ASTRONOMY. 
when a ship goes out to sea, we first lose 
sight of the hull or body of the vessel, see 
fig. 4; afterwards that of the rigging; and 
at last can discern only the top of the nrast, 
which is evidently owing to the convexity 
of the water, between the eye and the ob- 
ject; for otherwise the largest and nrost 
conspicuous part would be visible the 
longest. Another proof is taken from the 
shadow of the earth upon the face of the 
moon, during the time of a lunar eclipse ; 
for the moon, having no light but what it 
receives from the sun, and the earth being 
interposed between them, the moon must 
either wholly or in part become obscure. 
And since in every eclipse of this kind, 
which is not total, the obscure part always 
appears to be bounded by a circular line, 
the earth itself, for that reason, must be 
spherical ; it being evident that none but a 
spherical body can, in all situations, cast a 
circular shadow. 
It is not ascertained who was the first 
person that asserted the figure of the earth 
to be spherical, but the opinion is of very 
great antiquity. For when Babylon was 
taken by Alexander the Great, it was 
known that the philosophers in that city 
had been long in the habit of calculating 
eclipses, which they could n«t have accom- 
plished without a knowledge of the ti ne fi- 
gure of the earth. Thales, who flourished 
six centuries before the birth of Christ, pre- 
dicted, according to the testimony of Hero- 
dotus, an eclipse of the sun. Hence it 
should seem, that in those early clays, the 
globular figure of the earth had been by the 
learned investigated and credited. This 
being known, its magnitude would also soon 
be discovered : the solution of this appa- 
rently difficult problem engaged the atten- 
tion of many great men about the same pe- 
riod ; and though the measures which they 
have given are wide of the truth, and even 
very difcrent from one another, yet this 
may be imputed to the inaccuracy of their 
instruments, and the want of mathematical 
knowledge rather than to the impractica- 
bility in the thing itself. Without, how- 
ever, entering upon this subject, we may 
observe, that the universe in general, as 
well as the solar system in particular, are 
in some measure connected with the mo- 
tion of the globe that we inhabit. By the 
universe may be understood the whole 
frame of nature, to the utmost extent of the 
creation, and by the solar system is meant, 
that portion of it which comprehends the 
sun, planets, satellites, and comets. Of 
this system the sun is supposed to be in the 
centre, round which there are eleven pla- 
nets continually revolving. 
If we can form a notion of the manner 
in which the earth moves, we shall easily 
conceive the motions of all the rest of the 
planets, and by that means obtain a com- 
plete idea of the order and oeconomy of the 
whole system. And in order to this, no- 
thing more is necessary than to consider the 
common appearances of the heavens, which 
are constantly presented to our view, and 
attend to the consequences. For since it is 
well known that the sun and stars appear 
to move daily from east to west, and to re- 
turn nearly to the same places in the hea- 
vens again in twenty-four hours, it follows 
that they must really move, as they appear 
to do, or else that we ourselves must be 
moved, and attribute our motion to them : 
it being a self-evident principle, that if two 
things change their situation with respect 
to each other, one of them, at least, must 
have moved. But if this change be owing 
to the revolution of the stars, we must sup- 
pose them to be endowed with a motion so 
exceedingly swift, as to exceed all concep- 
tion ; since it is now known, by calcula- 
tions founded on the surest observations, 
that their distances from us are so immense, 
and the orbits they have to run round so 
prodigiously great, that the nearest of them 
would move at least one hundred thousand 
miles in a minute. Now as nature never 
does that in a complicated and laborious 
manner, which may be done in a more sim- 
ple and easy one, it is certainly more agree- 
able to reason, as well as to the power and 
wisdom of the Creator, that these effects 
should be produced by the motion of the 
earth ; especially as such a motion will best 
account for all the celestial appearances, 
and at the same time preserve that beauti- 
ful simplicity and harmony which is found 
to prevail in every other part of the cre- 
ation. And tiffs argument will appear still 
more forcible, if wo compare the vast bulk 
of the celestial bodies with the bulk of the 
earth. For it is now well known, that the 
sun is above a million of times larger than 
the earth ; and from the best modern obser- 
vations it appears, that many of the stars 
are at least equally large. It is much more 
probable, therefore, that the earth revolves 
round its axis, with an easy natural motion, 
once in twenty-four hours, than that those 
immense bodies should be carried from one 
place to another, with such incredible 
swiftness. Nor is it any objection to tiffs 
