110 On the Measure of 
It is true they have not been usually’ stated 
in the same terms: but I believe the same 
inferences strictly follow from the reasoning of 
many other good writers on this subject. If 
forces be mathematical quantities, we may 
reasonably enquire how it is that they are so 
indeterminate in relative magnitude ? 
If two given lines, angles, surfaces, or 
solids be equal, they are equal in whatever 
manner they may be applied, or however they 
may be measured. But if we have two given 
bodies, moving with velocities inversely as their 
masses, their forces, it would appear, are 
either equal or unequal, according as they 
may be classed under one or other of the 
above subdivisions of mechanical phenomena. 
If the forces of two given bodies in motion 
are either equal or unequal, according to the 
purpose ‘to which they may be applied, it 
would’ be very desirable to have a complete 
and accurate classification of all the pheno- 
mena of force, exhibiting the variations to 
which they may be subject ; and we are so far 
indebted to Mr. Atwood, that he is, I believe, 
the only author who has attempted to make 
such anarrangement. But his arrangement is 
not complete, for he has omitted to include 
in it many important practical applications of 
force ; such, for example, as the raising of a 
