3 <5 2 ASTRO 
caufe any body expofed to forces, which tend to one com¬ 
mon centre, as is the cafe with the Earth, would necerta- 
rily aftitme a round figure. The aftent, however, of the 
modern philofopher to this truth, was not determined by 
fpeculative rcafoning; but on evidence, derived from faffs 
and actual obfervation. It is known, from the laws of op¬ 
tics and perfpective, that if any body, in all fituations, and 
tinder all circumftances, projett a circular (hadow, that 
body muff be a globe. It is alfo known, that eclipfes of 
the Moon are eaufed by the (hadow of the Earth. And 
tve find, that whether the (hadow be projected towards the 
eaff or the weft, the north or the fouth, under every 
circumffance it is circular: the body, therefore, that caffs 
the fhadow, which is the Earth, muff be of a globular fi¬ 
gure. We fiiall obtain another convincing proof of the 
globular fiiape of the Earth, by inquiring in what manner 
a perfon (landing upon the coalt of the fea, and waiting 
for a vert'd which he knows is to arrive, fees that veil'd. 
We fiiall find, that he firlt of all, and at the greateff dis¬ 
tance, fees the top of the maft riling out of the water; 
and the appearance is, as if the fhip was fwallowed up in 
the water. As he continues to oblerve the object, more 
and more of the inaff appears; at length he begins to fee 
the top of the deck, and by degrees the whole body of the 
-•veil'd. On the other li3nd, if the fhip be departing from 
us, we firfl lofe fight of the hull, at a greater difiance the 
main-fails dilappear, at a fiill greater the top-fail. But, 
if the furface of the fea were a plane, the body of the fhip, 
being the larged part of it, would be feen fit ft, and from 
the greatefl difiance, and the marts would not be vilible 
till i»,came nearer. 
Thefe faffs are clearly illufirated in the annexed figure ; 
but to render this, if polfible, (fill dearer, let us conlider 
two (hips meeting at fea, the top-maft of each are the parts 
firft difeovered by both, the hull, &c. being concealed by 
the convexity of the globe which rifes between them. The 
fhips may, in this inftance, be refembled to two men, who 
approach each other on the oppofite fides of a hill; their 
heads will be firft feen, and gradually, as they approach, 
the body will come entirely in view. From hence is deri¬ 
ved a rational method of eftimating the diftance of a fhip, 
w hich is in ufe amongft fea-faring people, namely, of ob¬ 
serving ‘ how low they can bring her down,’ that is to fay, 
the man at the maft-head fixes his eyes on the vert'd in 
fight, and (lowly defeends by the fhrouds, till !he becomes 
no longer vilible. The lefsthe difiance, the lower he may 
defeend before Ihe difappears. If obfervations of this 
kind be made with a telefcope, the effect is (fill more re¬ 
markable ; as the diftance increafes or diminifhes, the fhip 
in fight will appear to become more and more immerfed, or 
to rife gradually out of the water. This truth is fully 
N O M Y. 
evinced by the following confederation : that fhips have 
failed round the Earth, have gone out to the wefhvard, 
and have come home from the eaftward ; or, in other words, 
the (hips have kept the fame courfe, and yet returned from 
the oppofite fide into the harbour whence they firft failed. 
Now w e are certain that this could not be the cafe, if the 
Earth were a plane ; for then a perfon, who fitould fet out 
from arty one point, and go on ftraight forward, without 
flopping, would be continually going farther from the. 
point from whence he fet out. 
This argument is fully confirmed by the Earth having 
beenoften failed round : the.firft time was inthe year 1519^ 
when Ferd. Magellan made the tour of the whole globe 
in 1124 days. In the year 1557 Francis Drake performed 
the fame in 1056 days: in the year 1586 Sir Thomas Ca-. 
vendilh made the fame voyage in 777 days ; Simon Cordes, 
of Rotterdam, in the year 1590; in the year 1598, Oliver 
Noort, a Hollander, in 1077 days; Van Schouten, in the 
year 1615, in 749 days; Jac. Heremites and J0J1. Huygens, 
in the year 1623, in 802 days: and many others have fines 
performed the lame navigation, particularly Anfon, Bou¬ 
gainville, and Cook; fometimes failing round by the eaft- 
ward, fometimes to the weftward, till at length they arri¬ 
ved again in Europe, from whence they fet out; and, in 
in the courfe of their voyage, obferved that all the phe¬ 
nomena, both of the heavens and Earth, correfpond to- 
and evince, this fpherical figure, which is made more obi 
vious by the riling and fetting of the Sun, Moon, and 
ftars; all which happen fooner to thofe who live to the 
eaft, and later to thofe who liveweftwardly; and the mors 
or lefs fo, according to the diftance and roundnefs of the 
Earth. So alfo, going or failing to the northward, the 
north pole and northern ftars become more elevated, and 
the fouth pole and fouthern ftars more deprerted ; the ele¬ 
vation northerly increaling equally with the deprertion 
foutherly, and either of then* in proportion to the diftance 
gene. The fame thing uniformly happens in going foutlv 
ward. Beiides, the oblique afeenfions, defeenfions, amer- 
fions, and amplitudes, of the riling and fettingof the Sun 
and ftars in every latitude, are agreeable to the fuppofition 
of the Earth’s being of a fpherical form: all which could 
not happen if it was of any other figure. This globular 
figure may alfo be inferred from the operation of levelling, 
or the art of conveying water from one place to another; 
for, in this procefs, it is found necertary to make an allow¬ 
ance between the true and apparent level; or, in other 
words, for the fpherical figure of the Earth. For the 
true level is not a ftraight line, but a curve which falls be¬ 
low the ftraight line about eight inches in a mile, four 
times eight in two miles, nine times eight in three miles, 
fixteen times eight in four miles, ajways increaling in ex- 
aft ratio to the fquares of the diftance. The natural caufe 
of this fphericity of the globe is, according to Sir Jfaac 
Newton, the great principle of attraftion, which the Crea¬ 
tor has (lamped on all the matter of the univerfe; and by 
which all bodies, and all the parts of bodies, mutually 
attraff one another. And the fame is the caufe of the 
fphericity of the drops of rain, quickfilver, See. 
What the Earth lofes of its fphericity by mountains and 
valleys, is nothing confiderable; the higheft eminence be¬ 
ing fcarcely equivalent to the minuteft protuberance on 
the furface of an orange. Its difference from a perfect 
fphere however is more confiderable in another refpeft, 
by which it approaches nearly to the flatted form of an 
orange, or to an oblate fpheroid, being a little flatted at 
the poles, and raifad about the equatorial parts, lb that 
the axis from pole to pole is lefs than the equatorial dia¬ 
meter. What gave the firft occafkm to the difeovery of= 
this figure of the Earth, was the obfervations of fome 
French and Englifh philofophers in the Eaft Indies, and 
other parts, who found that pendulums, the nearer they 
came to the equator, performed their vibrations flower: 
from whence it follows, that the velocity of the defeent 
of bodies by gravity, is lefs in the countries near to the 
equator; and confequen.Uy tlfat thofe parts are farther re¬ 
moved 
