of Electrical Discharge, 139 



application of hypothetical formulse as a means of correcting its 

 indications^ is a very unsafe and precarious course. Dr. Riess 

 nowhere proves the application of the doctrines of specific heat 

 to the operation of the instrument, nor does he in any way 

 pretend to show how it operates, except upon an assumption. 

 I by no means question Dr. Riess's analytical calculation, or the 

 skill and ability it displays : I question its applicability to the 

 nature of the experiment. Supposing it should turn out, as is by 

 no means unlikely, that the expansive action is a sort of second- 

 ary action, varying merely with the evanescent efi^ect on the 

 wire, independent of the heating effect, but with which it may 

 have some peculiar connexion, — what then becomes of Dr. Riess's 

 elaborate conclusions ? Franklin, for example, evidently ima- 

 gined that the expansive effects observed by Kinnersley were 

 the result of vapour produced by the shock, or of a sort of smoke 

 emitted by the wires, and so far did not assent to the heat 

 doctrine upon which Dr. Riess now stakes his whole process of 

 research. 



From some interesting experiments instituted since my 

 memoir on this subject appeared, I am led to conclude that we 

 have yet a vast deal to learn relative to the precise operation of 

 this instrument, and that the view I took of it, as depending on 

 the momentary mechanical expansion of a small column of air 

 immediately surrounding the wire, is substantially correct. But 

 until all this be well ascertained, I think it a much safer course 

 to trust to an empirical experimental examination of the imme- 

 diate indications of the instrument, and observe the general 

 laws of its operation by comparison with well-known laws of 

 electricity. Hence I pretend to say nothing about the " neces- 

 sity " or otherwise, of some calculation for rendering " the data 

 capable of comparison/^ 



Now as to my "unit measure," which Dr. Riess treats so 

 slightingly: 1 believe the time is not far distant when he 

 will be compelled in candour to change his opinion upon that 

 question. I have lately submitted to the Royal Society a series 

 of crucial experiments showing the perfect accuracy of this 

 instrument as a measure of quantity, which I believe Dr. 

 Riess will have great difficulty in disproving; nor do I stand 

 alone in my interpretation of this question, however meanly 

 Dr. Riess may profess to think of it ; and I am quite willing to 

 stake the value of the differences existing between Dr. Riess 

 and myself upon the soundness of our respective scientific views 

 of this question alone. 



Faraday, in considering the question of my unit measure, 

 thus expresses himself : " Suppose the unit-jar has about one- 

 tenth the electrical capacity of the large jar, and that being 



