Trowbridge and McRae—Elasticity of Ice. 351 
Experiment I.—Jan. 29, 1885. 
1=33'cm. r=-77 em. $= 886 n=—54‘15 
E=66 165" 
Experiment IT. ~Jan, 31, 1885, 
=35'cm r= 90cm 8 = °886 n= 514 
“ E= 55 & 10°, 
Transverse Deflection. 
We next went to a neighboring pond aud sawed rectangular 
beams of ice and made measurements upon their elasticity at 
the pond. Two boards about 20 em. wide and 60 em. long 
were laid upon the ice. Two half cylinders of wood were 
placed upon these to form the supports for the beams. The 
athetometer rested upon a board 30 em quare_ placed 
Upon the ice. It read to fiftieths of a millimeter. After th 
*xperiments the part of the scale used was compared with a 
‘tandard centimeter, made by Prof. W. A. Rogers of the Har- 
vard Observatory, and each millimeter was found to be not 
More than -2™™ jn error, so the readings were not corrected. 
A vertical rod with a needle at the top was inserted in a boar 
5 om, Square and served as an index. ‘The index was placed 
on the middle of the beam and the weights were arranged 
‘YMmetrically on each side. 
€ ice was 23 cm. thick, had no cracks or fissures and 
semed to be free from air bubbles. There were about 
8 cm. at the bottom which appeared to be of a later forma- 
ton than the rest, it was therefore sawed off. 
Care was taken to have all the apparatus below zero before 
the ®Xperiments began so as not to melt the ice. The wind 
vas very light all day and did not shake the index. The 
"sults are given in tables I and II. 
Che difference in the modulus of the same bar with the same 
"eight at different times may in part be due to slight variations 
the positions of the weights, The index was simply place 
°n the beam and may have been jarred by putting on or taking 
off the weights, although as much care as possible was taken to 
Oi 
ae and after the weights were on. v 
on is used in calculating H’ and the return deflection H. 
