﻿202 Mr. J. Croll on the Physical Cause 



The correctness of the above conclusion, that the weight of the 

 ice is not a sufficient cause, depends upon the truth of a cer- 

 tain element taken for granted in the reasoning, viz. that the 

 shearing -force of the molecules of the ice remains constant. If 

 this force remains constant, then Canon Moseley's conclusion is 

 undoubtedly correct, but not otherwise ; for if a molecule should 

 lose its shearing-force, though it were but for a moment, if no 

 obstacle stood in front of the molecule, it would descend in virtue 

 of its weight. 



The fact that the shearing-force of a mass of ice is found to 

 be constant does not prove that the same is the case in regard 

 to the individual molecules. If we take a mass of molecules in 

 the aggregate, the shearing-force of the mass taken thus collec- 

 tively may remain absolutely constant, while at the same time 

 each individual molecule may be suffering repeated momentary 

 losses of shearing-force. This is so obvious as to require no further 

 elucidation. The whole matter, therefore, resolves itself into this 

 one question, as to whether or not the shearing-force of a crys- 

 talline molecule of ice remains constant. In the case of ordinary 

 solid bodies we have no reason to conclude that the shearing-force 

 of the molecules ever disappears, but in regard to ice it is very 

 different. 



If we analyze the process by which heat is conducted through 

 ice, we shall find that we have reason to believe that while a mo- 

 lecule of ice is in the act of transmitting the energy received (say 

 from afire), it loses for the moment its shearing -force if the tempe- 

 rature of the ice be not under 32° F. If we apply heat to the end 

 of a bar of iron, the molecules at the surface of the end have 

 their temperatures raised. Molecule A at the surface^ whose 

 temperature has been raised, instantly commences to transfer to 

 B a portion of the energy received. The tendency of this pro- 

 cess is to lower the temperature of A and raise the temperature 

 of B. B then, with its temperature raised, begins to transfer the 

 energy to C. The result here is the same ; B tends to fall in tem- 

 perature, and C to rise. This process goes on from molecule to 

 molecule until the opposite end of the bar is reached. Here in 

 this case the energy or heat applied to the end of the bar is 

 transmitted from molecule to molecule under the form of heat or 

 temperature. The energy applied to the bar does not change its 

 character ; it passes right along from molecule to molecule under 

 the form of heat or temperature. But the nature of the process 

 must be wholly different if the transference takes place through 

 a bar of ice at the temperature of 32°. Suppose we apply the 

 heat of the fire to the end of the bar of ice at 32°, the molecules 

 of the ice cannot possibly have their temperatures raised in the 

 least degree. How, then, can molecule A take on, under the form 



