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indicated by him in a paper publifhed in the Tranfadions of 

 the Royal Society, may be changed at pleafure, without difturbing 

 the line of collimation, or altering the quantity of the celeftial 

 fpaces, fubtended by the intervals of the wires j this inflrument, 

 therefore, feems very proper for the purpofe. 



I SHALL fet down the obfervations juft as I inade them, 

 although the firft fet is not cqnclufivc, as they compare magnified 

 areas with lineal apertures. 



The diameter of the objed-glafs is 4-^ inches. I made three 

 diaphragms of pafteboard, with apertures whofe diameters were 

 inverfely proportional to the fquare roots of the magnifying 

 powers ; and by means of thefe I could compare feverally 

 600 and 200, 400 and 200, and 600 and 400 ; although, as 

 remarked above, thefe comparifong arc not exadly juft. 



Things being in readinefs, I began my experiments on De- 

 cember 2d ; and in thefe I did not depend folely on my own 

 eye ; I thought it better to put them to the teft of eyes lefs ufed 

 to aftronomical obfervation, yet fufficientJy acquainted with the 

 pradice, to find fmall ftars in the field of view. 



S BooTis of the fourth magnitude paffed 2H. 12' before the 

 fun : this ftar was vifible with 200, but incomparably better with 

 600 with the diminiflied aperture j it appeared with a planetary 

 roundnefs. This trial was made by me. 



/3 Ursa 



