380 The Source of Electric Energy, fjuly, 
answer. In homogeneous bodies the tension of the mole- 
cules is similar, and their heat vibrations are, therefore, 
synchronous. The particles swing in exadt unison between 
the attractions to which their vibration is due. They do not 
come into contact with each other, nor do they in any way 
disturb each other’s condition of aggregation. They yield 
motive energy to one another only by the slow pull of 
attractive force. In homogeneous gases, however, the 
attraction is not sufficient to produce vibration. The mole- 
cules, therefore, move independently, and come into inces- 
sant contact. But, for reasons to be yet given, they do not 
disturb each other’s condition of aggregation. The chief 
result of their impaCt upon each other is the equalisation of 
motive energy. 
In heterogeneous bodies this synchronism of vibration 
does not exist. There is a certain degree of discordance 
between the motions of adjacent molecules. As a con- 
sequence they come into contact with each other. But there 
is another consequence of heterogeneity which is far more 
important ; a disturbance of the conditions of motion and of 
aggregation, which the molecules of each surface produce in 
those of the other. This disturbance we know by the name 
of eleCtric induction. It is the most significant feature of 
eleCtric aCtion, and possibly contains among its phenomena 
the solution of the mystery of eleCtric transmission. Before 
considering it, however, there are other essential features of 
the transfer of energy to be taken into account. Among 
these are some special points of analogy between the pheno- 
mena of light and radiant heat and those of electricity. 
If we examine closely the aCtion of radiant vibrations on 
solid and liquid substances, we find other effects than those 
already mentioned of partial absorption and conversion into 
heat. There are special resistances, which differ in degree 
in different substances. The energy of motion concerned in 
radiant vibrations cannot cease to exist. It must force itself 
upon molecules as heat vibration, force itself through masses 
as radiant energy, return through the air as radiant energy, 
or be converted into some other mode of motion, such as 
chemism or mass motion. And to every one of these changes 
in condition there is a resistance, the result being in exaCt 
accordance with the balance of resistances. If there be 
sufficient accord between the radiant vibration and the mole- 
cular heat vibration, the radiant energy will be absorbed as 
heat. If they be discordant there is a vigorous resistance to 
absorption, and the energy continues radiant. Two other 
ordinary resistances remain, the one a resistance to trans- 
