Chapter I

The bases of modern astronomy. Their late formation 18
Instruments and measures used by ancient astronomers 19
Weights and measures sought out by modern astronomers 20
Means employed to discover the density of the earth.
Measuring by means of plummets not sufficiently exact 20
Measurements with torsion and chemical balances more accurate 21
Sir George B. Airy's theory,
and experiments at the Harton colliery 22
Results of experiments not reliable.
Theory contrary to the Law of Attraction 23
Proof by arithmetical calculation of its error 24
Difficulties in comparing beats of pendulums at top
and bottom of a mine 26
The theory upheld by text-books without proper examination 27
Of a particle of matter within the shell of a hollow sphere.
Not exempt from the law of Attraction 28
A particle so situated confronted with the law of the
inverse square ofdistance from an attracting body.
Remarks thereon 29
It is not true that the attraction of a spherical shell
is "zero" for a particle of matter within it 31