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2. Taking advantage of the above-mentioned admission, Hume proposed, 
in place of a theory of causation, the hypothesis of mere antecedence and 
consequence according to invariable law. This idea, which has been very 
generally adopted by modern metaphysicians, is virtually an abandonment 
of the reality of intelligible causation, and gives a kind of omnipotence to 
law. The denial of the possibility of miracles is a logical consequence of 
accepting it ; and, in short, the same dogma forms the basis of all the sceptical 
and neological opinions that have in recent times prevailed so much in 
Germany and France, culminating, as it were, in the writings of Strauss and 
Renan. 
3. The natural philosophy of which Newton laid the foundation, and 
indicated the rules (in Book III. of the “Principia”), leads, when legiti- 
mately applied, to conclusions in direct contradiction to Hume’s principle of 
antecedence and consequence without assignable cause. Newton conceived 
that all the physical forces, inclusive of gravity, might be modes of action of 
a universal elastic medium (the aether ), the sensible existence of which is now 
generally recognized. Such a medium acts necessarily by pressure, and, 
therefore, in a manner comprehensible by us, because we know by personal 
sensation and experience what pressure is. In fact, on the hypothesis that 
the aether is so constituted that variations of its pressure are always and 
everywhere proportional to variations of its density, all the modes of its 
action are such as come within the province of calculation by mathematics. 
It is thus known, for instance, how light, which is one form of physical force, 
travels by means of the aether uniformly with an immense velocity through 
illimitable space. 
4. Besides the existence of the aether, the antecedents of physical science 
point to the fact that all visible and tangible substances are composed of 
indivisible parts, called atoms, to which, on the above view of the nature of 
the physical forces, there is no need to attribute any qualities other than 
inertia, and constancy of form and magnitude. The aether, the atoms, and 
the juxtaposition of atoms in definite arrangements and proportions so as 
to constitute the simpler natural bodies, being given, together with the 
intrinsic qualities of the aether and the atoms, all the elements for con- 
structing the material universe are furnished, as well as all the data required 
for submitting to calculation the various operations by which it has been 
brought into its present condition, and is maintained therein. In short, 
according to this philosophy, all quantitative relations admit of being ascer- 
tained by mathematical reasoning ; and the mere fact that the word 
“ square ” occurs in the enunciation of the law of gravity is evidence that 
the proof of the law is within the province of mathematical investigation. 
I am far from asserting that physical science has reached, or even approached, 
the completeness and comprehensiveness of which I have here supposed it 
to be capable ; it is sufficient for my present purpose to have ground for 
saying that arguments drawn from its actual condition afford a reasonable 
presumption that the above statement correctly describes its essential 
character.- (Such arguments will be found in my work on the “ Principles 
