836 
PROFESSOR 0. REYNOLDS ON CERTAIN DIMENSIONAL 
and when - is large 
It thus appears that the present results entirely confirm the previous results so far 
as they went; and the present investigation is a completion, not a correction, of the 
former one. 
The present investigation shows that, besides being proportional to the quantity of 
heat, the force is proportional to the linear divergence of the lines along which the 
heat flows ; and hence, if these lines are parallel, no matter how great may be the 
difference of temperature, the gas can exert no pressure above the normal pressure 
which it will exert on all surfaces alike. This is the case, whether the heat is commu¬ 
nicated to gas or is spent in causing evaporation from the surface. 
The relation between the difference of pressure and the divergence of the lines of 
flow affords a clear explanation of the complex phenomena of the radiometer; and as 
these phenomena have attracted a great deal of interest, I feel that an explanation of 
them will not be out of place. 
Pc- 
/ 
-p = 
_ v / 77 H 
18" cV 
8 
1 s H 
-p 
“11 
\/ 7T C C 2 5£ 
Divergence of the lines of flow and the radiometer. 
120. We may readily obtain a graphic representation of the results expressed by 
equations (124) and (140). 
Fig. 12, 
Let A B, fig. 12, be a plate from which heat is being communicated to the surround¬ 
ing gas. Then the lines representing the flow of heat, drawn according to the law of 
conduction, are shown in the figure, 
(1.) The shape of these lines depends on the distribution of temperature over A B. 
