418 Prof. B. Threlfall on the Application of the Clark Cell 

 Writing V for ■?, we get 



d\f [V2 7 •§'/].,_ 1 \ G + 7 1 

 hence 



7v 2^ 



Now A/ = when = 0; therefore the arbitrary constant c = 0; 

 and to the order of 6 retained we get 



2 96 



= '207 6 2 + -0269 4 . 



At the extremity of the scale 6 is about J in circular measure; 

 thus at the end of the scale, 



X'= -0233, 



and X = 25'5 scale-divisions. 



Thus on the radius making the angle 0=19° 6', whose 

 circular measure is J, the theoretical curve is outside the circle 

 by a distance of 16 millim. Similarly, when #=10°=-174 

 radius, A/ = '006297, and therefore X = 6*901 scale-divisions 

 =.4*4 millim. 



With these numerical results the curve was laid out on 

 millimetre paper, a template was cut to the curve, and the 

 wooden back of the scale-holder was brought up to the tem- 

 plate. The scale itself was carefully pinned to the wood at 

 short intervals along its whole length. 



The Clark cell supplied with the instrument had the same 

 area of surface as the " large cell " referred to in our previous 

 papers : it was tested from day to day alongside of the large 

 cell, master cell, &c. The following particulars refer to this 

 testing. 



Internal resistance (August 28, 1888), roughly 5*5 ohms. 

 August 29, at 16° C, hospital cell -master cell = -0-000852 

 volt. Terminal E.M.F. hospital cell, two minutes after short- 

 circuiting through 1426 legal ohms, taking E.M.F. of master 

 cell at 1-435:— 



August 28. 1-4263 volt. 

 „ 29. 1-4261 „ 

 „ 29. 1-4262 „ 



About ten minutes after short-circuiting, in each case the 

 E.M.F. fell further '0011 volt. 



