102 On the Doctrine that the Phenomena of Terrestrial 
IV. It is contended that the Galilean laws of falling bodies 
cannot be accounted for, except on the principle of a continually 
acting attraction. 
To this I reply, that the great terrestrial motions are, in like 
manner, continually acting ; and that from like causes they must 
produce like phenomena whenever any body is placed in cireum- 
stances to become the sensible patient of their activity. 
V. It is urged that local affections of mountains, or other 
“masses, can result only from the attractive influence of those 
masses; and the experiments of Maskelyne and Hutton, of 
Bouguer, of Zach, and of Cavendish, are adduced as proofs. 
A mighty host, if their acumen and their accuracy bore on 
the question! But, as I refer all phenomena to a centre of 
motion, and the Newtonians refer them to a centre of attraction, 
and as both centres are generated by the actual dispositions of all 
‘the masses of the aggregate—so both centres are varied in po- 
sition by unequal arrangements of the masses; and the motions 
on the surface referable to such centres are varied accordingly, 
and in equal degrees, upon both hypotheses. 
If the earth were an equal and homogeneous sphere, then all 
the phenomena of falling or suspended bodies would have re- 
ference to the mathematical centre of the mass, and the plumb- 
line would always hang perpendicularly to the visible horizon ; 
but, if a mountain, or any unequal mass, be placed on the sur- 
face, then on one hypothesis the centre of the motion, or on 
the other the centre of the attraction, will be raised above the 
mathematical centre, in a certain proportion, towards that 
mountain, creating a new physical centre; and all the deflec- 
tions of the rotary motion on this theory, or all the attractions 
on the Newtonian theory, will be made with reference to that 
new centre. The maximum of variation will take place nearest 
to the projecting mass ; and, if the mass were suddenly created, 
or brought near a suspended plummet, it would turn it aside, 
in a given proportion of the bulk of the mass to the bulk of 
the earth; and, as in Mr. Cavendish’s experiment, it might 
perhaps be possible to measure the impulse. But, in every 
possible case of such inequalities, the same phenomena must 
and would result from thus varying the centre of the aggregate ; 
whether the phenomena were ascribed, as now, to the efficient 
and operative motions of the earth, or, as heretofore, to the 
principle called by the name of attraction*, 4 
ff 
* T have taken it for granted that these experiments and calculations are 
correct, because the true results must be included in the laws of motion, as 
well as those of gravitation; but I remark, with profound deference to the 
learned calculators, that the Schihallien result assumes two-thirds of the 
circumference for theearth’s attraction as a quantity admitted 3 apt ise 
tT, 
