H.. A. Rowland—Absolute Unit of Electrical Resistance. 287 
ference is greater than one per cent, we find for the Ohm 
10083 earth quad. 
sec. 
earth quad. 
sec. 
, and when it is less than one per cent, 9966 
, Which is in accordance with the theory, the aver- 
age velocities being 49.2 and 44° nearly. But the individual 
observations have too great a probable error for an exact 
colnparison. Sie 
But whatever the cause of the effect we are considering, the 
following method of correction must apply. e experiments 
show that R is a function of the velocity of rotation, and hence, 
by Taylor's theorem, the true resistance R, must be 
R,=R(1+Aw+Bw?-+ &c.), 
and when R is the mean of results with positive and negative 
rotations, 
R,=R(1+Bu?+Du!+&c.). 
Supposing that all the terms can be omitted a the first 
two, and using the above results for large and small velocities, 
we find R, = 9926 =e But if we reject the two results 
in which the difference of positive and negative rotations is 
over seven per cent, we find 
R,="9034 sahanns, 
The rejection of all the higher powers of w renders the cor- 
rection uncertain, but it at least shows that the Ohm is some- 
what smaller than it was meant to be, which agrees with my 
ex periments. : : 
t is to be regretted that the details of these experiments 
have never been published, and so an exact estimate of their 
value can never be made. Indeed, we have no data for deter- 
mining the value of the Ohm from the experiments of 1863. 
All we know is that, in the final result, the 1864 experiments 
had five times the weight of those of 1868, and that the two 
results differed ‘16 per cent, bat which was the larger is not 
stated. Now the table of results published in the report of the 
1864 experiments contains many errors, some of which we can 
find out by comparison of the columns. The following cor- 
rections seem probable in the eleven at 
fifth columns, read 1:0032 and +082 in place of 1-0040 an 
+0-40. No. 11, fourth and fifth columns, read 10065 = 
+0°65 in place of 09981 and —0'19. Whether we make 
