506 P L A 
gular progrefiion in the distances of the planets, and a 
general harmony in the form and pofition of their orbits. 
■Thus does the ingenious Dr. Brewfter introduce his ge¬ 
neral reafoning on this fubject. He then proceeds to 
obferve, that the elements of the new planets furnifh us 
with feveral direct arguments, drawn from the excentri- 
city and inclination of their orbits, and from the pofition 
of their perihelia and nodes, and all concurring to Ihow, 
that the four new planets have diverged from one point 
of fpace, and have, therefore, been originally combined 
in a larger body. When the original planet burft in 
pieces by fome internal force capable of overcoming the 
mutual attraction of the fragments, the larger fragment 
mult obvioufly receive the leaf!: impetus from the explo¬ 
sive force, and circulate in an orbit deviating lefs than 
any other of the fragments from the original path of the 
large planet; while the Smaller fragments, being thrown 
off with greater velocity, would revolve in orbits more 
excentric, and more inclined to the ecliptic. Applying 
this remark to the cafe before us, the excentricity of Ceres 
and Vefta is nearly one-twelfth of their mean diftance, 
that of Ceres being rather the greatest ; and the excentri¬ 
city of Pallas and Juno is one-fourth of their mean diftance, 
that of Pallas being a little greater than that of Juno. 
From the theory it might be expedied, that Pallas and 
Juno would be considerably Smaller than Ceres and Vefta, 
and that Ceres lhould be the larger fragment, and have 
an orbit more analogous in excentricity and inclination 
than any of the finaller fragments to the other planets of 
the fyfte'm. As far as the diameters of the new planets 
have been meafured, the theory is very Strikingly con¬ 
firmed by obfervation. According to Dr. Herfchel, the 
diameter of Ceres is 163 miles, while that of Pallas is only 
So. The observations of Schroeter make Juno consider¬ 
ably lefs than Ceres; and, though the diameter of Velta 
has not been accurately ascertained, yet the intenfity of 
its light, and the circumftance of its being diftin&ly visi¬ 
ble to the naked eye, are Strong proofs that it exceeds in 
magnitude both Pallas and Juno. The Striking refem- 
blanc’e between the two Smaller fragments, Pallas and 
Juno, in their magnitudes, and in the extreme excentri¬ 
city of their orbits, would lead us to anticipate limilar 
refemblances in the position of their nodes, in the place 
of their perihelia, and in the inclination of their orbits; 
■while the elements of Ceres and Vefta Should exhibit 
Similar coincidences. Now, the inclination of Ceres is 
io c , and that of Velta 7 0 ; while the inclination of Juno 
is 21 0 , and that of Pallas 34°; the two greater fragments 
having nearly the fame inclination, and keeping near rhe 
ecliptic, while the fmaller fragments diverge from the 
original path, and rife to a great height above the eclip¬ 
tic, and far above the orbits of all the other planets in 
the fyftem. Ifir Shall be found, from obfervation, that 
Vefta is one of the fmaller fragments, we may then ac¬ 
count for its pofition with regard to Ceres, and for the 
Small inclination and excentricity of its orbit, by fuppo- 
Sing the planets Ceres, Pallas, and Juno, to have diverged 
in the Same plane, and nearly at right angles to the eclip¬ 
tic, while Vefta diverged from the direction of the ori¬ 
ginal planet in a plane parallel with the ecliptic. This 
opinion is ftrongly confirmed by the faff, that the orbit 
of Vefta is nearer to the fun than either of the orbits of 
the other three fragments. The fame coincidence is ap¬ 
parent in the pofition of the nodes. The orbits of Pallas 
and Juno cut the ecliptic in the Same point, and the nodes 
of Ceres and Vefta are not far diltant. If all the frag¬ 
ments of the original planet had, after the explofion, 
b£.en attracted to the larger fragment, it is obvious that 
they would all move in the fame orbit, and confequently 
liave the fame perihelion. If the fragments received a 
llight degree of divergency from the explofive force, and 
moved in feparate orbits, the points of their perihelion 
would not coincide, and their reparation would increafe 
with the divergency of the fragments. But, Since all the 
fragments partook of the motion of the primitive planet, 
the angle of divergency could never be very great; and. 
