112 ' MOT 
nent influence of tlie pre-exifting orbicular and rotary 
forces in the lines of their direction, and the refulting line 
of motion is the effect of all the operative forces. 
6. That the phenomena of the afcent and defcent of 
bodies is alfo influenced by the reflftance of the medium 
through which its novel direction of motion has forced 
it to proceed. 
7. The force with which the defleCtion by the rotary 
motion is produced, is as the denfity of the body deflected 
to the denfity of the medium in which it moves, and in the 
inverfe ratio of the fquares of the diftance from the centre. 
8. That it is the neceflary tendency of the rotary mo¬ 
tion to give an equal momentum to the heterogeneous 
malTes compofing a planet and its atmofphere, while the 
whole are moving with an equal velocity in the orbit. 
9. That all phenomena of motion vifible to beings who 
partake of the common motions of a planetary fyftem, are 
either the relative motions of diftant orbs, or the difturb- 
ance of the great common motions by new directions of 
motion produced by fome mufcular, mechanical, explo- 
five, or chemical, force. 
10. That thefe temporary and novel directions of force 
and motion are fpeedily extinguiflied by the great perma¬ 
nent forces moving in other directions, all traceable to the 
phenomena, and producing compofitions of motion which 
refult from the known laws of dynamics. 
11. That of courfe fimilar motions produce fimilar 
phenomena in all planetary bodies. 
12. That, therefore, the phenomena hitherto afcribed to an 
occult power called gravitation, is a fimple refult of known 
motions.'" 
In a fubfequent Number, the author has^ undertaken 
to reply to certain “ objections,” w’hich, he fays, “ have 
been flatted by various perfons, in converiation, and 
through the public prefs.” 
I. It has been doubted whether bodies would fall in the 
exhaufted receiver of an air-pump upon this hypothefis.— 
“ To this it may be replied, that the exhaufted receiver, 
the contained vacuum, and the bodies let fall before and 
at the inftant of fall, are all of them as much the patients 
of the orbicular and rotary motions, as though no fuch 
exhauftion had taken place. The orbicular motion w\as 
carrying forward the whole, and the rotary motion was 
endeavouring to defied every part of the fuftained mafs 
from the right line of the orbicular motion. The differ¬ 
ence arifing from the abfence of the air is the fame, what¬ 
ever might be the fource of the power which caufed the 
bodies to fall ; that is, a feather would fall in the fame 
time as a guinea, Amply becaufe the atmofphere oppofed 
no reflftance, whether the centripetal force was produced 
by governing motions or by attraction.” 
II. It is objected that a projeCtile would continue to 
afeend for ever, unlefs the force of attraction drew it to¬ 
wards the earth .—“ To this I reply, that the defective 
force of the rotary motion is equivalent, in the retarda¬ 
tion of a projeCtile, to the fuppoled attraction ; and that,' 
in, combination with the reflftance of the atmofphere, 
that defleCtive force produces all the phenomena of pro¬ 
jectiles, the orbicular force being common to both hypo- 
thefes.” 
III. It has been objected that, if a body were let fall 
in the atmofphere, it would either go off in a tangent 
into fpace, or would move for ever in that place, but for 
the earth’s attraction .—“ In regard to the aflertion, that 
it might move off in a tangent, it need only be confidered, 
that no force has been given it in the direction of fuch 
tangent, and that bodies do not move in any required 
direction without fome force exerted in that direction. 
And, that it will not move for ever in an unfupported 
fpot in the atmofphere, arifes from the influence of the 
deflecting rotary motion, of which it partook when placed 
there, in which it continues, and which it alfo derives 
from the furrounding medium.” 
IV. It is contended that the Galilean laws of falling 
bodies cannot be accounted for, except on the principle 
ION. 
of a continually-aCting attraction.— “ To this I reply, 
that the great terreftrial motions are, in like manner, con¬ 
tinually acting; and that from like caufes they mult pro¬ 
duce like phenomena whenever any body is placed in 
circumftances to become the fenfible patient of their ac¬ 
tivity.” 
