Gravitation are occasioned ly known Terrestrial Motion. 105 
generated i in each stratum, and the forces generating those mo- 
tions, are in the same ratio. On this point there is nothing to 
add or to alter. If the concentric strata were in density recipro- 
cally as the squares of their distances, and undisturbed, there 
would be no phenomena; but it is the disturbance of that which 
has been in a state of equilibrium (either by distance frem the 
centre, or by the resistance of friction), which occasions the 
sensible phenomena of weight, or of falling bodies. 
I do not, however, consider that these observations conclude 
the subject ; for [ admit, that all the circumstances which exist 
among the parts of a sphere, moving in an orbit, the momenta 
of whose masses in the concentric strata are equalized by a ro- 
tary motion, as well as the effects arising from the centre of 
density, not being the mathematical centres and also from ac- 
cidental disturbances in the equilibrium of particular bodies, 
merit the careful analysis of philosopical mathematicians. 
At the same time, although the mathematical laws must ne- 
cessarily be the same, it is not indifferent, in human inquiries, 
whether physical phenomena are ascribed generally to gravita- 
tion, of which nothing is affected to be known, or to motion, of 
which we may not know the primary origin. We know, at any 
rate, more of motion than we know of gravitation. Besides the 
laws common to both, we know that motion is an accident of 
bodies which gives them momenta, and causes them to change 
their situations in space; and we know that some motions are 
general, antecedent, or primary, and that others are local, con- 
sequent, or subordinate. 1n the problem before us, we are there- 
fore enabled to show that known effects are conseguences of se- 
veral known motions, thereby attaining a degree of analysis, which 
could never be effected, if we referred the same phenomena to 
the general name of gravitation. 
Conclusion. These, I believe, are the chief objections which 
have been imagined and promulgated in opposition to a theory 
which substitutes the known motions of Nature as operative 
causes of certain physical phenomena, in place of an assumed 
principle called gravitation, by which, false analogies have been 
introduced into philosophy, and effects ascribed to a cause neither 
proximate nor in contact. It may be difficult to analyse, in like 
manner, the motions which produce al! the celestial phenomena, 
or trace the sources of particular motions; and it may be im- 
possivie for rian to ascertain aty other origin of motion than the 
sublime cats oy Vases: bot we advance another step in hu- 
man knowledge when we discover that the two-fold motions of 
a planet are competent to the consolidation and unity of its 
mass, and are eflicient causes, by means of which bodies removed 
out of their equilibrium are restored to the mass. 
XIV, On 
