272 
by the plum-line, which has always been 
fuppofed to have a direét and invariable 
tendency towards the center of the earth, 
in all latitudes ; and even fince it has been 
difcovered that the earth is an oblate 
{pheroid, or the diameter of the Equator. 
longer.than the polar axis, it has been con- 
cluded that the dire&tion in which bodies 
defcend is accurately perpendicular to the 
furface of the earth and fea, yet it would 
be impeMfible, fays Mr. Dunn, to find the 
longitude either at fea or land, within 
thirty geographical miles of the truth, 
without making ule of a. corrections as 
he tuggefis in his tr peo. Wele coles- 
ticns are deduced from the following 
principles :—-1ft, If the earth be conidered 
as a perie&t {phere or glcbe of folid and 
homogeneous matter and at reft, a bedy 
let fail towards the earth, will move ina 
right line towards the earth’s center, be- 
caufe the quantity of matter and the 
quantity of attraétions in the northern, 
fouthern, eaftern, and weftern hemifpheres 
are exaGtly mutual and equal to each other. 
zd, Suppofe this globe to continue folic 
and to have a motion round its polar axis 
once in 24 hours, then will this falling 
body be impelled by two forces, one tend- 
ing towards the center, the other in the di- 
rection of the centrifugal force. But it is 
known that when a body is ‘af&tedupen by 
two forces under different dire&tions, it will 
defcribe the diagonal of a parallelogram 
between both thefe direétions. 
quently the falling body, fuppofing the 
earth a perfect {phere in motion round its 
polar axis, would not move ina right line, 
towards the center-of the earth, but towards 
a point fituated to the eafievard of that 
center, fuppofing too that the diurnal ro- 
tation is performed in a dire&tion from 
weft to eaft.—3d, Suppofe the earth ta be 
a fpheroid, flat tewards the poles and at 
reft, a falling body will not move ina right 
line towards the earth’s center, becau/e the 
quantity of matter in the northern and 
feuthern hemifpheres will, except ander the 
equator and at the poles, be unequal, and 
confequently the falling body will move in 
‘a line towards a point fituated to the fouth- 
ward or northward of the center, according 
as the defcending body was either in north 
or fouth latitude. . That is, the point to 
which the line of dire&tion tends will be 
to the fouthward of the center when the 
failing body isin north latitude, and to 
rhe northward when in fouth latitude.--4th, 
Suppoie this Spheroidal earth to be turn- 
ing from wet to eaft round its polar axis, 
then will the falling body be impelled by 
two forces as before in the {pherical earth 
Principles and Calculations of Falling Bodies. 
Confe-’ 
[May 
and will move in the diagonal of a paral- 
lelogram formed by thefe two forces. 
Hence.a deviation not only in longitude, 
but alfo in latitude will take place from 
the true and abfolute perpendicular. ; 
On thefe principles Mr. Dunn founded 
thofe correétions already noticed ; and he 
alfo found that the dire&tion of a plumb-line 
at Greenwich is 14/15 different from a 
right iize dyawn perpendicular to the furface 
of theearth. 
I am,Sir, yours, &c. &c. 
Edinburgh, April 5, 1799. Se dat 
= See 
To the Editor of the Monthly Magazine. 
SIR 
OUR correfpondent W. S. on falling 
bedies page 96, muft have pleafeg many 
of your readers, but had he given an exam- 
ple by -way of illutration he would have 
pleated them more; that tafk be mine.— 
247 feet French are equal to 263,433 
feet Englith, or 43,3 fathoms, from which 
height a heavy body will fall in 4,045 
feconds. 
made his experiments at Paris, the length 
of a degree of longitnde there, according 
to-Gen. Le Roy, is 40363,2 fathoms, and 
the femidiameter of a iegment of the globe 
in the latitude of Paris is 2309233,3 
fathoms, to which, adding the height of 
the tower 43,3 fathoms, gives the encreafed 
diameter 2309276,6 fathoms. Then, as 
240 feconds, the time of revolution of one 
degree of the earth's motion, is to 40303,2 
fathoms, or one degree in the latitude of 
Paris, fois 4,ca5 feconds, to 679,277 -fa- 
thoms, the motion of a point on the earth at 
Paris. Again—as 2309233,3: 679527733 
2309276,5: 679,29 fathoms, the fpace a 
point will move through at the height of 
263,433 feet, the point ot fufpenfion at the 
top of the tower.’ The difference of the 
motions on the earth and point of fufpen- 
fion is 0,013 fathoms or 0,936 inches, 
the quantity the body will fall to the 
eaftward of a plumb-line, which reduced 
into French lines, is 8,77; and. Mr. Dr La- 
LANDE by experiment makes it 8,5 lines, 
EDMONTONIENSIS, 
ome eo 
To the Editor of the Monthly Magazine. 
SIRy 
T FEEL myfelf much indebted to your 
4. correfpondent (a Pra@tical Farmer) for 
his valuable communication in your laf 
Magazine, in aniwer to my queries. 
He aiks, “Is it the praétice to winter 
fheep on wet clays?” I have and da 
practice this methed, though Tam by na 
Teans partial to it; but where good turnip 
land is not to be had, as in my cafe, it is 
perhaps the beft way of keeping theep ~ 
efpecially 
Now fuppofing De LALANDE - 
