M O T 
fubftitute them for real quantities, or efficient caufes, or 
to let them up in opposition to the operative powers of 
nature, when thefe are found to be fufficient to explain 
phenomena. Nothing, in truth, has tended more to re¬ 
tard the progrefs of fcience than thus flopping at the phe¬ 
nomena of attraftion, and then impioufly treating this 
fecondary caufe as the proximate effebl of omnipotent 
agency, though it is found to aft mechanically and fub- 
ordiuately, according to certain laws of diftance.” 
VII. It is objected that this illuftration of the caufe of 
terreftrial gravitation tends to overturn the Newtonian 
philofophy, which is built on the immutable bafes of 
geometry.— 14 To this I reply, that, as the great Newton 
did not affect to explain this caufe, but merely admitted 
this name of the effect, fo any hypothefis which feeks to 
account for it can have no neceffary o.ppofition to his 
lyttem. At the lame time there is a latent though po¬ 
pular error, in confounding phyfics and geometry: for 
all phyfical effefts refult from competent proximate 
caufes, often varying; and all geometrical laws refult 
from relations, always fixed. But, if our excellent phi- 
lofopheV fo well accounted for the phenomena of the fo- 
lar fyftem by geometry, founded on the balls of an oc¬ 
cult principle, with how' much more fatisfaftion would 
he have done it oh a mechanical bafis ? The author of 
this hypothefis has calculated,, however, on no change 
but in nomenclature.” 
VIII. It is afferted, that, as gravitation is a fiat of 
Omnipotence, fo to attempt to account for it is beyond 
the due bounds of philofophical inquiry.—“ Without in¬ 
tending any perfonal difrefpeft to thofe who have ufed 
this argument, it may be afferted, that fuch has been the 
prejudice of ignorance, from the age in which man firft 
ufed a fpade to augment the natural productions of the 
earth, to the days of Galileo, and even to our time, ’when 
Jenner difeovered the means of extirpating a fatal difeafe. 
Shall we more nearly approach the Caufe of Caufes in 
determining the mechanifm by which a planet is held to¬ 
gether, or by which a fyftem moves, than by inveftigating 
the circulation of the blood, or by the chemical analyfis 
of any fubftance in Nature? The caufes of motion 
would ftill remain behind, and, were a future age to dis¬ 
cover thefe, the prime mover of all things, the fublime 
and incomprehenfible Creator and Preferver, w'ould ftill 
be at an infinite diftance from the finite powers of man !” 
IX. It is afferted that the law of gravitation is not 
proved to be the law of motion.—“ To prove the affirma¬ 
tive of this propofition was, however, the entire bufinefs 
of the Principia of Newton, and has been the employ¬ 
ment of all mathematicians from his time to our own. 
If the laws of motion are not the laws of gravitation, then 
have philofophers been dreaming during the laft hundred 
years. I merely identify w'hat they have proved ; and, as 
mathematicians have, by the hypothefis of gravitation, 
proved the laws of motion, I now delire to difeard the 
unknown or affumed quantity, and to reftore the known 
motions of nature in its place—for the purpofe of ex¬ 
plaining the modus operandi by which the phenomena are 
produced. 
“ It is imagined (fee Philofophical Magazine for Au- 
guft) that I had forgotten the relations of radii and cir¬ 
cles ; I was not, however, alluding to circles, but to the 
furfaces of concentric fpheres, which were the objefts of 
difeuffion, and which are to each other as the fquares of 
their radii. The /paces generated on fpherical furfaces 
being to each other as the fquares of their radii, it follows 
that the quantities of motion generated in each ftratum, 
and the forces generating thole motions, are in the fame 
ratio. On this point there is nothing to add or to alter. If 
the concentric ftrata were in denlity reciprocally as the 
fquares of their diftances, and undilturbed, there would 
be no phenomena; but it is the difturbance of that which 
lias been in a ftate of equilibrium (either by diftance from 
the centre, or by the refiftance of friftion), which occa¬ 
sions the fenfible phenomena of weight, or of falling 
VOL.XVI. No. io 97 . “ ° 
r o N. 113 
bodies. I do not, however, confider that thefe obferva- 
tions conclude the fubjeft: fori admit, that ail thecircum- 
ftances which exift among the parts of a fphere, moving in 
an orbit, the momenta of whofe maffes in the concentric 
ftrata are equalized by a rotary motion; as-well as the ef- 
.fefts ariling from the centre of denlity not being the ma¬ 
thematical centre ; and alfo from accidental difturbance.; 
in the equilibrium of particular bodies; merit the careful 
analyfis of philofophical mathematicians. At the lame 
time, although the mathematical laws mull neceffarily be 
the lame, it is not indifferent, in human inquiries, whe¬ 
ther phyfical phenomena are aferibed generally to gravi¬ 
tation, of which nothing is affefted to be known, or to 
motion, of which we may not know the primary origin. 
