1891 - 92 .] Dr W. Peddie on Transformation of Energy. 255 
discussed fully later.] It is easy to see that equation (3) is in 
reality no less general than equation (2) ; for, before we could apply 
(2) to any particular case in which (say) energy of the type (A, a) is 
transformed into other types, we should have to break up the total 
quantity of energy of type (A, a) into its several parts, which are 
transformed, as far as possible, into the several types ; and we 
should then have to consider each part separately. That is to say, 
we should have to resolve equation (2) into a series of equations of 
the form (3). 
We may write (3) in the form 
dAda 
— d .dp , 
dA , , 
or ——.Ada 
A 
= d.dp , 
dA 
^.e., —rda 
A 
= d.dp, . . . . 
... (4) 
where da is the amount of energy of the type (A, a) which enters 
the system in the first operation of the cycle described above, and 
dj8 is the amount of the type (B, b) which is developed by trans- 
formation. The equation (4) expresses the principle of degradation, 
for it asserts that only the fraction dA/A of the whole amount of 
energy of the type (A, a) which is supplied is changed into energy 
of the type (B, 6). If aj^ be the whole amount of the type (A, a) 
which is supplied, while is the amount of that type which remains 
untransformed, we may write (4) in the form 
A]^ — Aq 
- «2 • 
This equation gives a definition of A on an absolute scale (which 
includes Kelvin’s definition of absolute temperature as a special 
case), for a generalisation of Carnot’s reasoning regarding the effi- 
ciency of a reversible heat-engine shows that the working of our 
more general reversible system is independent of the nature of the 
working-substance. It may be put in the form 
which applies to a completed reversible cycle, and includes, as a 
