CHAP. XI.] ELECTRICAL STANDARDS, ETC. 337 



Determine its potential when charged, and measure the 

 charge of discharge through a galvanometer. 



2d, Thomson's. Find the electromotive force of a 

 battery by electromagnetic methods, and then weigh the 

 attraction of two surfaces connected with the two poles. 



3d, (Not tried, but talked of by Jenkin). Find the 

 resistance of a very bad conductor in both systems 



(1) By comparison with (4th June), 



(2) By the log. decrement of charge per second. 



All the methods require a properly graduated series 

 of steps. The 1st and 2d determine V, a velocity = 

 310,740,000 meters per second. 



The 3d method determines V 2 . 



The first method requires a condenser of large capacity, 

 and the measurement of this capacity and that of the dis- 

 charge by a galvanometer. 



I think this method looks the best ; but I would use a 

 much larger condenser than Weber, and determine its capa- 

 city by more steps. 



The chief difficulty of Thomson's method is the measure- 

 ment of a very small force and a very small distance. I 

 think these difficulties may be overcome by making the 

 force act on a comparatively stiff spring and magnifying 

 optically the deflection. 



On the third method we require a very large condenser 

 indeed, also a series of resistances in steps between 4th June 

 and that of the insulating substance of the condenser, and a 

 galvanometer (or electrometer) to measure discharge (or 

 tension). . . . 



To C. H. CAY, Esq. 



8 Palace Gardens Terrace, 

 18th November 1863. 



We hope to hear how you are. A little literature helps 

 to chase away mathematics from the mind. I have read 

 Paracelsus in parts, but concluded that there was a great deal 

 of poetry in it ; but Mr. Browning has written much better 

 poems with half the quantity of poetry at his disposal. 



z 



