296 Astronomical and Nautical Collections. 
But in fact the force counteracting the solar and lunar attraction 
is by no means to be confounded with the operation of a support of 
any kind, attached to the solid parts of the sphere alone; for the 
force actually concerned in this case is equally efficacious with 
respect to the fluid parts; and, acting exactly alike on every par- 
ticle of the earth and sea, it precisely counterbalances the mean 
force of attraction, and leaves only the difference of the attractive 
powers, which are different for the different parts of the earth and 
sea, to exhibit its effects in disturbing the relative situations of 
those parts. This counterbalancing power is well known under the 
name of the centrifugal force, being derived from the velocity of 
the earth, either in its annual revolution round the sun, or, in the 
case of the moon, from its velocity in revolving round the common 
centre of inertia of the earth and moon. Since the earth actually 
falls at every instant as much within the tangent of its annual orbit, 
or the temporary line of direction of its motion, as it would de- 
scend towards the sun in an equal time, if it were otherwise at 
rest, this change of relation of the revolving body, which prevents 
its actual approach to the centre of attraction, and counteracts the 
force of gravitation, is, not improperly, considered as constituting 
a distinct force, and is characterized by the term centrifugal. Be- 
fore the introduction of the Newtonian theory, an attempt was 
made, by the celebrated Dr. Wallis, to deduce the tides from a 
difference of the centrifugal forces affectiug the opposite parts of 
the earth and sea, in revolving round the sun, and round the com- 
mon centre of gravity of the earth and moon; and Mr. Ferguson, 
in later times, has endeavoured to explain an opinion of a similar 
nature, by means of the whirling table; but the apparatus of Fer- 
guson was so constructed, as to produce a greater velocity of rota- 
tion in the remoter than in the nearer parts of the revolving system 
of bodies, which is a difference that does not exist in the case to 
be investigated; for the velocity of the different parts of the earth 
and sea, with respect to their common annual revolution round the 
sun, is precisely the same, the diurnal rotation being altogether in- 
dependent of this revolution, and producing modifications of force, 
which have their separate compensations, as distinctly indeed as 
