JO!) 
M O T 
by the orbicular motion, through 100,000 feet to B, in 
the diagonal E B. Such a diagonal courfe as A E is 
therefore, in point of fact, generated by every projectile, 
while it is riling to any given height in the atrfiofphere; 
but, as the fpeCtator is carried with the projeCtile, he 
merely meafures its novel and peculiar motions, and is 
incapable of obferving the orbicular motion, of which 
lie partakes in common with the projeCtile. The pro¬ 
jectile is not, however, the lefs fubjeCt to the force of the 
orbicular motion, becaufe it is not perceived or felt by a 
fpeCtator at reft ; but, as a body put into motion by 
novel forces, acting in oppofing directions, its novel ftate of 
oppoiing motion is liable to be affe&ed by all oppofing 
forces ftimultaneoufly exifting in nature; and, when its 
novel force is exhaufted or deftroyed at E, it becomes the 
patient of the great natural forces, which, in moving the 
earth and atmofphere from A to B, move it likewife, as 
part of the fyftem. 
The projeCtile having however afcended to E, a dif¬ 
ficulty arifes in regard to the origin of the force which 
defleCts it from the fummit at E towards B„ Why does 
it not move for ever in the parallel DE? What is the 
original force that turns it afide ? Is that force required 
to be equal to the weight of the body ; or what proportion 
of that force, and how is it generated ? 
It appears by the faCt, that the whole force which was 
neceflary to caufe it to fall through the 16feet, is but 
a 6oooth part of the orbicular momentum ; confequently 
the defleCtion of 16 feet forms but an angle of 20 feconds 
at A and at B. The nafcent defleCtion, however, at E, 
would be but an infinitefimal of the laid 20 feconds; 
confequently, any indefinitely-fmall defleCtive force, 
arifing from new combinations of the forces, might be 
fufficient to return a body to the earth. What then is 
the aClual defleCtive force which turns a projeCtile down¬ 
ward, and prevents it from moving for ever in the place 
in the atmofphere in which it has been left by the ex¬ 
tinction of that projeCtile force, which carried it from 
the furface into fo novel a fituation in the atmofphere ? 
Let us examine all the circumftances in which the 
body has been placed : 
1. It was moving with the earth in its orbit with all 
other bodies upon the earth, and therefore poflefled a 
momentum in that direction, which, with regard to other 
bodies, was as their quantities of matter. 
2. It was deflected afide by fome novel mufcular or ex- 
plofive force, and thrown towards D. 
3. But, while it was moving towards D, or 16 feet and 
an inch, it was carried 6000 times as far, or 100,000 feet, 
at right angles; and therefore performed a diagonal. 
4. At C it lofes its force in the direction at D, and is 
defleCted towards the earth, at B. 
Let us. now examine what other circumftances have 
attended its afcent: 
1. Its paflage has been made in a refilling medium, 
which tended, as is known, conftantly to deftroy the 
force with which it was projected from A towards D. 
2. During its afcent, the point A, and every point of 
the diagonal A E, were all'o performing a rotary circular 
motion round the centre of the earth. 
3. The point A would therefore be defleCted down¬ 
ward, during its paflage towards C, from A below C; 
fo that D would alfo be defleCted below E, and the 
entire line A E would be defleCted, or turned downward, 
below A C. 
4. The. rotary motion would therefore have the effeCt 
of deflecting the body below the diagonal A E, at every 
increment of its afcent. 
5. The conftant refiftance of the atmofphere would, 
in like manner, defleCt it. 
6. The body would, therefore, be fubjeCt, during its 
afcent, to the aCtion of four forces: a, the orbicular 
force; b, the projeCtile force; c, the rotary force; d, the 
refitting force. 
Vol. XVI. No. 1097. 
I O N. 
7. At the apex, the projeCtile and refilling forces having 
deftroyed each other, the body is then furrendered to 
the joint aCtion of the orbicular force and the rotary 
force. 
8. And we have feen that it is the effeCt of the rotary 
force to defleCt it from the right line of the orbicular 
force towards the earth. 
Confequently, it is the rotation of the earth and at¬ 
mofphere, aCting fimultaneoufly with the annual motion, 
which produces the defleCtion of bodies from the right 
line of their orbicular motion ; but the circular rotation 
has another important effeCt on the mafles of, various 
denfity which compofe the earth, and which, as fubjeCt 
to a common force, would have different orbicular velo¬ 
cities, but for the effeCt of their common rotary motion 
in circles of different radii. 
It feems extraordinary that, although the two-fold 
motion of the earth has fo long been known and admitted, 
no mechanical effeCts Ihould have been confidered as 
arifing among its parts from the operation of thofe mo¬ 
tions ; and that one motion Ihould have been confidered 
as having no other end than the alternation of feafons, 
and the other none but the changes of day and night. 
It is true that thefe are fome of the ends rel'ulting from 
the two-fold motion; but general caufes have many 
effeCts, and thefe are rather confequential than proximate. 
The proximate effeCt of motion is force, tfle proximate 
effeCt of force is the communication of motion, force, 
and momentum ; and in this inftance the motions of the 
earth produce in the parts motion, force, and momenta ; 
which, diverted, defleCted, or turned afide, by any foreign 
mufcular, mechanical, or explofive, force, produces the 
phenomena of refiftance and weight. 
To the rotary motion of the earth is, therefore, to be 
referred that uniformity in the velocity of bodies of 
various denfity which enables the whole to keep an equal 
and uniform pace in the orbit of the earth. It is this 
rotary motion which reduces to order, what otherwife 
would be chaos. Hence it is that all fluids are impelled 
into a level furface; hence too, doubtlefs, it has been, 
that mafles of the fame denfity have formed themfelves 
into ftrata while in a ftate of folution; hence arife all 
the phenomena which refult from any difturbance in the 
order of denfity; and hence it is, that, when a heavy 
body is thrown into lighter fluids—as air or water, the 
general law is proved by phenomena exactly proportioned 
to the relations of denfity. 
We know, from the diurnal phenomena, that the earth 
and atmofphere have fuch a common rotary motion; and 
w r e know, from their common orbicular force, that the 
whole have unequal momenta. It is, however, a necef- 
fary mechanical effect of a common rotary motion, pro¬ 
ducing, of courfe, equal momenta in mafles of various 
denfity, that they range themfelves, or feek to range 
themfelves, in concentric circles, or radii of rotation, 
inverfely as their refpeCtive denfities. The lighter bodies 
wall be projected from the centre towards the circumfer¬ 
ence, and the heavy ones will be forced towards the centre 
by their mutual collifions. Such will be the law, govern¬ 
ing all the mafles that are free, to move one among an¬ 
other, as the fluid parts and the moving or moveable 
parts. It is a law growing out of the conditions; and 
the conditions are thofe which exift in nature. If a pro¬ 
jeCtile, therefore, have a fpecific denfity equal to the air 
or fluid into which it has rifen, it will be carried round 
the earth in the concentric circle of that ftratum, becaufe 
the momenta are there equal; but, if it be lighter than 
the air, it will then be reflected by the denfer itrata, till 
its own momentum and the momenta of the furround¬ 
ing air be equal; while, on the other hand, if it be heavier 
than the circumambient air or fluid, then the air or fluid 
will rife over it and deflect it to the earth, with a force 
which will be nearly in the ratio of their denfities. 
Galileo was the firft geometrician who analyzed the 
F f phenomen* 
