COMPRESSIBILITY OF GLASS. 597 
TABLE III.—Summary of Experiments made on the 3d, 4th, and 7th June 1880, 
on the Compression produced on a Glass Rod by Pressures up to 240 
Atmospheres. 
i 38 Z 3 Ag Linear Compression. E 5) 3 a re 2 A : 
2) EE | 52 | 22 | ince, | ye [pemimin| 2858 | 2229 | Bees 
a | ZO HO ax ; Million. | per Atmo. | OF2—q | SQaea | 56Q as 
100Q 
uh P F H K N Q Tess 
R 
1 8 13°5°| 64 0:0047 62°6 0:98 30 0:00047 | 10-0 
6 il 12°2 | 109 0:0075 100 0:92 2°8 44 58 
2 8 ice ay al a 0:0083 110 0:94 2:9 34 4-1 
7 10 12sSe) Loe 0:0113 150 0:96 2°9 42 3 
3 13 NAHSS Wy IUSys) 0:0112 149 0:95 2:9 56 5:0 
4 Sree to Le 0:0133 178 1:00 30 42 oe 
8 7 135) || USI) 0:0140 187 0:96 2°9 33 2°3 
5 10 N25: | U9 0:0148 197 1:00 3°0 46 Syl 
Si oti) 12°8 | 216 0:0155 206 0:96 2°9 58 af 
10 6 12:9 | 240 0:0167 223 0:93 2°8 59 3°5 
0-960 2:92 
Two columns Q and R are added. Q gives the greatest absolute deviation 
from the mean total expansion in any series, R gives the deviation per cent. 
In the observations recorded I made no attempt to subdivide the micro- 
meter divisions further than to estimate a half. As the micrometer readings 
are not affected directly by the pressure, the deviation per cent. should be, as 
it is, less the higher the pressure ; and there is no doubt that the higher the 
pressure is the greater is the accuracy of the observation. The only way in 
which the pressure affects the reading of the micrometer is that when it is 
sufficiently high it produces a microscopic distortion of the tube, which throws 
the point of the rod very slightly out of focus. This is remedied by a slight 
touch of the fine adjustment screw of the microscope. 
The general result of these experiments is that the linear compressibility of 
the glass experimented on is 0°96, and its cubical compressibility 2°92 per 
million. 
GRASSI* gives as the means of his observations at pressures up to ten 
atmospheres—Glass, 2°25; crystal, 2°804 and 2°8584. The agreement between 
the two is very close. 
* Ann. Chim. Phys, (1851) [3], 31, p. 474. 
VOL. XXIX. PART IL. Gel 
