XXII INTRODUCTION. 



around our planet, would have this nebulous matter, in one half of its revolution, with it, and in 

 the other half, against it ; and let the nebulous matter have what tenuity it may, this difference 

 would be perceived in the increased or retarded velocity of the moon ; but no such difference of 

 velocity is ever perceptible. 



6. Our globe, having this matter close about it, would, by its superior attraction, soon draw 

 its particles to itself, and make them a part of its own distinct existence, either as a ring to 

 itself, or in some other way. 



VI. 



The great nebular theory of Laplace, according to which we have, in the formation of globes ; 

 first, an immense body of chaotic, nebulous matter, revolving about its own centre; next, a con- 

 centrated, central portion, producing, or being the sun, with the balance of the nebulous matter 

 formed into a succession of concentric rings, according to the various specific gravities of the 

 matter itself, all still revolving around the sun ; next, these rings broken, and each rolled into 

 a spheroidal mass rotating on its axis, and still also revolving about the sun, and thus giving 

 us the various planets of our solar system ; with a remainder of this ring matter too volatile for 

 such condensation, and still continuing to form a nebulous ring around the sun, giving us, by 

 reflection from its particles, the Zodiacal Light, has been the theory usually adopted to account 

 for this Light, since the publication of the Systeme du Monde. Laplace supposed this rotating 

 ring to lie somewhere between the orbits of Venus and Mars, having, as just remarked, the sun 

 for the centre of its motion. 



Such a ring must be, necessarily, in one of the following cases : 1st, Within the earth's orbit ; 

 2dly, involving the earth; or, 3dly, without the orbit of the earth. 



VII. 



1. It cannot be within the earth's orbit, for the reasons advanced in the V namely, that 

 if so, we could never have the Zodiacal Light, at midnight, on both horizons simultaneously; 

 and could never have it at any great altitude, at any period of the night. 



2. Involving the earth. The objection that if involved in the nebulous matter, we could not 

 get outlines, or have any figure shaped by reflection from its own particles, as stated in the first 

 part of the V, will apply equally to the ring now under consideration. So, also, will objec- 

 tions 4 and 5 of the same ; for, although Laplace supposes that the ring may have a motion 

 equal to that of the earth, or so nearly equal as not to make itself felt in the annual revolution 

 of our globe, yet the moon in each of its revolutions would have to feel the unequally retarding 

 force of this nebulous matter, and would show the effects in every revolution. 



The laws of optics, soon to be noticed in detail, would also apply as an objection to such a ring, 

 with a force that seems to be irresistible. 



VIII. 



A ring beyond the orbit of the earth. For the consideration of this, I have constructed a dia- 

 gram, in the centre of which is the sun ; E, at the intersection of the lines of horizons, is the 

 earth; and the dotted circle is the supposed nebulous ring, at an unknown distance from E, 

 which distance we will suppose to be represented by the unknown quantity x. 



