770 
PROFESSOR O. REYNOLDS ON CERTAIN DIMENSIONAL 
The apparatus as arranged is shown in fig. 9, Plate 47. 
The tube having been dried was filled with dry air at the pressure of the atmosphere. 
A hot body was then brought near it. 
In order to secure uniformity in the hot body, a test tube filled with boiling water 
was placed on a stand, which stand remained in the same position throughout the 
experiment, the water in the test tube being boiled the instant before the tube was 
placed on the stand. 
The motion of the fibre was then watched through the microscope and measured. 
Having ascertained the motion, the heater w r as removed and the fibre allowed to 
return to its normal position, which it always did with more or less exactness. 
The tube was then exhausted to a limited extent and the operations repeated. 
48. In this way were obtained a series of observations both for air and hydrogen 
at various pressures. These are shown in the following tables. 
Table XVIII.—Impulsion of fibre of silk in air, August 1, 1878. 
Pressure by 
vacuum gauge. 
Motion of the 
fibre. 
inches. 
inches. 
30 
-•0930 
16 
-•0300 
8 
+ 00 
4 
+ •0150 
2 
+ ■0210 
i 
+ -0230 
■5 
+ •0390 
*2 
+ -0700 
■I 
+ •0830 
•05 
+ -0930 
•025 
+ •1005 
Table XIX.—Impulsion of fibre of silk in hydrogen, August 1. 1878. 
Pressure by 
vacuum gauge. 
Motion of the 
fibre. 
inches. 
inches. 
30 
+ -0040 
16 
+ ■0070 
8 
+ •0100 
5 
+ ■0160 
2 
+ •0310 
1 
+ -0490 
•40 
+ •0710 
*2 
+ ‘0880 
•i 
+ •1070 
Table X\ III. shows that with air the result was negative until a pressure of less 
than 8 inches was obtained, it then became positive, and it was measurable at a 
