OF ARTS AND SCIENCES. 183 



X. 



THE MOON'S ZODIACAL LIGHT. 

 ByL. Trouvelot. 



Presented Nov. 14, 18T7. 



During the evening of April 3, 1874, the "zodiacal light" was 

 particularly brilliant ; especially close to the horizon, wliere it appeared 

 as a segment of a circle, having an irregular wavy outline, giving it a 

 vague resemblance to the beams of a faint aurora. Although the sky 

 was clear, it was found impossible to observe with the telescope on that 

 night, on account of the great disturbance of the atmosphere. At d^ 

 45™, the declination needle indicated a very strong magnetic perturba- 

 tion in Cambridge, oscillating through an angle of 3" 22'. How- 

 ever, no aurora was visible at this time, although the phenomena 

 usually attending them were manifested during the evening by the 

 tremulous appearance of the telescopic images. 



While going home, I remarked in the East a strange conical light 

 rising obliquely from the top of the roof of a building, behind which 

 the moon, then about 15° or 20° above the horizon, was concealed 

 from view. By going away from the building, the conical light, which 

 closely resembled the tail of a comet, became brighter and brighter as 

 it approached the moon, upon the western limb of which it rested. 

 The base was at least as wide as the diameter of the moon ; but it ex- 

 tended beyond, on each side, by a fainter light, which gradually van- 

 ished in the sky. The extension of this luminous appendage I 

 estimated to be equal to eight or ten times the moon's diameter. It 

 was not readily visible when the moon was in sight, as the brilliant 

 light of our satellite overpowered its dim brilliancy. The axis of this 

 appendage was found to be coincident, or nearly so, with the ecliptic ; 

 and its line prolonged in the west passed a little to the north of 

 Jupiter. 



The phenomenon had been observed for about fifteen minutes, when 

 it gradually faded away until it almost totally disappeared five min- 



