52 STATEMENTANDEXPOSITIONOF 



influence of the great planets being not supposable within tlie extended limits of 

 the solar system; tiiough the satellites of Saturn, [^Note ^ to 7 of (43)], are efficient 

 in that way, maintaining the position of the rings, under the 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 jjortion of the material in question, 

 which Qught, unless uncommonly extensive, to be seen under a smaller angle than 

 the other portions of the same; a difficulty to which the hypothesis recently 

 advanced by Mr. Richard A. 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 consider- 

 able degree of flatness in the actual figure of the zodiacal disk, and more especially 

 of its more distant portions."^ 



And just that difficulty still remains if we were even to admit Prof. Arthur W. 

 Wright's conclusion from his recent experiments on the polarization of the Zodia- 

 cal Light, as far as this — that "the light is reflected from matter in a solid state ^ 

 since, he adds, in explanation of the same that this solid matter is that of " innu- 

 merable small bodies revolving about the sun in orbits of which more lie in the 

 neighborhood of the plane of the ecliptic than near any other plane passing through 

 the sun."^ 



Now this portion of tlie hypothesis of Prof. Wright, Mr. Proctor, and, it may 

 be, others — whatever may be the special composition of the material in question — 

 would seem to require that the apparent form of the Zodiacal Light should be some- 

 what like that of the head of a comet, with the expansion beyond it extending 

 upward from the sun; whereas the actual appearance and position are both the 

 reverse of that ; the hroad base near the horizon, and the narroio and curved 

 termination at the upper end. 



And then, moreover, it would seem, on the part of the hypothesis here consid- 

 ered, that, in any event, there must be a conspicuous central beam or core of the 

 Zodiacal Light; which we do not find. 



And, lastly, what shall be said of the planetary perturbations, which, it would 

 seem, ought to be superinduced by such a closely arranged group of meteors; 

 especially if the "light" be indeed "reflected from matter in a solid state f 



Other objections to hypotheses which would make the material 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 Chaplain Jones in the 

 volume already referred to. The hypothesis that the Zodiacal Light is due to 



• 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. 11, 1870). 



' American Journal of Science and Arts, Third Series, vol. vii. p. 457 (No. 41— May, 1874). 

 Will, after all, our terrestrial experience as to the conditions of polarization, justify us in making it 

 a criterion of the state of anything so peculiar as the matter in question ? 



