430 Sujjposcd Connection of Meteoric Phenomena, 



being deemed tiresome, to make out the connection as clearly 

 as possible. 



Note on the Zodiacal Light and on Comets. — The following 

 passages are reprinted from Sir J. Herschel's Treatise on 

 Astronomy (in Lardner's Cabinet Cyclopaedia), to show what 

 his opinions are (art. 626.) : — "It is called the Zodiacal 

 light, and may be seen any very clear evening soon after 

 sunset, about the months of April and May, or at the opposite 

 seasons before sunrise, as a cone or lenticular-shaped light, 

 extending from the horizon obliquely upwards, and following, 

 generally, the course of the ecliptic, or rather that of the sun's 

 equator. The apparent angular distance of its vertex from the 

 sun varies, according to circumstances, from 40° to 90°, and 

 the breadth of its base, perpendicular to its axis, from 8° to 30°. 

 It is extremely faint and ill defined, at least in this climate, 

 though better seen in tropical regions, but cannot be mistaken 

 for any atmospheric meteor or aurora borealis. It is mani- 

 festly in the nature of a thin lenticularly-formed atmosphere, 

 surrounding the sun, and extending at least beyond the orbit 

 of Mercury, and even of Venus, and may be conjectured to be 

 no other than the denser part of that medium, which, as we have 

 reason to believe, resists the motion of comets ; loaded, perhaps, 

 with the actual materials of the tails of millions of those 

 bodies, of which they have been stripped in their successive 

 perihelion passages (487.), and which may be slowly subsiding 

 into the sun." (Lardner's Cyclopaedia, xliii. 407 — 8.) 



"(Art.487.) The tail of the great comet of 1680, immediately 

 after its perihelion passage, was found by Newton to have been 

 no less than 20,000,000 of leagues in length, and to have 

 occupied only two days in its emission from the comet's body ! 

 a decisive proof this of its being dashed forth by some active 

 force, the origin of which, to judge from the direction of the 

 tail, must be sought in the sun itself. Its greatest length 

 amounted to 41,000,000 leagues, a length much exceeding 

 the whole interval between the sun and earth. The tail of the 

 comet of 1769 extended 16,000,000 leagues, and that of the 

 great comet of 1811, 36,000,000. The portion of the head 

 of this last comprised within the transparent atmospheric 

 envelope which separated it from the tail was 180,000 leagues 

 in diameter. It is hardly conceivable that matter once projected 

 to such enormous distances should ever be collected, again by the 

 feeble attraction of such a body as a comet, — a consideration 

 which accounts for the rapid progressive diminution of the tails 

 of such as have been frequently observed" (Lardner's Cyclo- 

 paedia, xliii. 311.) 



Now it is evident, that, if Sir J. Herschel be correct in his 



