250 Chronicles of Science. [April, 



the moon on the corona would indicate that the glory of light 

 comes from a region beyond the moon. 



Professor Tait has put forward a theory respecting comets' tails 

 which deserves mention, though it can hardly he accepted as ex- 

 planatory of even the more ordinary cometic phenomena, still less 

 of the abnormal phenomena which many comets have presented. 

 He considers that the visibility of a comet's tail may depend on 

 the position of the earth with respect to the plane in which the 

 meteoric components of the tail are travelling. When the lines of 

 sight from the earth are directed at a considerable angle to this 

 plane, the tail would scarcely be visible at all ; but when the earth 

 moves into any plane touching the surface in which the meteoric 

 particles are for the moment mainly gathered, the tail becomes 

 visible at once along its entire length, " just as a distant flock of 

 sea-birds comes suddenly into view as a dark line when the eye 

 is brought by their evolutions into the plane in which they fly." 

 Professor Tait does not show that the appearance of any comet's 

 tail has corresponded to the earth's assuming such a position as 

 he describes ; and there is a further objection to his theory in the 

 fact that the tails of many comets have been visible for months at 

 a time, whereas the earth cannot have been so long in the plane of 

 meteoric aggregation unless that plane coincided with the ecliptic, 

 which has not been the case in any known instance. 



Dr. Balfour Stewart has brought before the Astronomical Society 

 certain views respecting the " Aurora," which belong more properly 

 to the Chronicle of Physics than to that of Astronomy. But a sug- 

 gestion thrown out in that paper as to the nature of the Zodiacal 

 Light must not be left unnoticed here. He asks whether this 

 Light may not be a terrestrial phenomenon — as Mr. Lockyer has 

 suggested. "When once the anti-trades have reached the upper 

 regions of the atmosphere, they will become conductors from their 

 tenuity; and as they pass rapidly over the lines of the earth's mag- 

 netic force we may expect them to be the vehicles of an electric 

 current, and possibly to be lit up as attenuated gases are when they 

 conduct electricity. May not these form the Zodiacal Light ? " 

 The answer to this question cannot but be negative. A pheno- 

 menon which rises and sets, which occupies in all latitudes a defi- 

 nite relation to the fixed stars— in respect of position, cannot by 

 any possibility be a terrestrial one. The region of the counter- 

 trades may perhaps be lit up as Dr. Stewart suggests ; if so the 

 whole sky would show the light, and we have here perhaps a satis- 

 factory explanation of the phosphorescent light often visible over 

 the whole heavens at night. But the counter-trades cannot throw 

 a tongue of light over a definite region of the celestial sphere, nor 

 can they regularly set on spring evenings and as regularly rise on 

 autumn mornings. 



