THEEMAIj effects of fluids in motion. 
331 
of heat exists besides that from stopped air. It is also evident that, as the velocity 
increases, this thermal cause decreases; for at a velocity of 160 feet per second the 
thermal effect is such as would be due to the influence of stopped air alone. 
In prosecuting still further this part of our subject we made the following arrange- 
ment. A disc of mill-board, 32 inches in diameter, was fixed to the end of the axis of 
the whirling apparatus. An ether thermometer, whose bulb was one-fourth of an inch 
in diameter, was tied by its stem to the face of the disc, so that the bulb was 15 inches 
distant from the axis of revolution, and 1 inch from the margin of the disc. In the 
following Table the first five experiments were made with the above arrangement, but 
in the last two a thermo-electric junction of thin copper and iron wires, tied closely to 
the mill-board, was substituted for the ether thermometer. 
Seeies XIII. 
Velocities in the 
alternate experiments, 
in feet per second. 
Difference 
of thermal 
effect. 
Estimated 
effect of low 
velocity. 
Thermal 
effect of high 
velocity. 
Velocity due to 1° C., 
or V JO, on the hypothesis 
that V,o= -A. 
0 
0 
0 
3*1 0 *5 
0-029 
0-005 
0-034 
17-1 i 
7-85 and 3-1.5 
0-027 
0-034 
0-061 
31-7 
15-7 and 7*85 
0-032 
0-061 
0-113 
46-6 
31-4 and 15*7 
0-022 
0-113 
0-135 
85-5 
Thermo- '| gg.g 37-4 
electric 
junction J 
0-106 
0-120 
0-226 
133-3 
0-286 
0-116 
0-402 
142-3 
The surface of the mill-board disc being rather rough, it was judged desirable to 
make similar experiments with a disc of sheet zinc. This was perfectly smooth, 
36^ inches in diameter. The thermometer bulb was fixed at 17T inches distance from 
the axis. 
Series XIV. 
Velocities in the 
alternate experiraentsi 
in feet per second. 
Difference 
of thermal 
effect. 
Estimated 
effect of low 
velocity. 
Thermal 
effect of high 
velocity. 
Velocity due to 1° C., 
or Vjo, on the hypothesis 
that Vio= -A. 
' •Jt 
1-71 and -57 
0-024 
0-010 
0-034 
9-2 
.3-42 and 1-71 
0-017 
0-034 
0-051 
13-1 
8-55 and 3-42 
0-027 
0-051 
0-078 
30-7 
17-1 and 8-55 
0-023 
0-078 
O-IOI 
53-8 
34-2 and I 7 -] 
0-046 
0-102 
0-148 
88-8 
57-28 and 17-1 
0-070 
0-102 
0-172 
138-3 
The last columns of the two foregoing Tables clearly show the inapplicability of the 
law of the increase of temperature with the square of the velocity, at low velocities. The 
thermal effect appears even to increase at a slower rate than simply with the velocity. 
This phenomenon may, we think, be ascribed to the internal fluid friction of the particles 