NET. 
therefore, we fnould expect that all the perihelia of the 
new planets would be in the fame quarter of the heavens. 
This theoretical deduction is 1110ft wonderfully confirmed 
by observation. Thefe Singular refemblances, as our au¬ 
thor clofes his reafoning on this fubjedt, in the motions 
of the greater fragments and in thofe of the fmaller frag¬ 
ments, and the Striking coincidences between theory and 
obfervation in the excentricity of their orbits, in their 
inclination to the ecliptic, in the pofition of their nodes, 
and in the places of their perihelia, are phenomena which 
could not poffibly refult from chance, and which concur 
to prove, with an evidence amounting almoft to demon¬ 
stration, that the four new planets Slave diverged from one 
common node, and have therefore compofed a Single pla¬ 
ner. See Fergufon’s Astronomy, by Dr. BrewSter, vol. ii. 
The theory which afcribes the Subordinate motions on 
the earth to its fuperior motions as a planet, (See the arti¬ 
cle Motion, vol. xvi.) is oppofed by many perfons, who, 
afifuming that the motions of the planets in a fyftem are 
governed by gravitation, afcribe incongruity to a new 
dodtrine which excludes that principle from the internal 
or local phenomena of a planet. 
The author of that theory (fir Rd. Phillips) is, how¬ 
ever, of a totally different opinion. He believes in the 
perfedt harmony of nature; in the exadt analogy of 
caufes and eft’edts; and, wherever he fees motion, he af¬ 
cribes it toother motion afcending in a Series ad infinitum, 
or to an unknown caufe. He therefore gives no credit 
whatever to the existence of any univerfal principle of 
Caufation, fuch as that called by the name of gravitation ; 
but refers all phenomena to motion, primarily and proxi- 
niately. . • 
It is lefs eafy to demonstrate that difcant planets move 
one another by impulfe, than it is to Show that loofe bo¬ 
dies in a Ship, or on the earth, are governed in their 
fubordinate phenomena by the paramount motions of the 
Ship or earth. Every one capable of understanding its 
terms mult feel as an axiom, “ that the orbicular and ro¬ 
tary motions of the earth necefiarily give weight to bo¬ 
dies, and laws to their fall, becaufe the moving earth and 
the bodies are in contad'f, and partaking of thofe common 
motions;” but certain poftulata muft be granted before 
it can be proved to beings whofe experience is confined 
to the Subordinate phenomena of the earth, that difuni- 
ted planets and maifes can operate on each other mecha¬ 
nically, and communicate motion to one another. 
The poftulata required to be admitted are as under: 
x. That all Jpace is filled withJome gafeous medium. —Ira 
the age of Kepler and Newton, the discoveries of Prieft- 
ley had not proved the existence of various gafes. An 
incompreSfible fluid, fo light as hydrogen, was not then 
known to exilt. The limilar phenomena of the planets ; 
the combustion of meteors at great heights; the tranf- 
miflion of folar and planetary light, and the refledtion of 
the folar light after it has been refradted through the at- 
mofphere of a comet; prove, however, that fome rare me¬ 
dium adtually fills fpace; even if its existence were non 
futficiently proved by the mechanical phenomena of the 
planets. 
z. The medium of [pace is aEled upon in firaight lines by 
moving bodies placed within it. —It is difficult for men who 
are accustomed to See the connexion of rods or levers of 
fixed continuous matter between bodies adting on one 
another, to conceive that any gas, like hydrogen, can adc 
by like agency. But this power of gas will be evident 
on flight consideration ; for, if a tube or Series of tubes, of 
ten feet or a million of feet in length, were filled with hy¬ 
drogen gas, and a plug were driven into one end, fo as to 
require any known power lefs than the Strength of the 
tubes to force it out; then, ifapifton were forced with 
that degree of power into the other end, it is notorious 
that the rarelt gas would expel the plug as eftedtually as 
though it were propelled by a continuous rod of iron. 
If fpace, therefore, be full of any light gas, or fluid fui 
generis, it is evident that fuch gas, in luch a plenum, muft 
adt in continuity in filled fpace, as well as in a filled tube. 
3 We 
