237 



where it disappeared, and the time, the author of the paper, who 

 had great faith in his friend's exactitude, considered the opportunity 

 favourable for trying what results would be given by the application 

 of Sir J. Lubbock's theory. 



Some dissatisfaction has been felt about theories of shooting-stars, 

 inasmuch as no one of them will explain all the observed phenomena. 

 But though this is undoubtedly a necessary characteristic of a true 

 theory, still great allowances are necessary here where so many dif- 

 ferent classes of cosmical and atmospherical objects may be con- 

 founded even by practised observers ; and where the greater number 

 of observers are utterly unpractised, and their senses wholly unedu- 

 cated for scientific observation. Allowing that some electrical and 

 magnetical effects have been mistaken for shooting-stars, but ex- 

 cluding the baseless electrical, chemical, and lunar hypotheses, a 

 great proportion are undoubtedly of a cosmical nature, and belong 

 properly to astronomy ; and these may be divided into two classes of 

 small bodies. 1st, Those which are circulating round the sun as a 

 primary ; and 2dli/, Those which are revolving round the earth as 

 such. The first we may occasionally see when passing near them in 

 their orbits, but are not likely to come within sight of the same 

 again, unless, indeed, they approach so near the earth as to gravitate 

 towards it instead of the sun, and so become satellites or shooting- 

 stars of the second class. 



Sir J. Lubbock's theory is, that the shooting-stars shine by 

 reflected light, and are extinguished by entering the earth's shadow ; 

 and he has given formulae on this supposition for computing the dis- 

 tance of the body from the spectator by noting the place in the sky 

 where, and the time when, the extinction occurs. 



These formulae have been rendered more convenient for computa- 

 tation by Mr Archibald Smith, Phil. Mag., March 1849 ; and, 

 computed according to them, Captain Jacob's observation gives, for 

 the distance of the body from the observer, 1721 miles ; and that 

 entry into the earth's shadow was the true cause of the disappear- 

 ance, is borne out by the fact that the direction of motion was towards 

 the axis of the earth's shadow. And, on account of the extremely 

 small distance of the body, its change of place during flight would 

 sufficiently account for its gradually appearing in the lower part of 

 the sky when coming out of conjunction, increasing in brilliancy dur- 

 ing its flight (reaching, at its maximum, the brightness of Venus\ and 

 VOL. II. X 



