486 Prof. Thomson on the Mechanical Theory of Electrolysis, 



perature of a grain of water from 0° to 1°. Hence, since the 

 unit of force adopted in the measurement of galvanic strength 

 on which the preceding value of € is founded, is that force which, 

 operating during one second of time upon one grain of matter, 

 would generate a velocity of one foot per second, and is conse- 

 quently ^^^ of the weight of a grain at Manchester, we have 



J = 1890x 32-2=44758. 

 Substituting these values for e, 6, and J in (12), we have 

 1 = 2507100 



for the '^intensity ^' or "electro-motive force^^ of a cell of DanielPs 

 battery in absolute measure. To compare this with the electro- 

 motive intensity of a revolving disc such as we have considered 

 (§ 3), let the axis of rotation of the disc be vertical or nearly 

 vertical, and, the vertical component of the terrestrial magnetic 

 force at Manchester being about 9'94, let us suppose that we have 

 F = 10 exactly, which would be the case with a disc exactly hori- 

 zontal in localities a little north of Manchester, and might be 

 made the case in any part of Great Britain by a suitable adjustment 

 of the axis of the disc. Then we have by (11), 



f=5o)r^; 

 or if w be the number of turns per second, 



i=5 X 27rwr2=31-416 x nr^. 

 Hence 



i __ 31*416 xwr^ __ nr'^ 



T "" 2507100 " 79803' 



It appears, therefore, that if the radius of the disc be one foot, 

 it would, when revolving at the rate of one tura per second, pro- 

 duce an intensity ^^^ of that of a single cell of DanielFs, 



and it would consequently have to make more than 79803 

 turns per second to reverse the action of such a cell in the 

 arrangement described in § 4*. We conclude also, that a disc of 

 one foot radius, touched at its centre and circumference by the 

 electrodes of a single cell of DanielPs, and allowed to turn about 

 a vertical axis by the action of the earth upon the current passing 

 through it, would revolve with a continually accelerated motion 

 approaching to the limiting rate of 79803 turns per second, if it 



* Hence in the multiple form of " the new electrical machine " suggested 

 by Faraday, about 800 discs, each one foot in radius, would be required, 

 so that with a rotation at the rate of 100 turns per second about a vertical 

 axis in any part of Great Britain, it might give an intensity equal to that o 

 a single cell of DanicU's. 



