VALUE OF THE BRITISH ASSOCIATION UNIT OF RESISTANCE. 30D 
It is not necessary to give the details of the calculations, which have been carefully 
checked. The tabular interval being 6', it was found desirable in many cases to 
proceed beyond the simple interpolation by first differences. The results are 
M(A, a, b) = 215-4674 
M(A+A, a, b) = 205-1917 
M(A— h, a, b) = 226-9835 
M(A, a, b+k) = 2117246 
M(A, a, b—Jc) = 217-5972 
The mean coefficient for the area of the section is found by doubling the first of 
these values, adding in the others, and then dividing by 6. 
Thus 
M = 215-405* 
The separate values allow us to form an estimate of the effect of errors in the 
fundamental data. If we write 
dM . dA db , da 
we may take approximately 
M(A + h, a, b)—Al(A—h, a, b) M 
a=- — - . — — 1 ‘3b 
2h A 
^ In like manner, /x= —*02, whence, since v=-\-2'38. 
Series III. In this case the data remain precisely as before, except that we now 
have 6=15-3472. 
We find 
whence 
M(A, a, b) = 110*9240 
M(A+A a, b)= 111-2573 
M(A— h, a, 6)= 110-2442 
M(A, a, 6+^) = 104-557l 
M(A, a, b-Jc)= 117*6519 
M=110-926 
Determining X, /x, v, as in the former case, we find 
dM dA . db drt 
:= *T "123 ~r~ — *956 — fi-1 *833 * 
M A b a 
From these values, calculated for the circumference of the disc, we have to subtract 
* The factor expressing the number of windings is omitted. 
