Royal Astronomical Society. 307 
parison of their effects upon a pendulum: the nearness of the smaller 
mass making it produce a sensible effect as compared with that of 
the larger ; for by the known laws of attraction the whole earth must 
be considered as collected at its centre. 
Before giving any account of the different modes pursued, it 
may be permitted to pause a moment, and to consider the bearings 
of the result. Independently of the satisfaction which the mind 
receives from the conversion of relative into absolute knowledge, 
independently of the stimulus given to the advance of inquiry by 
the acquisition of such a resting point as the determination before 
us, and of the value which it adds to the theory of gravitation as an 
instructor of the world at large in the laws of nature, by enabling 
the teacher to present what would have been a mathematical con- 
ception in a more physical and tangible form—there are conse- 
quences of no mean importance which spring from the comparison 
of the whole earth with one of its definite parts. 
I do not undervalue considerations which present themselves at 
every step which is made, at every height which is scaled, when I 
confine myself on this occasion, and before this Society, to those 
only which particularly concern just knowledge of the foundations 
of astronomy, and fitting preparation for its advance among the 
physical sciences. 
When the Principia was published, one of the first who gave 
an unqualified adhesion to the general views of Newton was the 
justly celebrated Huyghens*. But there was one point which he 
could not bring himself to admit ; it was the universal attraction of 
every particle upon every other. He could not feel certain that 
because the attraction of the whole of one planet upon the whole of 
every other was established, it followed that the parts of each 
attracted the parts of all the rest and of each other. Newton did 
not, and could not, make this important conclusion a fundamental 
experimental fact, though he was able to advance almost an over- 
powering presumption in its favour: and it is easy to see how the 
student of Descartes, even when he had been brought to admit the 
attraction of planet upon planet, might have suspended his opinion 
as to the action of part upon part, until the cause of the pheno- 
menon, an inquiry much agitated in those days, was settled. But 
though the strong balance of probabilities in favour of Newton's 
opinion gradually gained for it a universal reception, there was no 
ocular and crucial evidence for the physical fact until the expe~ 
riments were made which I shall presently describe; and of those 
experiments, the one of Cavendish, which Mr. Baily has repeated, 
was by far the most convincing. Seeing is believing: and no one 
acquainted with the apparatus, and actually noting the visible 
effect of the approach of a leaden ball upon the oscillations of a 
torsion pendulum, after the nicest precautions had been taken to 
remove any possible effect of currents, magnetism, electricity and 
heat, could doubt the presence of a totally distinct agent, pro- 
* Hugenii Opera Reliqua, vol. i. p. 116. 
X 2 
