172 Prof. G. Wiedemann on the Laws of the 



to a narrower tube, in whose cross section the number of gas 

 molecules is equal to a, the combined total vis viva in each 

 section still remains the same, because during the same time 

 in both tubes a molecule set in motion meets with an equal 

 number of comparatively quiescent molecules, although the 

 oblique angle at which the gas particles first electrically moved 

 meet others causes the movement to spread, in a direction 

 partly radiating, partly axial, over the entire section. 



This simple transference of motion is accompanied by a 

 partial conveyance of it to the sides of the tube, by which the 

 vis viva of the gas-molecules, and therefore also the tem- 

 perature of the gas, diminishes from the part of the tube 

 nearest to the place of discharge to the furthest. As, how- 

 ever, the lateral spread of the vis viva, in consequence of the 

 excentric impact of the molecules upon each other both in 

 narrow and in wide tubes, whether through more or less 

 concentric strata of molecules, proceeds in the same way to 

 the periphery, it follows that the communication of movement, 

 as well as of heat, to the sides, which is in proportion to the 

 number of the molecules that strike them, must be the same 

 in wider and in narrower tubes. 



As in most experiments this communication of heat is but 

 small, the points furthest from the place of exit of the dis- 

 charge in the shorter tubes are but little cooler than the 

 nearest points, although in longer tubes the cooling is very 

 plainly perceptible by the lesser brightness of the discharge. 



That the passage from the brightly luminous parts of the 

 tube to the darker in such a case follows rather quickly, must 

 be caused by the fact that the brightness of the glow of 

 different bodies, as, for instance, luminous galvanic wires, 

 increases very rapidly with the temperature. 



The opinions stated above agree substantially with our 

 present views upon the constitution of bodies and the conduc- 

 tion of electricity through them. 



I must ask permission here to touch a little more closely 

 upon this subject, as some hypotheses lately put forward con- 

 cerning it appear to me not entirely to agree with ex- 

 perience. 



In solid bodies the molecules vibrate round fixed centres of 

 equilibrium, which are not substantially altered when, in the 

 current, electricity passes from one molecule to another. 

 According to one view this passage occurs by single disruptive 

 discharges. We must then suppose that in some way the mo- 

 lecules of these bodies are united with coverings of particles 

 of electricity, which share more or less in the oscillatory 



