Molecules of JEther contained in Electric Conductors. 191 



Comparing expressions (I.) and (II.), it appears that they 

 differ only by the factor 2enR. And if now we adopt the 

 assumption, certainly favoured by many physicists, that e in the 

 same portion of the conductor is for all currents constantly the 

 same, and therefore the action of different currents in such por- 

 tion differs only by the various values of v, it will be seen that, 

 in the same conductor, expression (I.) is for all currents the same 

 multiple of expression (II.). 



There is, then, only necessary the knowledge of a number 

 which (as one may perhaps dare to say) specifies how often in 

 the unit of time the vis viva of the electric motion (constantly 

 transformed into heat) is reproduced by the electromotive forces, 

 in order from one value of the vis viva to deduce at once the 

 total thermal effect of the current. Perhaps the following con- 

 sideration may elucidate this number. 



Let us imagine from any place in the conductor the resistance 

 and consequently its thermal effect to cease ; from that moment 

 the space of the conductor must be much more filled only with 

 electric fluid, and, indeed, at first of the same density as in the 

 conductor. The electric motion would then be propagated in 

 this fluid without enfeeblement. If we call the constant velocity 

 of propagation of the motion in this case, expressed in millime- 

 tres, C, in 1 second a vis viva certainly not less than the quantity 



s- would arise*. 



n 2 



As starting-point of this entire motion a layer of the conductor 

 of the length y/=- is sufficient, if M denotes the number of mo- 

 lecules of the electric fluid contained in 1 cubic millim. of the 

 conductor, understanding by "molecule" just so much fluid 

 that a translatory motion of it of the sort supposed can be ori- 

 ginated. 



C* 2 



And now, according to the preceding, the value — may 



n 4/ 

 very well be supposed equal to the thermal effect actually accom- 

 plished in the same time, with the action of the resistance, by 



the layer _ . We should then have 



J \/M. 



1 Ce v 1 



e VR. 3 -^=-.|-.9811, 

 x/M n 2 



where the factor 9811 is put because in (I.) the acceleration of 



* It has been already remarked that no account need be taken of further 

 factors in this expression, which at all events would be requisite if oscilla- 

 tions were thought of. 



