108 Prof. Norton on Molecular Physics. 



forces or of heat; and, as we have seen (p. 196), heat is also, in 

 its primary origin, one of the molecular forces. 



Frictional Electricity. — The surface of one body should not in 

 its natural condition exercise any sensible direct electric action 

 upon that of another, unless they are brought into close proxi- 

 mity — certainly much nearer than in any ordinary case of mere 

 contact (see p. 98 and Table I.). When, however, two dis- 

 similar surfaces are pressed together, especially if they are brought 

 within the limits at which a force of adhesion would come into 

 operation, the unequal molecular forces of the dissimilar parti- 

 cles might, as will be seen in another connexion (p. 109), give 

 rise to a polarization of the particles. The development of such 

 polarization should establish a wave movement entirely through 

 the two bodies (p. 101) ; and, as the result, the surface toward 

 which the flow occurred might have an excess of free electricity, 

 while it would be negatively polarized (p. 105) ; that is, the outer 

 envelopes would on the outer side of the molecules have an ex- 

 cess of electricity, and on the inner a deficiency. The reverse 

 would be true of the other surface. This is the probable explana- 

 tion of the electrical excitement which may be obtained in a feeble 

 degree by simple pressure, as in the experiment by Haiiy, of 

 pressing the smooth surfaces of fragments of calcareous spar, 

 quartz, &c. between the fingers. But the process of excitation 

 by friction seems to be different. The most notable distinction 

 to be perceived between the act of rubbing and that of pressure 

 is, that in the former alone the protuberant parts of the two 

 surfaces are pressed against each other laterally. The probabi- 

 lity, then, is that this lateral pressure of the surface-particles is 

 the immediate cause of the development of electricity by the 

 rubbing of one surface over another. Now it is easy to see that 

 this pressure should tend to compress the electric atmospheres 

 of the particles laterally, and so to produce an accumulation of 

 electric aether on their outer sides, and a discharge from thence 

 toward the other surface. If the surfaces be dissimilar in nature 

 or condition, the effects of this sort of action should be unequal ; 

 and the result should be that upon the one surface there would 

 be an excess of electricity, and upon the other a deficiency. 

 The particles of each body, if non-conductors, should also become 

 polarized after the same manner essentially as already explained 

 (p. 100), and in this condition would serve to retain the sur- 

 faces in their disturbed state (p. 104). The explanation 

 here given is sustained by the effect of heat when applied to 

 one of the surfaces, which is to dispose that surface to take the 

 negative state ; and in fact the heat-pulses should expand the 

 molecular atmospheres (p. 277) and tend to produce a discharge 



