368 
ME. EVERETT ON THE RIGIDITY OF IRON AND COPPER. 
Hence we find 
Torsion in portion of rod between mirrors . . . *0114, 
Flexure „ „ „ „ . . . -0083, 
which numbers being multiplied by ffy X '729 give -0132 and -0096. Hence the me- 
chanical corrections are 
+ -0132 T and + -0096F, 
which being added to the optical corrections already specified, give the total collections 
+ •0085 T and +-0055F, 
rn 
and a resultant correction +’003 d. The application of this correction gives as the 
JP 
corrected determinations of <r, -378, - 376, and *379, and we adopt the mean *378. 
The corrected values of T and F are 368*5 and 266*4. 
For the torsional and flexural rigidities, we have 
£=445-6 X 100 X 55 77 X 28-72 x UH ^T, 
/= 445-6 X 100 x 55-77 x 28-72 x JtfI? 
Hence 
log £=9-70850- logT=7T4206, 
log/= 9-70686 — logF=7-28133. 
The rod having been cut at the places where the mirrors were attached, the middle 
piece was found to weigh 110-645 in air, and 98-136 in water at temperature 10° C. 
The expansion of water at this temperature being 1-00026, we have for the volume of 
the piece 
12-502xl'00026 = 12-5122; 
and for its specific gravity, 
110-645 -r 12-5122 = 8-84293. 
The volume divided by the length, which was 28-61, gives 7ir 2 = *43733, r=*37310. 
TTpiipp 
M=l, 255, 800, 000, 
n = 455,640,000, 
Tc =1,716,400,000, 
<r = -378, 
the units of length and force being the centimetre and gramme weight. 
The values of n obtained by Sir W. Thomson, for brass and copper from observations 
on the torsional vibrations of wires * were, in , millions of grammes weight per square 
centimetre, 
Brass, three specimens .... 410-3 354-8 350-1 
Copper, two specimens .... 448-7 448-4. 
Other specimens of copper in abnormal states gave results ranging from 393-4 to 472-9. 
* Proceedings, Royal Society, May 18, 1865. 
