CERTAIN HARMONIES OP THE SOLAR SYSTEM. 51 



orbit of Mercury, and, consequently, it does not produce the zodiacal light, which 

 seems to extend even beyond the earth's orbit. Moreover this atmosphere, whose 

 polar axis must be at least two-thirds of that of the equator, is very far from 

 having the lenticular form which observations give to the zodiacal light. "^ 



(71) Next as to the origin and the constitution of the material which gives us 

 the zodiacal light, we have: "If, among the zones abandoned by the atmosphere 

 of the sun, there should be molecules too volatile either to combine themselves, or 

 to unite with the planets, they ought, while continuing to circulate about the sun, to 

 present all the phenomena of the zodiacal light without opposing a sensible resist- 

 ance to the diverse bodies of the planetary system, either because of the extreme 

 rarity of those volatile molecules, or because their motion is very nearly the same 

 with that of the planets which they encounter."^ 



It will be observed that the first of the two quotations, here made, intimates it as 

 probable that the material from which the Zodiacal Light proceeds, itself extends 

 beyond the earth's orbit. This is, in fact, intimated by the existence of what in 

 Crerman accounts of observations of the Zodiacal Light has been designated as the 

 gegenschein ; which is seen in the part of the heavens opposite to the sun; the 

 existence of which phenomenon is established by numerous observations, such 

 especially as are detailed in various numbers of the Asironomische Naclirichten. 



(72) Both eastern and western appearances occurring simultaneously are reported 

 by the late Rev. George Jones, A.M., chaplain in theU. S. Navy; these phenomena 

 being, among numerous others, the description of which, and other things connected 

 with them, itself occupies the whole of vol. iii. of the Report of the U. S. Japan 

 Expedition ; and the extent of the light to hotli sides of the heavens is confirmed 

 by the observations of Col. Charles G. Forshey, U. S. A., made while he was stationed 

 in an elevated and dry region of Texas; where, as stated by Col. Forshey to the 

 author of this paper, that phase of the phenomenon was a common occurrence ; 

 though the appearance of the Zodiacal Light in lower Louisiana, as described by 

 him, was very different.® 



(73) All this makes it more difficult to admit that the material in question can 

 be maintained in position, with the sun for its centre of reference ; the conservative 



' Systeme du Monde, Book IV, Chap. X. ^ Sysleme du Monde, Note VII. 



^ In Col. Forshey's manuscript notes, which he has since confided to me, the Zodiacal Light is 

 described as being "very distinct across the heavens," Nov. 10, 1858, at 10 o'clock P.M. As 

 delineated on star charts, the outlines on this occasion, as on many others, approach to a hyperbolic 

 form, the central line of the luminous band being in the position of an asymptote to the two edges; 

 or — if the comparison may be allowed — the appearance often was that of an enormous trumpet, the 

 lower end widening rapidly and extensively; and on the occasion here referred to, tivo such appear- 

 ances are delineated, as having been observed ; the broad ends spreading out to the horizon, on 

 opposite sides, and the narrow portions united midway. 



On the 9th of May, 1860, the phenomenon is described as being "faintly visible across the canopy;" 

 though the whole display is characterized as being "rather faint;" while the "evening" is noted as 

 being "splendidly clear." 



Also Nov 13, 1859 — "Not a very bright display. Still column yery distinct all the way across 

 the sky." 



And, in a "Note" under the date of March 31, 1858, Col. Forshey expressly says: "I now begin 

 to think that well-trained eyes can see it all the way round, at all times that are clear and moonless." 



