194 Loomis — Effects of Changes of Temperature, etc. 



subtracting thetn in order to obtain a small difference. In the 

 method employed in this research the quantities measured 

 differed but little in size from the quantities desired, and much 

 greater accuracy was easily obtained. 



The following is suggested as the explanation ; Prof. Ewing 

 lias recently made an important addition to Weber's theory of 

 magnetism, in claiming that the forces which hold the little 

 molecular magnets in position are largely the mutual attractions 

 and repulsions of these molecular magnets among themselves. 

 In applying E wing's theory to the case in hand let us con- 

 sider a row of magnetic molecules ABO, etc. 



ABC HIJKL 



J is held in position by the action of H,I, etc. on the one side 

 and K,L, etc. on the other side, while A has only B,C, 

 etc. to act upon it. It is evident that the force holding J in 

 position is greater than that acting on A. Suppose the bar of 

 which this line of molecules is a part is heated. If in this 

 process the energy of vibration of A and J receive equal incre- 

 ments, it is evident that the increase in the amplitude of vibra- 

 tion of A will be greater than that of J. The magnetic moment 

 contributed by each molecule is the moment of the molecule 

 resolved along the direction of magnetization of the bar. The 

 moment contributed by A. would therefore suffer a larger pro- 

 portional loss on heating than that contributed by J, and so the 

 loss would be greatest at the ends. This explanation will also 

 account for the fact that the proportional change in magnetic 

 moment is greater in short magnets, because in short magnets 

 the end regions of these lines of molecular magnets will natur- 

 ally form a larger part of the whole line than in long magnets. 

 We should also expect these lines of molecular magnets to be 

 longer when the intensity of magnetization was greater. This 

 would account for the fact that the change in magnetic moment 

 due to temperature changes is less the greater the intensity of 

 magnetization. This appears from the curve given in fig. 1. 

 There are other facts which point in the same direction : When 

 a magnet is heated before it has reached the permanent state, 

 Kupfer found, as already stated, that the proportional perma- 

 nent loss was greatest at the ends. In some rough tests I have 

 made on this point, heating the bar almost to redness, I have 

 found the permanent proportional loss at the ends nearly twice 

 as great as at points near the center of the magnet. This 

 would naturally follow from Ewing's theory, for the force 

 holding the end magnetic molecules in position being less, they 

 would be more easily set into such violent vibration as to swing 

 out of one position of equilibrium into another. 

 Western Springs, 111. 



