i879-] 
The Course of Nature. 
81 
so simple that it is impossible to analyse them farther. 
Let us take as an instance of this the laws of the celestial 
motions. When Kepler discovered that the planets moved 
round the sun in eclipses, having the sun in one focus, he 
found what were, for his time, simple and elementary laws. 
They were entirely comprehensible, admitting of being 
expressed in mathematical language. They enabled him 
to predidf the motions of the planets, and, so far as the 
intellect of the time could penetrate, they could not be 
resolved into more simple expressions. 
But when Newton appeared on the scene, he showed that 
these and other laws could be expressed in the simple and 
comprehensive form of gravitation of every particle of matter 
toward every other particle with a force inversely as the 
square of the distance which separates them. All the laws 
of planetary motion which had before them discovered, 
were shown to be reducible to this one simple law, combined 
with certain fadts respecting the directions and velocities of 
the planetary motions. The most essential of these faCts is 
that the velocities of the planets in their orbits are such that 
under the influence of the sun’s gravitation, these orbits are 
nearly circular. 
By this grand generalisation Newton reduced the laws of 
the celestial motions to a form so elementary, simple, and 
comprehensive, that no further reduction seems possible in 
our state of knowledge. Attempts have been made to show 
that gravitation is itself the result of discoverable causes, 
but they appear to me entirely unphilosophical, since the 
causes into which they would resolve gravitation are more 
complex than gravitation itself. But for our present purpose 
it is not necessary to concern ourselves whether gravitation 
may arise from some more subtile principle as yet undis- 
covered. The point which I wish you to grasp is the entire 
comprehensibility of the law as it now stands. There is 
no mystery surrounding it. When I say that any body left 
unsupported will fall toward the centre of the earth until it 
meets with the earth itself, or some other obstacle to its 
farther fall, you know exactly what I mean, and what are 
the results of the law which I enunciate. In a certain sense 
we might say that the laws of nature are simply general 
faCts, distinguished from special faCts by their dependence 
upon certain antecedent conditions. Considered as such, 
there can never be any doubt as to their meaning or results. 
There is no profound philosophy involved in their adtion or 
expression any more than there is in such statements as that 
all unsupported bodies fall toward the centre of the 
VOL. vm. (n.s.) g 