V. It is urged, that local affeCtions of mountains, or 
other maffes, can refult only from tile attractive influence 
of thofe maffes; and the experiments of Malkelyne and 
Hutton, of Bouguer, of Zach, and of Cavendifh, are ad¬ 
duced as proofs.—“ A mighty holt, if their acumen and 
their accuracy bore on the queftion. But, as I refer ail 
phenomena to a centre of motion, and the Newtonians re¬ 
fer them to a centre of attraction; and as both centres are 
generated by the aCtual difpoiitions of all the maffes of 
the aggregate ; fo both centres are varied in pofition by 
unequal arrangements of the maffes; and the motions on 
the furface referable to fuch centres are varied according¬ 
ly, and in equal degrees, upon both hypothefes. 
“ If the earth were an equal and homogeneous fphere, 
then all the phenomena of falling or fulpended bodies 
would have reference to the mathematical centre of the 
mafs, and the plumb-line would always'hang perpendicu¬ 
larly to the vifible horizon; but, if a mountain, or any 
unequal mafs, be placed on the furface, then on one hy¬ 
pothefis the centre of the motion, or on the other the 
centre of the attraction, will be railed above the mathe¬ 
matical centre, in a certain proportion, towards that 
mountain, creating a new phylical centre; and all the 
defleftions of the rotary motion on this theory, or all the 
attractions on the Newtonian theory, will be made with 
reference to that new’ centre. The maximum of varia¬ 
tion will take place neareft to the projecting mafs; and, 
if the mafs were fuddenly created, or brought near a fuf- 
pended plummet, it would turn it afide, in a given pro¬ 
portion of the bulk of the mafs to the bulk of the earth ; 
and, as in Mr. Cavendilh’s experiment, it might perhaps 
be poflible to meafure the impulfe. But, in every poflible 
cafe of fuch inequalities, the fame phenomena mult and 
would refult from thus varying the centre of the aggre¬ 
gate; whether the phenomena w’ere afcribed, as now, to 
the efficient and operative motions of the earth, or, as 
heretofore, to the principle called by the name of at¬ 
traction. 
“ I have taken it for granted that thefe experiments 
and calculations are corred, becaufe the true refults mult 
be included in the laws of motion, as well as thofe of 
gravitation; but I remark, with profound deference to 
the learned calculators, that the Schehallien refult af- 
fuines two-thirds of the circumference for the earth’s 
attraction as a quantity admitted; and, in Mr. Cavendilh’s 
leaden-balls experiment, the earth’s attraction is ajjumed 
to be reprefented by its diameter—that is, in both cafes, 
a quantity unknown, and growing out of the hy’pothelis 
of gravity, is taken for granted to prove that very gra¬ 
vity. If the known bulk, force, and denfity, of the 
mountain and the balls were, by exaCt analogy, to be 
compared v/ith the known bulk of the earth, to deter¬ 
mine its force and denfity, then the refults will be to¬ 
tally different, and the irrelevancy of the experiments 
would be manifeft.” 
VI. It is urged, that, as attradion is admitted to pro¬ 
duce certain phenomena in eledricity, galvanifm, che- 
miftry, magnetifm, and optics, fo the attraction of gra¬ 
vitation is but an analogous power, and might, in like 
manner, be admitted .—“ This argument to fay the leaft 
of it, is a very indirect one, and includes a large appeal 
to faith. I fay again, with little danger of refutation, 
that the terms attraction and gravitation were chimeras 
of the middle ages, growing out of the fchools of aftro- 
logy and magic; and, in the writings of the iliuftrious 
Newton, are akin to the ghofts of the equally-illuftrious 
Shakefpeare, or to the fympathies which filled the heads 
of all philofophers in thofe days. They may be ufed like 
characters in an algebraic equation; but it is incorreCt to 
fubftitut* 
