394 FRAGMENTS OF SCIENCE. 
This idea of distance between the attracting atoms is of 
the highest importance in onr conception of the system of 
the world. For the matter of the world may be classified 
under two distinct heads: atoms and molecules which have 
already combined and thus satisfied their mutual attrac- 
tions, and atoms and molecules which have not yet com- 
bined, and whose mutual attractions are, therefore, un- 
satisfied. Now, as regards motive power, we are entirely 
dependent on atoms and molecules of the latter kind. 
Their attractions can produce motion, because sufficient 
distance intervenes between the attracting atoms, and it is 
this atomic motion that we utilize in our machines. Thus 
we can get power out of oxygen and hydrogen by the act 
of their union; but once they are combined, and once the 
vibratory motion consequent on their combinations has 
been expended, no further power can be got out of their 
mutual attraction. As dynamic agents they are dead. 
The materials of the earth's crust consist for the most part 
of substances whose atoms have already closed in chemical 
union whose mutual attractions are satisfied. Granite, 
for instance, is a widely diffused substance; but granite 
consists, in great part, of silicon, oxygen, potassium, cal- 
cium, and aluminum, whose atoms united long ago, and 
are therefore dead. Limestone is composed of carbon, 
oxygen, and a metal called calcium, the atoms of which 
have already closed in chemical union, and are therefore 
finally at rest. In this way we might go over nearly the 
whole of the materials of the earth's crust, and satisfy our- 
selves that though they were sources of power in ages past, 
and long before any creature appeared on the earth capable 
of turning their power to account, they are sources of power 
no longer. And here we might halt for a moment to 
remark on that tendency, so prevalent in the world, to 
regard everything as made for human use. Those who 
entertain this notion, hold, I think, an overweening opin- 
ion of their own importance in the system of nature. 
Flowers bloomed before men saw them, and the quantity 
of power wasted before man could utilize it is all but infi- 
nite compared with what now remains. We are truly heirs 
of all the ages; but as honest men it behooves us to learn 
the extent of our inheritance, and as brave ones not to 
whimper if it should prove less than we had supposed. 
The healthy attitude of mind with reference to this sub- 
