138 M. HE Zach's jyirotiomkal Obfervatkns. 



large telefcopes, which magnify too much, and give too great a 

 tranfit between the penumbra and the true dark (hadow. On 

 that account fome celebrated aftronomers advife to ufe for the 

 echpfes of the moon no greater telefcopes than of four or five 

 feet length. It was remarked at Paris, that in an eclipfe of 

 tlie moon, obferved through a telefcope of DoLLOND,the focus 

 of its object lens being 30 inches, and likewife through a tele- 

 fcope of five feet length ; the eclipfe appeared to begin 4'' ^^ 

 fooner, and to end 4^ 7^' later, through the fmall than 

 through the long telefcope ; the like has been remarked by 

 feveral others, and it has been alfo obferved by myfelf. As to 

 my obfervations I am tolerably fatisfied with them, as they do not 

 differ materially from thofe of Father le Fevre, though' it is 

 known that in eclipfes of the moon no greater exa61:nefs than 

 that of a minute can be obtained. The m^oon's fpots were 

 carefully obferved ; for it is known, that the mean of the ob- 

 fervations of the moon's fpots is fufficient to afcertain the 

 longitude of a place to 4^^ or 5'^ nearly. M. de la Lande 

 comparing the obfervations of the moon's fpots in an eclipfe, 

 made the 22d of November, 1760, in Vienna, by the Impe- 

 rial Aftronomer Abbe Hell, with thofe made at the fame 

 tim^e in Paris by M. Messier, finds the difference of meri- 

 dians to be 56^ 13^^, which agrees very exa(ftly with that afcer- 

 tain^d by other means. 



Correfpondent 



