MOUNTAIN. 
acting in a direction different from that exerted by the 
whole mafs of matter in the earth, and with a proportion- 
ably inferior degree of force. 
Though fir Ilaac Newton had long ago hinted at an 
experiment of this kind, and had remarked, that “ a 
mountain of an hemilpherical figure, three miles high and 
fix broad, would not, by its attraction, draw the plumb- 
line two minutes (i' iS") out of the perpendicular:” yet 
no attempt to afcertain this matter by aCtual experiment 
was mhde till about the year 17385 when the French aca¬ 
demicians, particularly Meffrs. Bouguer and Condamine, 
who were fent to Peru to meafure a degree under the 
equator, attempted to dilcover the attractive power of 
Chimborazo, in the province of Quito, at that time fup- 
poied to be the higheft mountain in the world. Accord¬ 
ing to their obfervations, which were however made un¬ 
der circumftances by no means favourable to an accurate 
folntion of fo nice and difficult a problem, the moun¬ 
tain Chimborazo exerted an attraction equal to eight 
feconds. Though this experiment was not perhaps fuf- 
fieient to prove fatisfaCtorily even the reality of an at¬ 
traction, much iefs the preciie quantity of it; yet it does 
not appear that any ffeps had been fince taken to repeat 
it. Through the munificence of his Britannic majefty, 
the Royal Society were enabled to undertake the execu¬ 
tion of this delicate and important experiment; and the 
aftronomer royal was chofen to conduCt it. After various 
inquiries, the mountain Schehallien, fituated nearly in 
the centre of Scotland, was pitched upon as the molt 
proper for the purpofe that could be found in this illand. 
The obfervations were made by taking the meridian ze¬ 
nith dillances of different fixed liars, near the zenith, 
by means of a zenith-feClor of ten feet radius; firit on 
the fouth and afterwards on the north fide of the hill, 
the greatell length of which extended in an eaft and welt 
direction. It is evident, that, if the mafs of matter in 
the hill exerted any fenfible attraction, it would caufe 
the plumb-line of the feCtor, through which an obferver 
viewed a liar in the meridian, to deviate from its perpen¬ 
dicular fituation, and would attraCt it contrariwife at'the 
two Itations, thereby doubling the effeCt. On the fouth 
fide the plummet would be drawn to the northward, by 
the attractive power of the hill placed to the northward 
of it; and on the north fide, a contrary and equal de- 
fleCtion of the plumb-line would take place in confe- 
quence of the attraction of the hill now to the fouthward 
of it. The apparent zenith-diltances of the liars would 
be affeCted contrariwife; thofe being increafed at the one 
ftation which were diminilhed at the other : and the cor- 
refpondent quantities of the defleCtion of the plumb-line 
would give the obferver the fum of the contrary attrac¬ 
tions of the hill, aCting on the plummet at the two Ita¬ 
tions; the half of which will of courfe indicate the at¬ 
tractive power of the hill. 
The various operations requifite for this experiment 
lalted about four months; and from them it appears, that 
the fum of the two contrary attractions of the mountain 
Schehallien, in the two temporary obfervations which were 
fuccelfively fixed half way up the hill (where the effeCt 
of its attraction would be greatell), was equal to ir6". 
From a rough computation, founded on the known law 
of gravitation, and on an affumption that the denfity of 
the hill is equal to the mean denfity of the earth, it ap¬ 
pears that the attraction of the hill Ihould amount to 
about the double of this quantity. From thence it was 
inferred, that the denfity of the hill is only about half the 
mean denfity of the earth. It does not appear, however, 
that the mountain Schehallien has ever been a volcano, 
or is hollow; as it is extremely folid and denfe, and 
feemingly compofed of an entire rock. 
The inferences drawn from thefe experiments may be 
reduced to the following: 
1. It appears, that the mountain Schehallien exerts a 
fenfible attraction ; therefore, from the rules of philofo- 
/phizing, we are to conclude, that every mountain, and 
139 
indeed every particle of the earth, is endued with the 
fame property, in proportion to its quantity of matter. 
