190 Mr. G. J. Stoney on the Connexion 



The discovery of tlic Master of the Mint becomes now of ex- 

 ceeding interest, since it seems to show, first, that hydrogen is 

 one of the constituents of comets; secondly, that the meteoric 

 bodies he examined, when they originally joined their comet, 

 fell in with a velocity sufficient to raise them by the friction 

 they suffered to a red heat; thirdly, that the density of the 

 comet was sufficient to occasion in front of the advancing me- 

 teorite a pressure of several atmospheres ; fourthly, that when 

 the meteors and the comet afterwards parted company, they 

 glided asunder so quietly that the meteors were not again raised 

 to any very high temperature; aud, finally, that the friction 

 they again encountered in passing through the earth's atmo- 

 sphere was not sufficiently protracted to raise their internal parts 

 to a red heat. 



When the cluster of November meteors passed the planet 

 which diverted them into the solar system, they were unequally 

 acted on by it, the path of those which lay nearest being most 

 bent. To this, as M. Leverrier has remarked, is to be referred 

 their subsequently moving in slightly differing orbits with slightly 

 different periodic times round the sun — which after the lapse of 

 many revolutions has gradually extended them along their nearly 

 common path, and will as time goes on still further lengthen 

 out the stream. Hence the feeble gravity of the comet was not 

 sufficient to restrain the meteors which were originally within it 

 from yielding to these weak forces. The gravity of the comet 

 accordingly cannot have been what kept the parts of its own 

 mass from giving way to the same influences, and being (like 

 the meteors) drawn out into a long thread. This is one of seve- 

 ral considerations* which all point to the same conclusion — that 

 a comet does not consist of matter merely held together by the 

 mutual gravity of its various parts, but also coheres in virtue of 

 some more powerful forces, perhaps not unlike those molecular 

 forces which keep together the parts of a solid body. 



It is remarkable that the principal meteoric streams which 

 at the present day cross the earth's path have a retrograde 

 movement, although the motion of most of the comets that are 

 known to be periodic is direct. Perhaps this is to be accounted 

 for by the earth's having exercised a more intense scattering in- 



accelerate the comet at the expense of some of the vis viva of the meteors 

 which pass through it, and finally, when the motion of the comet has been 

 brought sufficiently into accordance with that of the meteors, to cause a 

 gradual accumulation at the centre of the comet of those meteors which 

 then happen to lie within the space occupied by it. 



* Other groirads for this belief will be found in a Memoir on the Phy- 

 sical Constitution of the Sun and Stars, lately submitted to the Royal 

 Society. 



