102 PROCEEDINGS OF SECTION A. 
“law,” and this was supplied a few years later by Hooke 
himself. So it has sometimes been thought that Hooke 
ought to share the honours of the law of gravitation with 
Newton. However, it is 1mportant to bear in mind that 
Hooke did not fulfil his promise to prove that his laws could 
be applied to the motions of the planets; and this makes all 
the difference between success and failure. To occupy one 
self with speculations about gravity after the manner of 
Hooke is largely a waste of time and energy. It serves no 
useful purpose. To prove, as Newton did, that a law may 
be laid down which strings together all our knowledge of the 
planetary motions, is rightly accounted one of the greatest 
achievements of the intellect. The one thing that makes 
the “law” of gravity worth discussing at all is that, as a 
matter of fact, it does “‘ explain’ the motion of the planets. 
Newton was the first to prove this, and so Newton rightly 
wears the crown of victory. Still. for all this, the law of 
gravity is no “‘explanation”’ in the sense of referring the 
unknown to the known. It is only an hypothesis. New- 
ton’s famous saying—'‘* Hypotheses non fingo’’—is often 
misunderstood. He is contemptuous of mere hypotheses— 
those that serve no useful purpose—but he does not mean 
to discourage altogether the making of hypotheses. He 
made a great many himself. It was a leap in the dark on 
Newton's part to go from the apple to the moon; a pure 
assumption to suppose that both were subject to the same 
“law.’’ But he was not afraid to try it as an hypothesis, 
and he was ultimately rewarded (as we know) by finding 
that it fitted in with the facts. And Newton’s Regula 
Philosophandi are really nothing more than suggestions for 
guidance in the framing of hypotheses:-—Rule I.: ‘‘ No 
more causes of natural things are to be admitted than are 
sufficient to explain the phenomena of these things.” This 
is merely a statement of convenience. For practical pur 
poses we want as few “laws” as possible. Rule IL: 
“Those qualities of bodies that can be neither increased nor 
diminished, and that are found to belong to all bodies within 
the reach of our experiments, are to be regarded as the 
universal qualities of all bodies. . . . If it universally 
appear, by experiments and astronomical observations, that 
all bodies in the vicinity of the earth are heavy with respect 
to the earth, and this in proportion to the quantity of 
matter that they severally contain; that the moon is heavy 
with respect to the earth in proportion of its mass, and our 
seas with respect to the moon; and all the planets with 
