smaller than the orbit of Venus, and indefinitely diffused along the equatorial plane. Notwithstanding its dim indefiniteness, neither the spectroscope nor the camera is wholly ineffective for the scrutiny of this extraordinary appurtenance. We have learned positively that its radiance is of the continuous sort, the origin of which through the reflection of sunlight from small solid bodies seems more than probable. The whole structure must accordingly be of a pulverulent or meteoric nature; it consists of independently moving particles. But to the further question, Under what regimen do these particles circulate? no decisive answer is as yet forthcoming. M. Hansky[116] and others hold the light to be a true solar appendage, an extension of the corona, in which case it would have a formal, but no material permanence. It would represent the continually changing aggregate of multitudinous minute bodies issuing from or repelled by the sun, and in large proportion falling back towards his surface. Yet some difficulty is raised to this view by the vast dimensions of the problematical glow. That it extends far beyond the earth's orbit is rendered patent by the phenomena of the Gegenschein and the band. True, the scope of the sun's repulsive action cannot be limited; still, we might naturally expect its products to become too attenuated for recognition beyond a radius of perhaps fifty million miles. Admitting, on the other hand, the residual character of the zodiacal light, we should attribute to it a constitution analogous to that of Saturn's rings. Each one of the cosmic atoms collected in it would revolve round the sun on its own account, scarcely disturbed by its neighbours. Nor need we despair of determining with reasonable certainty which way the truth lies in this matter. The rival hypotheses may be tried by a criterion the application of which is by no means remotely feasible. It is furnished by the geometrical relations of the zodiacal light. Evidently, if the sun can claim organic connection with it, its axis should coincide with the plane of the solar equator; while, if it represent wastage from the Kantian nebula, it should stretch along the principal plane of our system--the plane of maximum moment of momentum--the plane towards which the primitive agglomeration of revolving particles collapsed as it condensed. The question of planes is, then, crucial. Is the zodiacal effluence placed symmetrically as regards the solar equator, or does it appertain properly to the ecliptic, which deviates very slightly from the fundamental plane of the solar system? The evidence is, unfortunately, contradictory. Most observers have located the dim equinoctial cone right along the pathway of the sun; some, under exceptionally favourable circumstances, have perceived in it a marked departure from the track of the Signs.