576 DOLBEAR. [Vou. II. 
molecules, and ether, that the latter is affected by motions of 
the former because they spend their energy upon it in some 
cases, and in others receive energy from it. This is true for 
light, for magnetism and electricity, and these are explained as 
setting up undulations or special stresses in the ether. If one 
considers the space affected by a heat vibration of an atom as 
its field, it appears to be as large as the universe, for the undu- 
lation travels on in straight lines to an indefinite distance, as do 
sound vibrations in the air; but the maximum displacement or 
change in the density or stress in the medium must necessarily 
be greatest where the amplitude of motion is greatest ; namely, 
immediately adjacent to the vibrating body itself. Assume that 
the vibrating atom lessens the density of the ether adjacent to 
it, and at once it is seen that other atoms near by will be 
crowded towards the one thus vibrating —there is an apparent 
attraction within its field. But the heat vibrations of an atom, 
as represented in Fig. 1, will have a field somewhat like 
that of a tuning-fork ; for, as 
shown, there are four nodes 
: 5 \ where there would be no les- 
sening of the pressure, and 
four parts where such les- 
sening would be at its max- 
imum. Consider, then, two 
atoms adjacent to each other, 
but not in contact; and 
one of them vibrating in its 
fundamental rate, Fig. 3. 
The modés” are’ ata, 2304 
and 4; and if the spaces marked 5, 6, 7, and 8 represent the 
variable pressure spaces or the field of the atom, it is shown 
that the other atom will be in a space of less pressure at 6 than 
at 9, and consequently will be crowded towards 6, where the 
amplitude is greatest; but because it is greatest, it will be in 
unstable position, and will move to one or the other nodes, I or 
2, where it will be held while the vibration is kept up. If the 
second atom vibrates also, that will only double the strength 
of the field at 6 and make the pressure towards each other 
stronger than before, and the two will join nodes at I or 2. 
But there are four nodes, and consequently as many places 
