being a property of matter, vital force is but a property of 
rD jitter 
16. This is all clear and definite. Nothing is wanting but 
accuracy in the foundation facts, and logical sequence for the 
superstructure. 
17. To prove this, I must beg my audience to accompany 
me through a dissertation requiring some close attention. 
Atoms. 
18. In the first place, then, as to atoms and molecules. 
Ponderable matter is no doubt (in thought) infinitely divisible, 
but, in reality, this division has a limit beyond which the most 
powerful forces which we can bring to bear have no longer any 
effect. We therefore call these ultimate particles of matter 
atoms , from the Greek arogog (from a privative, and regvu), I 
cut), implying that which is incapable of any further division. 
19. Notwithstanding their excessive minuteness, we have 
succeeded in assigning some of their properties, such as deter- 
mining their relative weight. Of their form we are completely 
ignorant, but the probability is that they are spheroidal, and 
that each atom is a microcosm in the sense of having polarities 
and capacities of revolution on its axis, like the sphere of the 
earth. 
20. A certain property of these atoms has received the name 
of atomicity , t indicating their capacity for combination. We 
know that 1 atom of chlorine combines with 1 atom of hydrogen, 
1 atom of oxygen combines with 2 atoms of hydrogen, 1 atom 
of nitrogen combines with 3 atoms of hydrogen, 1 atom of 
carbon combines with 4 atoms of hydrogen. 
21. These simple bodies differ among themselves by their 
capacity of combination with hydrogen, this being measured 
by the number of atoms of that element which they are capable 
of fixing. 
22. A somewhat different property of atoms is their affinity ; 
the cause, whatever it may be, of chemical combination. When 
a mixture of oxygen and hydrogen has been exploded to form 
water, we say that affinity has united the two primitive gases 
into a homogeneous liquid. The affinity is measured by the 
quantity of force ( vis viva) which is transformed by the effect 
of combination, and which is manifested as heat. The energy 
with which a body combines with another body is looked upon 
* Protoplasm , p. 24. 
f I am not answerable for this term, to which exception may be taken, 
neither do I pledge myself to the exact accuracy of the definition. It seems 
provisionally necessary. 