2. The law of the variation df this force, in the inverfe 
ratio of the fquares of the dillances, as laid down by fir 
Ilaac Newton, isalfo confirmed by this experiment. For, 
if the force of attraction of the hill had been only to 
that of the earth as the matter in the hill to that of 
the earth, and had not been greatly increafed by the 
near approach to its centre, the attraction thereof mult 
have been wholly infenlible. But now, by only fuppofing 
the mean denfity of the earth to be double to that of the 
hill, which feems very probable from other confiderations, 
the attraction of the hill will be reconciled to the general 
law of the variation of attraction in the inverfe duplicate 
ratio of the dillances, as deduced by fir Ilaac Newton from 
the comparifon of the motion of thejteavenly bodies with 
the force of gravity at the furface of the earth ; and the 
analogy of nature will be preferved. 
3. We may now, therefore, be allowed to admit this 
law, and to acknowledge that the mean denfity of the 
earth is at leall double of that at the furface; and confe- 
quently that the denfity of the internal parts of the earth 
is much greater than near the furface. Hence alfo, the 
whole quantity of matter in the earth will be at leall as 
great again as if it had been all compofed of matter of 
the fame denfity with that at the furface; or will be about 
four or five times as great as if it were all compofed of 
water. This conclulion, Mr. Malkelyne adds, is totally 
contrary to the hypothefis of lome naturalilts, “ who fup- 
pofe the earth to be only a great hollow lliell of matter; 
fupporting itfelf from the property of an arch, with art 
immenfe vacuity in the midlt of it.” But, were that the 
cafe, the attraction of mountains, and even fmaller ine¬ 
qualities in the earth’s furface, would be very great, con¬ 
trary to experiment, and would affeCt the meafures of 
the degrees of the meridian much more than we find they, 
do ; and the variation of gravity, in different latitudes, 
in going from the equator to the poles, as found by pen¬ 
dulums, would not be near fo regular as it has been 
found by experiment to be. 
4. As mountains are by thefe experiments found capa¬ 
ble of producing fenfible defleCtions of the plumb-lines 
of altronomical inltruments ; it becomes a matter of great 
importance, in the menfuration of degrees in the meri¬ 
dian, either to choofe places where the irregular attraction 
of the elevated parts may be fmall; or where, by their 
fituation, they may compenfate or counteract the effeCts 
of each other. 
The reader will bear in mind the arguments we have 
admitted, under the article Motion, (p. m.) in contra¬ 
vention of this doCtrine ; and may now decide for himfelf. 
DireBion of Mountains .—Buffon erroneoully believed 
that the molt elevated chains of mountains are the molt 
approximated to the equator. Mount Elias, which, un¬ 
der fixty degrees twenty-one minutes of north latitude, 
rifes to 12672 feet; Fair-weather Peak, fituated on the 
fame coalt, at fifty-nine degrees of latitude, which reaches 
to an elevation of 10240 feet; and, in fiiort, our European 
Alps; contradict this affection. If the loftieft fummits 
of the Old World are in the mountains of Thibet, and 
thofe of the New World in the centre of the Andes, near 
la Paz, we Ihould, on the contrary, infer that the higheft 
mountains are in the neighbourhood of the two tropics, 
and not of the equator; and that a chain of very high 
mountains may exill in the interior of Notafia, or New 
Holland, and in the fouth of Africa, fince the fouthem 
tropic traverfes thefe two continents. But we are not 
in poffeffion of a fufficient number of accurate obferva¬ 
tions to afcertain whether nature, in this relpeCt, has ob- 
ferved general and fixed rules; we only know that the 
mountain-chains which are fituated beyond the fifty-fifth 
degree of latitude, in each hemifphere, diminifh in height 
in proportion as we approach the poles; yet Mount Par- 
nalfus, in Spitzbergen, rifes to the height of 3666 feet, 
and Snteiials Jokull, in Iceland, to 4887 feet. 
Nature^., 
