Dolbear.] 
184 
T Jan. 21, 
and Joule in 1843 discovered their quantitive relation approxi- 
mately and afterwards more exactly. Faraday about 1834 had 
shown the quantitive relationship between electricity and chemi- 
cal affinity, and Joule went over the ground of all the known 
forms of physical energy and proved not only their correlation 
but their conservation. 
The philosophical value of this work was not only the quantita- 
tive relation which was established, but it also made clear the 
idea that one might be the antecedent of another, and this was 
a new idea. It is true that one of the maxims of the old philoso- 
phy was “every effect must have a cause”; but that explained 
nothing. If this be transformed so as to be more precise and in 
accordance with what we call the Conservation of Energy it 
might read thus, every phenomenon must have a physical antece- 
dent, and as all phenomena involve energy, successive phenomena 
imply exchange of energy. Now energy is a product of two fac- 
tors, a mass and motion. A mass at rest possesses no energy. 1 
If, then, a mass of matter exhibits successive phenomena without 
any change in the mass quantity, or additional energy from with- 
out, the energy must be represented by a change in the character 
of the motion involved. Thus when a bullet with a velocity of 
1000 feet per second strikes a target it becomes heated ; the motion 
of translation as a whole has now been changed to individual 
molecular motions. If the whole of the energy of the moving 
bullet still remained in it after impact, the sum of the individual 
motions would be equal to the translatory movement, i. e. 1000 
feet per second. 
If the amount of matter in the universe is a constant quantity 
then the doctrine of the conservation of energy requires the 
amount of motion to be constant. It is not unfrequently said 
now-a-days, that matter and energy are the two factors in physical 
phenomena but the above considerations show that motion should 
be substituted for energy. A year or two before his death Max- 
well wrote a little treatise on Natural Philosophy which he named 
“ Matter and Motion ,” which shows that the above was his con- 
ception of the factors in physical phenomena. 
1 “ It is impossible to conceive of a truly dormant form of energy whose magnitude 
should depend in any way on the unit of time; and we are therefore forced to the con- 
clusion that potential energy, like kinetic energy depends upon motion.” P. G. Tait 
Art. Mechanics, Enc. Brit. § 297. 
