NEBULOUS STATE OF MATTER. 23 



with the velocity of the motion. In addition to the dis- 

 integration which would arise from the tendency of the 

 atoms to fly from the centre, the motion, in space, of 

 the planetary mass would naturally occasion a trailing 

 out, and the only degree of uniformity which this orb 

 could, under these imaginary conditions, possibly pre- 

 sent, would be derived from the combined effects of 

 motions in different directions. 



Amid the remoter stars, some remarkable cloud-like 

 appearances are discovered. These nebulae, presenting 

 to the eye of the observer only a gleaming light, as from 

 some phosphorescent vapour, were long regarded as 

 indications of such a condition as that which we have 

 just been considering. Astronomers saw, in those mys- 

 terious nebulae, a confirmation of their views, which 

 regarded all the orbs of the firmament as having once 

 been thin sheets of vapour, which had gradually, from 

 irregular bodies traversing space, been slowly condensed 

 about a centre, and brought within the limits of aggre- 

 gating agencies, until, after the lapse of ages, they 

 become sphered stars, moving in harmony amid the 

 bright host of heaven.* Geologists seized on those 



the largest portion of tins heat will be given to the displaced air, 

 every particle of which will sustain the shock, whilst only the sur- 

 face of the stone will be in violent colJision with the atmosphere. 

 Hence the stone maybe considered as placed in a blast of intensely 

 heated air, the heat being communicated from the surface to the 

 centre by conduction. Only a small portion of the heat evolved 

 will therefore be received by the stone; but if we estimate it at 

 only T ^y it will still be equal to 1 Fahrenheit per 69,679 Ibs. of 

 water, a quantity quite equal to the melting and dissipation of any 

 materials of which it maybe composed. Mr. J. P. Joule, On Shoot- 

 ing Stars: Phil. Mag. No. 216, p. 348. 



* " Laplace conjectures that in the original condition of the solar 

 system, the sun revolved upon his axis, surrounded by an atmos- 

 phere which, in virtue of an excessive heat, extended far beyond 

 the orbits of all the planets, the planets as yet having no existence. 

 The heat gradually diminished, and as the solar atmosphere con- 

 tracted by cooling, the rapidity of its rotation increased by the laws 



