Mr. J. P. Joule on Shooting Stars. 349 



that there was no more occasion to notice explicitly the light 

 coming from the wires, than there would have been if the 

 earth had really been at rest. While, however, I would vin- 

 dicate my explanation from any flaw or deficiency of reasoning 

 (unless the not noticing formally and explicitly the light coming 

 from the wires be regarded as such), I allow that, without 

 investigation, I fancied the path of a ray in space tO-be curvi- 

 linear. It was first virtually proved by Professor Challis, 

 though not explicitly stated, that the path was rectilinear 

 throughout. Consequently the angle/'6'5'(Phil. Mag.,vol.xxvii. 

 p. 14), which I argued was insensible, is in fact zero. The 

 method which consists in considering the rectilinear propa- 

 gation of light as resulting from the supposition that 2idx+ ... 

 is an exact differential, and then the law of aberration as 

 resulting from the rectilinear propagation, instead of consider- 

 ing the whole at once, has the advantage of showing that we 

 are at liberty to suppose the velocity of the aether at the sur- 

 face of the earth to be of any amount relatively to the surface. 

 1 iiad not contemplated this case ; for it was the precise ob- 

 ject of my investigation to get rid of the apparent necessity of 

 supposing the rether to be rushing through the air and through 

 the earth itself as the earth moves round the sun. 



XLVIII. On Shooting Stars. Bt/ J. P. Joule, Correspo?idi?ig 

 Member of the Royal Academy of Sciences, Turin, Secretary 

 to the Literary and Philosophical Society, Manchester^'. 



I HAVE read with much interest the valuable papers on 

 shooting stars inserted by Sir .T. W. Lubbock in the 

 Numbers of the Philosophical Magazine for February and • 

 March. This philosopher seems to have placed the subject 

 in a fair way for satisfactory solution. He has advanced three 

 hypotheses to account for the sudden disappearance of these 

 bodies, the last of which he has enabled us to prove or dis- 

 prove by actual observation. 



I have for a long time entertained an hypothesis with respect 

 to shooting stars, similar to that advocateil by Chladni to ac- 

 count for meteoric stones, and have reckoned the igiiition oi 

 these miniature planetary bodies by their violent collision with 

 our atmosphere, to be a remarkable illustration of the doctrine 

 of the equivalency of heat to mechanical power or vis viva. In' 

 a popular lecture delivered in Manchester on the 28th of April 

 1847, I said, " You have, no doubt, frequenUy observed what 

 are called shooting stars, as they appear to emerge from the 



* Communicated by the Author. 



