DENSITY. 
t= 3”.90554, hence . = 0.0883. Alfo P = 13.462 days, 
hence d = = 8.0149. 
Oz 0.0883? X 13.462? 
os denfity of — was computed, by Dr. Mafkelyne, 
to be 1.024. de la Lande makes it 1.038 
The denfities of the planets, determined by this. method, 
will be nearly as follow 
un 0.25226 
Mercury 2.58330 
Venus 3.02400 
Earth 1.00000 
Mars 0.65630 
ae 0.20093 
Satur 0349 
Georgian 0.21805 
Denfity of the Earth. 
In the above computations, the fun or the earth hath been 
affumed as the unity, from which the other denfities- have 
been computed. 
it is a queftion of no lefs intereft to know the denfity 
a a ftandar 
of com a n, when we confider the fpecific gravities of 
other 
Dr. Mafkelyne, the prefent caer ai royal, was the erie 
perfon that determined experimentally the denfity of th 
earth by meafuring the attractive oo of the mountain Sc. 
hallien, on the plumb-line of a zenith fe€tor. He interred 
certain, as it was requifite to have given the internal ftruc- 
ture of the mountain, which.could not be known but by 
-conjectur 
But i jate experiments of Mr, Cavendifh have left us 
very little uncertainty upon this fubje&; he ean see the 
-mean denlity of the earth to be 54 greater than w 
The experiment of Mr. Cave onde on the 
fame aad as that of Dr. Mafkelyre; the reader willfind 
a very e defcription of every part of the procels in 
io Philofophical ease cue for 1798, from which we 
roper to give a fhort explanation of the prin- 
-ciple on shit it is foun 
If a ball.a ( Plate 1X. ronan. Jig. 60.) be fufpended by 
-a thread in.the manner o dulum, and a large ball A, be 
.placed on one fide of it, ‘f lie pera of A be fenfible 
on the fmaller ball, it will be defleed from its vertical pofi- 
‘tion and will affume new one, as @, where it will remain in 
i t is demonftrated by the 
is to ius: therefore when w 
power ie ‘100 weight of lead, for inftance, at the diftance 
a, we can calculate how many hundred weight muft be 
placed at 40G0 miles diftance, or at the centre of the earth ; 
‘to retain the ball in equilibrio at 4, this weight is evidently 
that of the whole earth. Now to render the {mall arc aa 
fenfible, it is evident we muft either have a pendulum of 
an exceffive length, or the ball A of 
In Dr. Mafkelyne’s experiment the 
was chofen. The mountain Ae aie ait the ball 
spendulum was the plum f zenit 
former one is qaopeeiae ate f Mr. Cav 
a ingenul Pike of the mechani{m a ts in the fabititution 
rt horizontal pendulum, equal in fenfibility to a 
wee one of immenfe length: for we fhall find that the 
pendulum in the ee pe alana vibrated only four 
n hour: now a pendulum fufpe — vertically “to 
have vibrated equa ay is nd to have 
equally fenfible to the seis of the ball ‘A, 
been between four and five hundred miles in icae eh. 
The apparatus confifts of a flender horizontal arm, about 
fix feet long, having at its extremities two {mall leaden balls 
of two inches diameter ; this is fufpended by a fine wire 40 
wooden cafe to 
therefore 
ave 
draw the balls on one 
will affume a given, prfition, i in whic ey wi 
ranged wil vibrate, ae ne 
end on ae C inity of the 
Small pieces of ivory, eating divifions to the 2oth 
Hae of an inch are placed within the cafe; thofe in the 
direCtion a Ace d hl confidered as plus; thofe in the direc- 
tion ad, bu, 
“wo ate wee about 508 - oe are brought 
means of an apparatus without age into either of 
the pofitions or w w, or the a may be kept at right 
angles to the arm 7 which cafe they he no tendency to 
produce motion in the {mall balls a or 3. 
The object of the experiment is, next, to determine the 
time of the vibrations of the arm, and the angular deviation 
from its central pofition caufed by the attraétion of the 
leaden weights, The author, after defcribing the appa ratus, 
proceeds to give the mioute detail of se fets of experi« 
ments, of which the refults were as follows: . 
a ae x! we lw | ée 
z | Motion | ©&] § | 38/8 |Aze 
GS lee | Bo) 2) eS ee ee 
a. eight.} (o ¥ = Se ie | se 
4 | sa] A | RS | 4 lige 
F oto +] 14.32 | 13.42 5-5 
. 1 +too ] 14.1 | 13-17 | 14.95 5-61 
. { Oo to+ ] 15.87 | 14.69 4.88 
+ too] 15.45 | 14.14 | 14.42 107 
"fF +to of 15 22 | 13°56 | 14.39 326 
2 1 otot| 145 | 13.28 | 14.54 35 
oto+{] 3.1 2.95 6.54] 5-35 
4 { +to—{ 6.18 Fel 5-29 
—to+] 5.92 43 5.58 
5 { + to—| 5.9 7-5 5-65 
— to+ 5-98 4-5 
ON 3-05 | 29 4-53 
6 { —to+ 5-9 571 5-62 
¥ { Oo to—]| 3.15 | 3-03 4 5.29 
—to+ | 6.1 59 5:44 
8 f o to— | 3.13 | 3.00 Joy meani6.57] 5.34 
—to+t | 5.72 | 5-54 5:79 
9 +to—} 6.32 6.58 jel 
TO +to—]} 6.15 6.59 5.29 
II +to— | 6.07 7.1 5-39 
12 —to+ | 6.09 73 542 
; { —to+] 6.12 7.6 5 47 
J L+to—| 5.97 7-4 5.63 
: —to+ | 6.27 7.6 5:34 
4 +to— | 6.13 7.6 5-40 
15 | —to+} 6.34 77 5-3 
16 | —to+ oI 7.16 5°75 
4 { —to+{ 5.78 Ged 5.68 
tto—{ 5.64 7:3 5-85 
, For 
