11 APPENDIX. 



the observations of Col., now Prof. C. G. Forshey, made while 

 he was stationed in an elevated and dry region of Texas, where, 

 as stated by Prof. Forshey to the author of this paper, the phe- 

 nomenon was a common occurrence ; the appearance of the zo- 

 diacal light in lower Louisiana is very different. 



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 influence of the great planets being 

 not supposable within the e.xtended limits of the solar system ; 

 though the satellites of Saturn are efficient in that way, main- 

 taining the position of the rings under ihe more stringent con- 

 ditions of a closer arrangement. 



Added to this is the consideration of the enormous extent which 

 would seem to be required on both sides of the ecliptic, to account 

 for' the great breadth of the base of the zodiacal illumination, 

 even after the disappearance of twilight in the evening, or before 

 daylight in the morning ; all which seems to be true of the more 

 dense, and, if surrounding the sun, also the more distant portion 

 of the material in question, which ought, unless uncommonly ex- 

 tensive, to be seen under a smaller angle than the other portions 

 of the same ; a difficulty to which the hypothesis recently ad- 

 vanced by Mr. Richard Proctor, F.R.A.S., viz., that the zodiacal 

 light is due to a closely arranged group of meteors, would seem 

 to be especially liable; and all the more so if, "assuming" (as he 

 himself says " we are bound to do") a considerable degree of 

 flatness in the actual figure of the zodiacal disk, and more espe- 

 cially "of its more distant positions."* And just that difficulty 

 still remains ; if we even so far admit Prof Arthur W. Wright's 

 conclusion from his experiments on the polarization of the Zodi- 

 acal Light, viz. : "that the light is reflected from matter in a solid 

 state.", .-t 



Other objections to the hypothesis which would make the ma- 

 terial to which we owe the zodiacal light to be an appendage of 

 a lenticular or other form referable to the sun as its centre, are 

 very exhaustively considered by Rev. Mr. Jones in the volume 

 already referred to. 



The hypothesis that the zodiacal light is due to reflection from 

 the earth's atmosphere, is also discussed and rejected by him. 

 Upon this, however, it will not be necessary here to comment ; 

 as it, most probably, is no longer insisted upon by any one. 



It remains then to consider, with ivhat 'modifications we may 

 admit Mr. Jones's hypothesis: That the nebulous material which 

 gives the zodiacal light, is a terrestrial appendage; and also what 

 is the conservative force which may insure its preservation of 



* In a long and carefully considered "Note on the Zodiacal Light" in 

 the Monthly Notices of the Royal Astronomical Society, vol. XXXI, No. 

 1 (Nov. II, 1870). 



t American Journal of Science, &c., Third Series, Vol. VII, No. 41. 



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