8 NATURE AND LIFE. 
they are not relative to the individuality of each atom, 
but to that of the whole which they form by being grouped 
together. Neither is it any caloric property, or optic, or 
electric, or magnetic one, because these properties result 
from the movements of the ether, within the more or less 
complex aggregate of the respective atoms of these two — 
substances. Now, if these atoms, taken separately, differ 
from each other in virtue of none of the properties just 
enumerated, they can only be dissimilar as regards two 
attributes, dimension and weight ; but difference in weight 
results from difference in dimension, and is not a quali- 
tative difference, but simply a quantitative one.* Con- 
sequently, any two heterogeneous atoms whatever, com- 
pared together, as atoms, have scarcely any of the differ- 
ential attributes peculiar to the groups which they make 
up by aggregation, and represent no more than two dis- 
tinct functions, two different values of one and the same 
initial matter, of one and the same primitive quality or 
energy. This simple demonstration establishes the unity 
of substance, not as a more or less plausible physical 
hypothesis, but as a metaphysical certainty, alike underiv- 
able and necessary. If we add now, reserving the demon- 
stration for a later period, that dimension, corporeal ex- 
tension itself, as Leibnitz said and as Magy has lately 
proved, is only a resultant of force, it will become evident 
that matter, in the last analysis, is reduced to force. 
Tyndall, in his biography of Faraday, tells us that one 
of the favorite experiments of this physicist gives a true 
image of what he was: “ He loved to show how water, in 
erystallizing, eliminates all foreign substances, however 
intimately mingled they may be with it. Separated from 
all these impurities, the crystal becomes clear and limpid.” 
1 We purposely take no notice of chemical forces, which can only be 
regarded as attractions, and must therefore be explained by forces acting 
outside of the atom itself. 
