8 
pretended that Newton either did state, or, considering the 
deficiencies of mathematical and physical knowledge in his day, 
could have stated, the axioms of natural philosophy in exactly 
the foregoing terms ; but the views propounded in the portions 
of the Principia referred to, and especially what he has asserted, 
in the Third Rule of Philosophizing, to be “ the foundation of 
all philosophy / ’ are in perfect accordance with the three kinds 
of hypotheses above defined, and, I may say, have to a great 
extent suggested them. 
11. Before proceeding to inquire by what arguments the 
truth of these hypotheses may be established, it must first be 
settled that they conform to the two regulative conditions 
stated in sec. 9, according to which they must be perfectly 
intelligible from sensation and experience, and must not involve 
any assertion expressive of variation or degree. With respect 
to the first hypothesis, since we know by common experience 
that masses can be broken up into parts, and these parts into 
smaller parts, and so on, it is quite conceivable that all bodies 
may be composed of very minute parts, and it is not inconceiv- 
able that there may be a limit to the divisibility into parts. 
Thus to say that matter is composed of atoms properly so called, 
is an intelligible assertion, apart from and prior to any evidence 
that such is its composition. And the further assertion that 
matter is composed of discrete atoms, that is, atoms with inter- 
vening spaces, is alike intelligible. 
12. Again, when it is said of an atom, that it is a very small 
inert sphere of invariable magnitude, there is nothing in this 
definition which is not perfectly intelligible from sensation and 
experience ; for from sensation we can perceive what inertia is 
in masses, and thence infer what it is in their component parts 
(see sec. 15 of “Metaphysics of Scripture”), and by the senses 
of sight and touch we can understand what is signified when an 
atom is said to be a sphere of invariable magnitude. Thus the 
atom, as above defined, is conformable to both the regulative 
principles laid down in sec. 9. 
13. With respect to the third hypothesis, the definitions of 
the ether and of the mode of its pressure on the atoms involve 
no postulates that are not perfectly intelligible from what we 
know by experience of the dynamical properties of air of given 
temperature. And as to the quality of pressure, it suffices in 
this philosophy to appeal to the fact that wo feel what it is 
when we press with the hand against any solid substance. 
(More will be said on this point in a subsequent part of the 
essay.) It might, however, be urged that inasmuch as the 
third hypothesis assumes that the pressure of the ether is 
always and everywhere proportional to its atomic density, it 
