METEORS AND AEROLITES. 301 



its revolution, under conditions as to time, direction, and 

 physical changes from proximity, which we have not space to 

 detail. The speciilation that this meteoric cloud might be 

 part of the solar nebula known under the name of the 

 Zodiacal Light, was adopted and enlarged upon by Biot, in 

 a memoir read before the Academic des Sciences in 1836. 

 The first exact observer of the zodiacal light, Cassini, had 

 long before inferred that it consists of diffused planetary 

 matter. It is shown by Biot that on the 13th of November 

 the earth is in such relative position that it must necessarily 

 act by attraction or contact upon the material particles of 

 which this nebula is composed, producing phenomena which 

 we may consider to be represented by these meteoric showers. 

 He carries the same theory to the explanation of the sporadic 

 shooting-stars of ordinary nights, by supposing that the 

 constant passage of Mercury and Venus across the more cen- 

 tral regions of this nebula may have dispersed innumerable 

 particles in orbits very little inclined to the ecliptic, and so 

 variously directed that the earth encounters, attracts, and 

 renders them luminous in every part of its revolution. 



Objections have been raised to this theory, and it remains 

 without any fresh confirmation. But under any form that 

 can be given to the question before us, it seems needful to 

 assume for its solution the existence of matter (revolving 

 either in zones or in separate masses and groups) constituting 

 the material of these asteroids. The hypothesis of matter 

 (cosmical matter it has been called) thus arranged ; having 

 periods of revolution more or less regular, and intersecting 

 the orbit of the earth in certain points at certain times, has 

 been adopted by Arago, Herschel, and other eminent astro- 

 nomers; and the conception of a zone or zones of such 

 matter is admitted as best fulfilling on the whole the con- 

 ditions of the problem. Under this view of revolution, 

 already expounded in a more general way as applied to 



