250 Dr. J. Croll On the Transformation of Gravity. 



mation is a change from one form to another. Tliere is first 

 the one t'onu. and then the oilier ; or, in other words, there is 

 firsi the one form, and afterwards the other. The two are not 



simultaneous. It becomes the one by ceasing to be the other. 

 Transformation without lapse of time is both inconceivable and 

 a contradiction in terms. 



If we leave out of consideration mental phenomena, we may 

 affirm that transformation of energy without transposition in 

 space is just as impossible as transformation of energy with- 

 out transposition in time ; only it is not so directly obvious in 

 the one case as in the other. That transformation of energy 

 necessarily implies change of position in space may be 

 proved from general considerations alone, without reference 

 to special cases. 



Transformation of energy must consist either (1) of change 

 of potential energy into kinetic, or (2) of kinetic energy into 

 potential, or (3) of one form of kinetic energy into another 

 form of kinetic energy, or (4) of one form of potential energy 

 into another form of potential energy. There can be no other 

 form of transformation beyond these ; for they comprehend the- 

 whole field of the possible. Now it is obvious that the first 

 three forms of transformation imply change of position in 

 space ; for kinetic energy implies motion in some form or 

 other, and motion implies change of position in space. The 

 fourth and last form of transformation, viz. of one form of 

 potential energy into another, were it possible, might, it is 

 true, be conceived to take place without change of position ; 

 but there is evidently no such thing in nature, so far as is yet 

 known, as one form of potential passing directly into another 

 form. It is true that the potential energy of one form may 

 be transformed into potential energy of another form ; but it 

 must, in the first instance, become ldnetic before it assumes 

 the second form. Static electricity, for example, may be 

 transformed into magnetism, but not so directly. It must 

 first assume the dynamic form before it can become magnetism. 

 A magnet will magnetize a piece of soft iron, but before the 

 iron assumes the magnetic or potential state a molecular 

 change takes place. The first effect produced on the mole- 

 cules of the iron is dynamic before they assume the static or 

 magnetic state. 



The conclusions to which we are led may be stated as 

 follows : — 



1st. Under every possible circumstance time and space are 

 absolutely necessary as conditions to the transformation of 

 energy from one form to another — the physical reason being 

 that there can be no transformation without motion, and there 

 can be no motion without time and space as conditions. 



