﻿Intelligence and Miscellaneous Articles. 239 



cumstances yields sparks of 15 inches. Here also the quantity of 

 electricity was almost proportional to the velocity of rotation ; 

 for — 



Velocity of rotation . . . . =-J \ \ f- 



Deflection =9'7 14*7 26-7 40'5 



Calculated =9*2 137 27'5 41*2 



As both machines can be turned with the same velocity, Holtz's 

 is more productive in the ratio 10:3. 



In reducing the current to absolute magnetic measure, the deflec- 

 tion must be multiplied with 0*00000251. Owing to agitations, the 

 greatest velocity observed, of three turns in two seconds, would be 

 almost the maximum for continuous use with the above machine. 

 If instead of the deflection 137 we take as the maximum 150 divi- 

 sions, the intensity of the current in magnetic measure is 



150x0-00000251 = 0-000376. 



Changed into mechanical measure, we have 



0-000376 x 155370 xl0 6 =58 million 



units of positive electricity in a second, or a little more than one 

 charge of the small Leyden jar used in the measurements of Weber 

 and my father. 



Yet how small this quantity is as compared with that set in mo- 

 tion by voltaic currents is seen from the fact that the current s 0003 7 6 

 only decomposes — — — of a milligramme of water, or that, in order 



to obtain a cubic centimetre of explosive mixture, the strongest cur- 

 rent of our electrophorus machine would have to be passed for about 

 forty hours through water. 



I have incidentally foun d the electromotive force of a Grove's ele- 

 ment in absolute measure to be =17*9, assuming the magnetic as 

 unit of current- intensity, and Siemens's as unit of resistance. H. 

 von Waltenhofen* finds, expressed in the same unit, Daniell=H*4 ; 

 and Bosscha in the same manner finds Danielle 10*8; from which 



Grove 



pj — — -. = 1"57 or 1*66 respectively, which is about the number ob- 

 tained by direct comparison. The current 0-000376 of our ma- 

 chine is therefore produced by a single Grove's element in a conduc- 

 tion of 17 ' 9 , =48000 mercury-units, or in a telegraphic com- 

 o-ooo3/6 - s r 



munication of about 3S00 miles. 



To obtain an idea of possible medical or physiological applications, 

 I determined the resistance of the human body, which from hand to 

 hand (the hands being immersed in dishes containing liquid) in four 

 persons amounted to between 1600 and 3600 mercury-units, the 

 mean being 2200. Putting the polarization as equal to the electro- 

 motive force of one Grove's element, which for feeble currents is far 

 too high, a battery of two elements would furnish the current 



* Pogg. Ann, vol, cxxxiii. p, 462. 



