258 
DR. J. YOUNG AND PROFESSOR G. FORBES ON THE 
Also from § 6 of the mathematical theory the first approximation to the value of 
^, T . n + n' 
2N b is - 
log (n+n) .2-9444922 
logr.1-0791812 
r2N B =73,350 . 1-8653110 
[first approximation 
<7=1-08181 . -0341510 
r2^N B =79-3345 . 1*8994620 
[first approximation 
These are the values which are adopted in calculating the second term in the 
following reductions. 
The rejection of observations .—We resolved never to reject a single observation 
simply because it differed largely from our average result. The only cases where we 
rejected an observation were (1) when there was no corresponding observation of the 
next equality taken at a very short interval of time, and (2) when the traces made by 
the clock pen on the chronograph showed great irregularities in the second differences, 
or when they showed that the friction on the axle was abnormally great. 
With reference to No. (1) we may state that a quarter of an hour even might alter 
the value of p by fog, &c., and this would invalidate the result. 
With reference to No. (2) it is right to say that we generally read off a large 
number of clock-pen marks corresponding to each observation. From these we could 
easily judge if the chronograph was working well. 