We know, at any rate, more of motion than vve know of 
gravitation. Belides the laws common to both, we know 
that motion is an accident of bodies which gives them 
momenta, and caufes them to change their fituations' in 
fpace; and we know that fome motions are general, an¬ 
tecedent, or primary,and that others are local, conlequent, 
or fubordinate. In the problem before us, we are there¬ 
fore enabled to (how that known effefts are conlequences 
of leveral known motions, thereby attaining a degree of 
analyfis, which could never be eftefted, if we referred the 
fame phenomena to the general name of gravitation.” 
ConcluJwn.— Thefe, I believe, are the chief objections 
which have been imagined and promulgated in oppofition 
to a theory which fubftitutes the known motions of nature 
as operative caufes of certain phyfical phenomena, in place 
of an affumed principle called gravitation, by which, falfe 
analogies have been introduced into philofophy, and ef¬ 
fefts aferibed to a caufe neither proximate nor in contact. 
It may be difficult to analyfe, in like manner, the motions 
which produce all the celeftial phenomena, or trace the 
fources of particular motions; and it may be impoftible 
for man to afeertain any other origin of motion than the 
fublime Caufe or Caufes ; but we advance another ftep in 
human knowledge when we difeover that the two-fold 
motions of a planet are competent to the confolidation 
and unity of its mafs, and are efficient caufes, by means of 
which, bodies removed out of their equilibrium are re- 
ftored to the mafs. Monthly Mag. July and Sept. 1817. 
Motion, perpetual, in mechanics, a motion which is 
fupplied and renewed from itfelf without the intervention 
of any external caufe ; or it is an uninterrupted commu¬ 
nication of the fame degree of motion from one part of 
matter to another, in a circle or other curve returning 
into itfelf, fo that the lame momentum ftill returns undi- 
miniftied upon the firft mover. 
This celebrated problem of a perpetual motion confifts 
in the inventing of a machine, which has the principle of 
its motion within itfelf. M. de la Hire has demonftrated 
the impoffibility of any fuch machine, and finds that it 
amounts to this, viz. to find a body which is both hea¬ 
vier and lighter at the fame time; or to find a body which 
is heavier than itfelf. 
To find a perpetual motion, or to conftruft an engine. 
See. which (hall have fuch a motion, is a famous problem 
that has employed the mathematicians of two thoufand 
years; though none, perhaps, have profecuted it with at¬ 
tention and earneftnefs equal to thofe of the prefent age. 
Infinite are the fchemes, defigns, plans, engines, wheels, 
&c. to which this longed-for perpetual motion has given 
birth : it were as endlefs as impertinent to give a detail of 
them all. In effeft, there feems but little in nature to 
countenance all this affiduity and expeftation ; among all 
the law's of matter and motion, we know of none yet, 
which feem to furnilh any principle or foundation for 
fuch an effeft. 
Aftion and re-aftion are allowed to be ever equal; and 
a body which gives any quantity of motion to another, 
always loles juft fo much of its own ; but, under the pre¬ 
fent ftate of things, the refiftance of the air, the friftion 
of the parts of machines, &c. do neceffarily' retard every 
motion. To keep the motion conllant, therefore, either, 
G g firlt, 
