ASTRONOMY. 
219 
the land would have Deen covered: had there been much 
less than there is, there would not have been enough to 
fertilize the continent.* Had the exsiccation been pro¬ 
gressive, such as we may suppose to have been produced 
by an evaporating heat, how came it to stop at the point at 
which we see it? Why did it not stop sooner; why at all? 
The mandate of the Deity will account for this; nothing 
else will. 
IV. Of centripetal forces. By virtue of the simplest 
law that can be imagined, viz. that a body continues in 
the state in which it is, whether of motion or rest; and if in 
motion, goes on in the line in which it was proceeding, 
and with the same velocity, unless there be some cause for 
change: by virtue, I say, of this law, it comes to pass 
(what may appear to be a strange consequence) that cases 
arise, in which attraction, incessantly drawing a body to¬ 
wards a centre, never brings, nor ever will bring, the body 
to that centre, but keep it in eternal circulation round it. 
If it were possible to fire off a cannon ball with a velocity 
of five miles in a second, and the resistance of the air could 
be taken away, the cannon ball would forever wheel round 
the earth, instead of falling down upon it.f This is the 
principle which sustains the heavenly motions. The Deity, 
having appointed this law to matter, (than which, as we 
have said before, no law could be more simple,) has turned 
it to a wonderful account in constructing planetary systems. 
The actuating cause in these systems, is an attraction, 
which varies reciprocally as the square of the distance; 
that is, at double the distance, has a quarter of the force; 
at half the distance four times the strength; and so on. 
Now, concerning this law of variation, we have three 
things to observe: First; that attraction, for anything we 
know about it, was just as capable of one law of variation 
* Nearly three quarters of the earth’s surface are covered by the sea. 
Now evaporation is proportionate to the surface of the fluid, and conse¬ 
quently a less expanse of waters would not have afforded a sufficient sup¬ 
ply of rain, whieh does not now fall upon the whole, in greater quantities 
than are required “ to fertilize the earth.”— Paxton. 
t If a body be projected horizontally from a station A, Fig. 6, Plate 
XXXIX, which is at a certain height, its weight or the force of gravity 
will draw it towards the earth. It may be supposed to come down, 
for example, at B. But from the tendency which the body has to con¬ 
tinue in the state of motion which is communicated to it, it will be carri¬ 
ed farther before it falls, if it is projected with a greater force. Hence, 
if this force be increased it may be made to reach C; by a greater increase, 
it may be carried to D; or even round to A, from whence it originally 
»et out.— Ibid. 
