Mr. 0. Heaviside on the Differential Galvanometer. 469 



Table of Diffusion, 

 (Centimetre) 2 



Second 



measure. 



Calculated. 



Observed. 





H &0 



0-7086 

 0-6519 

 0-5575 

 0-1807 

 1427 

 01 386 



0-7214^ 

 6422 | 

 0-5558 [ 

 0-1802 [ 

 0-1409 | 

 01406 ; 

 1-4Q -\ 



Diffusion of matter observed 

 by Loschmidt. 



Diffusion of momentum 

 (Graham and Meyer). 



Diffusion of temperature 

 observed by Stefan. 



Voit. 



Tick. 



i 



H &C0 



H &C0 2 



& CO 



& CO 2 



CO &C0 2 



H 



1-2990 







0-1884 0-213 1 



CO 



0-1748 

 0-1087 



0-212 j 

 0117J 

 0-256 ) 

 1-077 

 0-183 J 

 0-00000365 1 

 03144) J 

 000000116 



CO 2 



Air 



Copper 





Iron 







Cane-sugar in water.. 





(or in a day 





Salt in water 









LXI. On the Differential Galvanometer. 

 By Oliver Heaviside, Newcastle-on-Tyne*. 



npHE great similarity between the systems of resistance- mea- 

 -»- suring by means of the differential galvanometer and 

 Wheatstone's bridge, the latter having been probably suggested 

 by the former, must have struck every one who has had any 

 thing to do with them. In each case do we make one resistance 

 a fourth proportional to three others, and, knowing the three, 

 deduce the fourth. As in the bridge for every resistance to be 

 measured there is a certain arrangement of the three other sides 

 which gives the most sensitive balance, so with the differential 

 galvanometer there must be a best arrangement for any parti- 

 cular case, which it is the object of this paper to point out. 



The expression for the strength of the current through the 

 galvanometer in Wheatstone's bridge is 



E = 



ad— be 



a-\ b -\-c-\-d 



(1) 



J {a + b)(c + d ) I f (a + c)(b + d) A 

 \a + b + c + d J \a + b + c + d J J 



(where v is the electromotive force of the battery, E the current 



Communicated by the Author. 



