of solid 



