252 European Science. [May, 



detached groups. This is the unavoidable result of the subjection of a finite uni- 

 verse of moveable bodies to the law of gravitation, uncompensated by any projec- 

 tile force acting tangentially to the radius of the system. 



The precipitation of meteoric stones upon the earth is, in all probability, another 

 consequence of inadequately restrained gravitation. The cloudy form in which 

 they first appear in the heavens, the light and detonation which precede their fall, 

 and the ignited and occasionally simi-fluid state which they immediately afterwards 

 present, all go to prove that, until their immersion in the earth's atmosphere, and 

 their subjection to its pressure, these bodies existed in a gaseous form, and were 

 cometary satellites of the earth, invisible when at a great distance, by reason of the 

 smallness of their size. It seems therefore reasonable to conclude, that in the 

 event of any portion of a great comet being drawn within the sphere of the earth's 

 attractions, the result would be a precipitation of meteoric dust, and stones of 

 various magnitudes, from the smallest aerolite up to the largest meteoric blocks, 

 such as have been found in Greenland and on the plains of Russia and America. 



A cause, which will accelerate the fall of these bodies, especially of those which 

 confine their gyrations to one sun or planet as a focus, is the long doubted, much 

 ridiculed, but now universally acknowledged ether of Sir Isaac Newton, whose 

 bold and fortunate conjectures regarding the existence of this medium, and the 

 combustibility of the diamond, will ever be remembered, among the proudest tri- 

 umphs of the human intellect. By opposing to the projectile force of these vapou- 

 ry masses a continual resistance, greater* perhaps the nearer to the sun and 

 planets, their centrifugal force will at last be so far weakened that collision with 

 a sun or planet must ensue. As meteoric dust and stones have in all ages fallen 

 upon the earth, so will the comets of Encke andBiELA, now entangled within our 

 sun's exclusive^ attraction, be finally thrown upon that luminary : the chances of 

 their striking a planet or even approaching so near to one as to suffer a deflection 

 of course, which would again throw them out of the solar system, are too minute 

 for calculation. That the dense planets themselves and their satellites similarly 

 suffer a constant retardation, constantly approach their foci, and would in time 

 come in contact with them, cannot be doubted without calling in question the 

 universality and equality of the law of gravitation ; but their comparatively great 

 inertia makes the change so slow as to escape observation, and the major axis of 

 each planet's orbit is practically considered as of invariable length J. 



* Encke's comet has been observed to contract its diameter as it approaches the 

 sun, whence it may be inferred that the etherial medium lias there a greater density, 

 occasioned by its gravitation to the sun, and consequently a greater pressure upon the 

 gaseous mass of the comet, and a more powerful resistance to its motion. 



-|- It may be conjectured that many of the comets of immense period never have 

 their perihelion twice round the same sun, but travel in a zigzag course over the whole 

 extent of our nebula in the milky way ; their projectile force being always sufficiently 

 great to carry them within the attraction of stars different from those where they had 

 their last perihelia. 



+ The resistance of the ether must give an eccentric form to the earth's atmosphere, and 

 increase the pressure upon that side of the earth which is most forward in its orbit. 

 The same resistance must tend to, retard the earth's revolution round its axis, but a 

 counter-balancing agent is here at work — the shrinking of the earth by cooling, which 

 would have an opposite effect. 



