1 10 On the condition of the Molecules of Solids, 



electricity, partially to effect our purpose. Under the influence 

 of these . forces, do bodies behave as our theory requires ? In 

 Prof. TyndalFs work on Heat*, an interesting experiment is 

 described which shows that a body between the poles of a pow- 

 erful magnet can be moved only with some difficulty, the resist- 

 ance experienced being exactly as though it were immersed in a 

 viscous body. Anyone who has handled a revolving gyroscope 

 must be struck with the great similarity of its resistance. The 

 more powerful the magnet, the greater is the effect experienced ; 

 and doubtless if we could perfectly polarize a body, it would be 

 impossible to move it save by molecular force. It is to this ex- 

 periment, described so ably by Prof. Tyndall, that I am indebted 

 for this mode of proof. But there is no need of such costly ap- 

 paratus to prove the point; the resistance of the keeper of a 

 common magnet, the attractions and repulsions of magnets and 

 electrified bodies are examples of the fact that a polarized body 

 is, while in this condition, comparatively independent of external 

 force in the ratio of its polarization. But we may go further, 

 and ask to what is this polarizing effect due ? Each pole of a 

 magnet attracts or repels ; consequently the effect of the two on 

 a molecule between them similarly affected by each is that of a 

 couple, causing it to rotate on an axis equatorially situated. 

 Each molecule, then, within the sphere of action rotates in a plane 

 the resultant of its original one and that induced by the magnet. 

 When the magnet is withdrawn, they revert to their own planes. 

 "When only a single pole acts, rectilinear motion ensues, and the 

 body is attracted or repelled. With the nature of this directive 

 force we are not now concerned, though it seems probable that 

 magnets are bodies whose atoms are permanently polarized, i. e. 

 whose molecular axes are parallel, and which induce the same 

 state in other atoms, just as the pendulums of neighbouring clocks 

 influence one another. But many other facts imperatively demand 

 such an hypothesis as that under consideration — e. g., the heat 

 caused by impact. For how can collisions between molecules be 

 so violent, how can they clash with such mechanical results as they 

 do, unless they are moving with immense velocities so as to cause 

 their momentum to be immense ? These effects have been well 

 delineated in the work to which reference has already been made. 

 Indeed all the phenomena of heat prove that the molecules of 

 solids are in motion, while such considerations as their chemical 

 inactivity, and their unequal transmission of pressures, prove that 

 they possess no lateral motion, consequently it must be a motion 

 of rotation round their own axes. A simultaneous vibratory 

 motion of the particles, though of itself insufficient to account 

 for the facts under consideration, is not inconsistent with them. 

 * Heat considered as a Mode of Motion, p. 35, ed. 1. 



