330 



SCIENCE 



[N. S. Vol. XXXVI. No. 924 



as the Peltier and Thomson effects, and of 

 radiation and absorption of heat, though 

 in a less satisfactory manner. When ex- 

 tended to give a consistent account of all 

 the related phenomena, it would appear 

 that the number of free corpuscles re- 

 quired is too large to be reconciled, for 

 instance, with the observed values of the 

 specific heat, on the assumption that each 

 corpuscle possesses energy of translation 

 equal to that of a gas molecule at the same 

 temperature. 



Sir J. J. Thomson has accordingly pro- 

 posed and discussed another possible the- 

 ory of metallic conduction, in which the 

 neutral electric doublets present in the 

 metal are supposed to be continually inter- 

 changing corpuscles at a very high rate. 

 Under ordinary condition these inter- 

 changes take place indifferently in all di- 

 rections, but under the action of an electric 

 field the axes of the doublets are supposed 

 to become more or less oriented, as in the 

 Grotthus-chain hypothesis of electrolytic 

 conduction, producing a general drift or 

 current proportional to the field. This 

 hypothesis, though fundamentally different 

 from the preceding or more generally ac- 

 cepted view, appears to lead to practically 

 the same relations, and is in some ways 

 preferable, as suggesting possible explana- 

 tions of difficulties encountered by the first 

 theory in postulating so large a number of 

 free negative corpuscles. On the other 

 hand, the second theory requires that each 

 neutral doublet should be continually eject- 

 ing corpuscles at the rate of about 10 ^° per 

 second. There are probably elements of 

 truth in both theories, but, without insist- 

 ing too much on the exact details of the 

 process, we may at least assert with some 

 confidence that the corpuscles of caloric 

 which constitute a current of heat in a 

 metal are very closely related to the cor- 



puscles of electricity, and have an equal 

 right to be regarded as constituting a ma- 

 terial fiuid possessing an objective physical 

 existence. 



If I may be allowed to speculate a little 

 on my own account (as we are all here 

 together in holiday mood, and you will not 

 take anything I may say too seriously), I 

 should prefer to regard the molecules of 

 calorie, not as being identical with the cor- 

 puscles of negative electricity, but as being 

 neutral doublets formed by the union of a 

 positive and negative corpuscle, in much 

 the same way as a molecule of hydrogen is 

 formed by the union of two atoms. Noth- 

 ing smaller than a hydrogen atom has yet, 

 so far as I know, been discovered with a 

 positive charge. This may be merely a 

 consequence of the limitations of our ex- 

 perimental methods, which compel us to 

 employ metals to so large an extent as 

 electrodes. In the symmetry of nature it 

 is almost inconceivable that the positive 

 corpuscles should not exist, if only as the 

 other end of the Faraday-tube or vortex- 

 filament representing a chemical bond. 

 Professor Bragg has identified the X or 

 y rays with neutral corpuscles traveling at 

 a high velocity, and has maintained this 

 hypothesis with brilliant success against 

 the older view that these rays are not sepa- 

 rate entities, but merely thin, spreading 

 pulses in the ether produced by the col- 

 lisions of corpuscles with matter. I must 

 leave him to summarize the evidence, but if 

 neutral corpuscles exist, or can be gener- 

 ated in any way, it should certainly be 

 much easier to detach a neutral corpuscle 

 from a material atom or molecule than to 

 detach a corpuscle with a negative charge 

 from the positive atom with which it is 

 associated. "We should therefore expect 

 neutral corpuscles to be of such exceed- 

 ingly common and universal occurrence 



