148 
DR. EVERETT OX THE RIGIDITY OF GLASS. 
and the second optical correction is still inappreciable. We have therefore as the total 
corrections to be applied 
+ •0142 T, +-0101 F„ +-0125 F 2 , 
T T . T T 
from which we deduce for |r and j|r the corrections +-0041 jr and + ‘0017 jp-- 
Hence the corrected values of Poisson’s ratio are — 
From T and F, . . . -457, -467, -471, -474, -465, -467, 
From T and F 2 . . . -476, *467, *476. 
The mean of these nine values is ‘469, which we therefore adopt as the value of a for brass, 
being nearly double of our value for glass. The comparison of our results for these two 
substances with those of other experimenters is somewhat startling. It stands thus : 
Glass. Wertheim, -33, Maxwell, -332, Everett, -239, 
Brass. Kirchhoff, *387, „ -469; 
and our two results, -239 and -469, were obtained with the same apparatus in the same 
position, each of them being the mean of several determinations, which for glass ranged 
from -223 to -241, and for brass from -457 to *476. 
The following are the values, uncorrected and corrected, of T and F, the latter 
including botli Fj and ^F 2 . 
Uncorrected. Corrected. 
T. 
F. 
T. 
F. 
I («)(*). 
406-0 
278-0 
411-8 
280-8 
II (a)(b). 
405-0 
275-5 
410-7 
278-3 
HI («)(*)• 
405-5 
275-1 
411-3 
277-9 
1 (a)(b). 
408-1 
276-5 
413-9 
279-3 
2(a)(b). 
407-0 
277-5 
412-8 
280-3 
3 («)(*)• 
407-0 
277-0 
412-8 
279*8 
1 («)(*)• 
f275-6 
279-0'| 
2 (a)(b). 
<276-2 
279-7 Uf 2 
3 («)(*)• 
(274-9 
278*3 J 
Means of corrected values . 
. 412-2 
279-3 
The elements for deriving t from T, and /’from F, are the same as for the glass rod, 
except that the length between mirrors is 24 - 54 instead of 23*56. 
We thus find 
log £=9-67439— logT=7-05928, 
log/=9-67209-logF=7-22602. 
To determine the radius r of the rod, we have weight in air=9P361, weight in water 
= 80-578, the temperature of the water being 7-3 E. Hence volume in centimetres 
=10-783 X 1-0002=10-785, which, being divided by the length 24-54, gives wr 2 = -43949. 
