288 H. A. Rowland—Absolute Unit of Electrical Resistance. 
' With the corrections the mean value of the 1864 experiments 
is 1 Ohm = 1-00071 St auae’ 
fourth column, it is 100014. With the corrections the dif 
ference between fast and slow rotation is ‘6 per cent. 
, and without them, using the 
being one formed out of a combination of Weber’s two methods 
of the earth inductor and of damping, by which the constant of 
the galvanometer was eliminated, and is the same as Weber 
used in his experiments of 1862. His formula for the resist- 
ance of the circuit, omitting small corrections, is 
_ 3282T?2,(A—A,) AB 
= ?K (A2--B?)? 
where S is the surface of the earth inductor, T is the bori- 
zontal intensity of the earth’s magnetism, K the moment of 
inertia of the magnet, ¢, the time of vibration of the magnet, 
A the logarithmic decrement, and A and B are the ares in the 
method of recoil. 
an 
wv 
approximately, 
wire occupied two per cent of the radius of the coil, making it 
uncertain to what point the radius should be measured. As 
the coil is wound, each winding sinks into the space between 
the two wires beneath, except at one spot where it must pass 
it would diminish the value of S? 1:4 per cent, and make 
Kohlrausch’s result only °6 per cent greater than the result of 
the British Association Committee. ~ 
‘Three other quantities, T, A and K, are very hard to deter- 
mine with accuracy, and yet T enters as a square. It is to 
