TRANSACTIONS OF THE SECTIONS. 21 



of increase of thickness of deposits. The same must certainly be allowed also at 

 the veiy first, and when cosmic matter is in its most attenuated dust-like state. 



Pressui-e will take place only so long as there is no consolidation of matter. 

 Solid matter presses upon its support, but is steady within itself. The gi-adual 

 evolution of heat is confided to the hearth of pressure. What we observe of risLag 

 temperature as we descend is conducted heat from that hearth, where it is generated, 

 and from which streams of lava are forced up and volcanic action is developed. 



Suppose now a complete solid shell of a very large globe to have been formed, 

 and to be perfectly balanced, and sufiiciently steady to withstand any further ap- 

 proach towards the centi-e. But this shell is still filled with the original cosmic 

 matter, which itself may go on by a similar process to form a new shell concentric 

 to the former one, and developing heat again exactly as in the first instance. A 

 new hearth of volcanic action is thus produced, while the original one becomes ex- 

 tinct. Then the possibility arises, that within this confined space, heat and the 

 expansion of gases might be brought to so high a degree of tension as to break the 

 shell with an actual explosion, as with hollow projectiles fidled with gunpowder, 

 laimching fragments of eveiy size in all possible directions, to travel on tor time 

 unmeasurable through cosmic space. 



What is the reason of the great discrepancy in the density of the celestial bodies 

 of our solar system ? Does this depend only on the elementary substances of which 

 they consist, in a manner analogous to our own earth ; or is that difference founded, 

 partially at least, in the progress of their formation ? We have the densities of 

 Mercury=6-71, of the Earth =-5-44, of Mars=5-15, of Venus=502, of the Moon 

 = 3-37, of the Sun=l-37, of Jupiter=l-29, of Neptune=l-21, of Uranus =0-98, of 

 Satm-n=0-75. 



It is well known that Olbera fii-st conceived the possibility of Ceres and Pallas 

 being fragments of a former larger body. When the asteroids Juno and Vesta had 

 been discovered, Lagrange* gave the numeric conditions of an exploding force under 

 which it might be possible that an exploding planet would yield fragments to be- 

 come comets, or, more properly speaking, to move in orbits of comets, direct or retro- 

 grade, elliptic, parabolic, or when more violent into hyperbolic orbits, to leave our 

 solar system altogether after the first perihelion. Now he found that at the di- 

 stance of a hundred times the distance of the earth from the sim, an exploding force 

 wovdd suffice, giving an unpulse only from twelve to fifteen times greater than the 

 velocity of a cannon-ball — about 1400 feet in one second, which is about the same 

 as the velocity of a point in the equator in the diurnal revolution of om- earth.f 



Although some of the considerations may appear too bold and extravagant, yet 

 I think I have nowhere supposed anything to take place which would not enter 

 within the compass of well-known physical occurrences upon om- own earth. _ I 

 believed it my duty to collect together in a short sketch the considerations which 

 had occuiTed to me, while I have for some time past had an opportimity of ex- 

 amining some facts, and of reporting on others, concerning meteorites. 



I beg leave to lay them before the public, wishing they might induce the friends 

 of scientific progress to take a still more lively interest both in observing facts and 

 in collecting materials (by publishing the former and preserving the latter in the 

 leading Museums) relative to these cmious celestial bodies, in order to advance our 

 ideas in these as yet comparatively obscure branches of science. 



Finally, I may be pei-mitted to recapitulate the entire series of steps in the pro- 

 gress of the formation of meteorites. 



I. Original Formation. 



1. The creation of matter — atoms of elements as they are familial' to us, in their 

 nascent state. 



* Sur rOrigine des Cometes. — Connaissance des Tems pour I'an 1814, p. 211. 



t If it were assimied as a plausible hypothesis that lieaxenly bodies in the manner above 

 alluded to might fly into pieces, having their fragments transformed into planets, asteroids, 

 or aerolites, then one step further might bring in connexion with the same explosions also 

 the origin of comets. The solid crust of the sheU would supply more solid bodies, wliile 

 the aerial portion and the finest dust-like residue, being isolated in cosmic space, but still 

 acted upon by gravitation (in so far as it would not disperse altogether, having also received' 

 an impetus or launch in one direction), would assume the shape and nature of a comet ! 



