^74 0'^ i^' Quejl'ton, whetheY the Sun, Moon, and 



of the moon having an atmofphere. Some fufpicion is ex- 

 cited in regard to the accuracy of this obfcrvation, becaufe 

 many aftronomers, during the fame celcftial occurrences at 

 other times, have never obferved the fmalleft change of 

 figure in the ftars either during their ingrefs or egrefs. De 

 la Hire *, however, obferved, during an occuhation of Ju- 

 piter by the moon, that when Jupiter was at the diftance of 

 13' from the moon, he fliowed the fame lively colours as 

 when he approached nearer. But, to make thefe colours - 

 appear, it was neceffary that Jupiter fnould be at the edge of 

 the aperture of the telefcope ; for when he was in the middle 

 of it none were feeu. From this circumltance he naturally 

 concludes, that the colours did not proceed from the moon, 

 but from the glafles of the telefcope, which, as they are 

 convex, form at their edges a fort of circular prifm. Venus, 

 which appeared foon after, exhibited the fame colours as 

 Jupiter. T. Mayer, therefore, gives this excellent rule : 

 Make the experiment without prejudice, and take care to ufe 

 the telefcope with the necefl'ary precaution : it will then, 

 perhaps, be found, that the planets and fixed ftars approach 

 the moon at all times in their proper form. De I'lfle afcribed 

 this phenomenon to the inflexion of the rays alone f. 



We now come to the third argument adduced in favour of 

 the lunar atmofphere, or the tremulous motion of the fun's 

 limb before he touches the moon during a folar eclipfe. This 

 undoubtedly arifes from our atmofphere alone ; and we have 

 fo many inllauces of fuch quivering on other occafions, that 

 I do not think it neceffary to fav any thing farther rcfpeftino- 

 it. -This is certainly one of the weakeft proofs advanced in 

 favour of a lunar atmofphere. 



In regard to the fourth proof, that the diameter of the 

 moon at the commencement and end of eclipfes has been 

 obferved to be fmaller, and at the time of the greateft dark- 

 nefs to be greater, it appears to be almoft void of foundation j 

 and indeed we have more inftances of fuch a phenomenon not 

 being feen, than of its being obferved. During the total 



* Memoires de I'Acad. de Paris 1715, p. 14S. 



f Mem. pour fervir a I'Hifloire et au Piogrcs dc rAftronomie, Paris 

 173S, p. 249. 



folar 



