DR. EVERETT ON THE RIGIDITY OE GLASS. 
151 
Hence we have the following means : — 
1 (a) (b). Torsion 25-78 Flexure 19-71 
2(a) (b). „ 25-86 „ 19-70 
3 (a)(b). „ 25-86 „ 19-72 
And applying the correction for difference of scale-divisions, which is now 1 part in 266 
T t 
to be subtracted from p> we have as the values of Poisson’s ratio, or p — 1, 
•303, -308, -306, giving a mean of -306. 
The mean values of T and F are respectively 25-83 and 19-71, which reduced to cen- 
timetres become 3-61 and 2‘76 ; and as twice the height of the scale is 447, Ave find the 
amounts of torsion and flexure respectively in the portion of rod between mirrors, to be 
about -00808 and -00617. The values of 6 are -ff-f- of these, or -00993 and -00758, 
which are to be multiplied by *729, as before, giving for the mechanical corrections the 
values 
+ •0072 T and +-0055 F. 
No measurements were made to determine the optical corrections, we shall therefore 
assume them to be the same as in the experiments on the brass rod, viz. 
-•0025 T and --0013 F, 
making the total corrections 
+ •0047 T and +-0042 F, 
T 
whose difference is so small that the correction for p may be neglected. We therefore 
adopt for Poisson’s ratio, as determined by these experiments, the above value -306. 
The corrected mean values of T and F are 25-95 and 19-79, and we have 
£=447-0 x 100 x 55-77 x 38 1 5 x aWs -s-T, 
/= 447-0 x 100 x 55-77 x 38-15 x 
whence 
log £=9*83317- logT=7-41903, 
log/=9-83153- logF=7-53508. 
The weights in air and water were respectively 132-94 and 116-00 grms., the tempera- 
ture of the water being 7'7 XL, and the length of the portion weighed being 38*1 centhns. 
The correction for density at this temperature may be neglected, and we have volume in 
centim. = loss of weight in grammes =16*94. Hence wr 2 =^v ] 4 = -44462 r=*37620. 
M=^j =2,179,300,000, 
n 
l 
<7 
= ~= 834,120,000, 
~3(3tt^M) = 1>875,600,000, 
= ^—1 = -306, as above ; 
x 
