138 PROFESSOR O. REYNOLDS ON INCOMPRESSIBLE VISCOUS 
must depend on mechanical principles and the properties of matter, and hence the 
direct passage of energy of relative-mean-motion to energy of heat-motions is evidence 
of a general cause of the condition of actual-motion which results in transformation— 
which may be called the cause of transformation. 
The Discriminative Cause, and the Cause of Transformation. 
11. The only known characteristic of heat-motions, besides that of being relative 
to the mean-motion, already mentioned, is that the motions of matter which result 
from heat are an ultimate form of motion which does not alter so long as the mean- 
motion is uniform over the space, and so long as no change of state occurs in the 
matter. In respect of this characteristic, heat-motions are, so far as we know, 
unique, and it would appear that heat-motions are distinguished from the mean- 
motions by some ultimate properties of matter. 
It does not, however, follow that the cause of transformation, or even the 
discriminative cause, are determined by these properties. Whether this is so or not 
can only be ascertained by experience. If either or both these causes depend solely 
on properties of matter which only affect the heat-motions, then no similar ettect 
would result as between the variations of mean-mean-motion and relative-mean- 
motion, whatever might be the difference in magnitude of their respective periods. 
Whereas, if these causes depend on properties of matter which affect all modes of 
motion, distinctions in periods must exist between mean-mean-motion and relative- 
mean-motion, and transformation of energy take place from one to the other, as 
between the mean-motion and the heat-motions. 
The mean-mean-motion cannot, however, under any circumstances stand to the 
relative-mean-motion in the same relation as the mean-motion stands to the heat- 
motions, because the heat-motions cannot be absent, and in addition to any trans- 
formation from mean-mean-motion to relative-mean-motion, there are transformations 
both from mean- and relative-mean-motion to heat-motions, which transformation 
may have important effects on both the transformation of energy from mean- to 
relative-mean-motion, and on the discriminative cause of distinction in their periods. 
In spite of the confusing effect of the ever present heat-motions, it would, however, 
seem that evidence as to the character of the properties on which the cause of trans- 
formation and the discriminative cause depend should be forthcoming as the result of 
observing the mean- and relative-mean-motions of matter. 
12. To prove by experimental evidence that the effects of these properties of 
matter are confined to the heat-motions, would be to prove a negative; but if these 
properties are in any degree common to all modes of matter, then at first sight it 
must seem in the highest degree improbable that the effects of these causes on the 
mean- and relative-mean-motions would be obscure, and only to be observed by 
delicate tests. For properties which can cause distinctions between the mean- and 
