98 



were connected with ff the same emanations, 

 which render the appearance of spots and facute 

 periodical on the solar disk." But this excellent 

 observer does not mention those changes of 

 intensity in the zodiacal light, which I have 

 several times remarked between the tropics, in 

 the space of a few r minutes. Mairan * asserts, 

 that in France it is common enough to see the 

 zodiacal light, in the months of February and 

 March, mingling with a kind of Aurora Borealis, 

 which he calls undecided, and the nebulous 

 matter of which spreads itself all around the 

 horizon, or appears toward the West. I very 

 much doubt, that, in the observations I have 

 been relating, there was any mixture of these 

 two species of light. The variations in intensity 

 took place at considerable altitudes ; the light 

 was white, and not coloured ; tranquil, and not 

 undulating. Besides, the Aurora Borealis is so 

 seldom visible between the tropics, that, during 

 five years, though almost constantly sleeping in 

 the open air, and observing with unremitting 

 attention the vault of Heaven, I never perceived 

 the least traces of this phenomenon. 



Resuming the whole of what I find noted on 

 iny registers concerning the variations of the 

 zodiacal light, I am rather inclined to think, 



* Traits de VAurorc Boreale, (2d ed.) p. 112—166. 

 Mim de VAcademie, 1733, p. 482, id. 1734, p 572. 



