Life of John Bevls, M.D. F.R.S. m. 23i 



■of telescopes, by using a compound object glass, composed 

 of a convex lens of crown class and another concave one of 

 white flint glass; or else, by means of two convex ones of 

 crown glass, and one concave one between them of white 

 flint glass. Dr. Bevis was the first who gave the name" of 

 achromatic to telescopes made in this manner, which name 

 has ever smce been universally adopted both at home and 

 abroad. This invention induced him to make some curious 

 experiments on the refractive power of glass, in the com- 

 position of which he had used a quantity of borax, and 

 found the rcfrangibility was about as great as that of Eng- 

 lish crystal. 



The French astronomers had always received the credit 

 of bemg the first inventors of the wire micrometer, uniil 

 Dr, Bevis, in looking over some letters, the originals of 

 which were in lord Slacclesfield's library, found, by acci- 

 <lent, that Gascoigne first invented it in the year 1641, 

 whereas Auzout's letter to Mr. Oldenburg, which only 

 mentions his having jised it to measin-e the sun's diameter, 

 was not dated till the 28th of December 1666. 



M. Grischou, when he was at Lcyden in 1749, engaged 

 M. Schullens, professor of Arabic in thatoity, to translate 

 the manuscript, in the public library of that city, containing 

 the observations of Ibn lunis, made at Jafla, about six or 

 seven miles from Cairo, in Egypt, in the years 977, 978, 

 and 979, where are recorded, among other things, two re- 

 markable eclipses of the sun. Dr. Bevis procured a copy 

 of this manuscr!{)t in order to compare modern observations 

 with these antient ones, for the purpose of settling the 

 maximum of some equations in the solar tables ; but in th.e 

 course of bis researches he found ihem so obscure and un- 

 satisfactory that he was obliged to reject them. He afler- 

 wardd presented this manuscript to M. de ITsle, and it has 

 lately been translated into French bv iSi. Caussm, and in- 

 serted in the Mem. de I' Iiistit. Nat, torn, ii.*' 



At the death of Mr. Bliss, in 17fi3, his friends made 

 great exertions to procure for him the situation of astro- 

 nomer royal ; but Dr. Maskclvne obtained it thiough the 

 interest of the earl of Maeeleslicld, who wa.j at liiat time 

 president of the Royal Society. His majesty, notwith- 

 standing he could not comply with his wishes in this in- 

 eiance, was very partial to him, and requested his assisl- 



• An analysis nf this curious and vabnbtc :iianusril[it raay be seen in the 

 first volume of Dr. Garnctt's Ann;iK of Philo opbv, p. 105. l.;i Place hai 

 di;n>-cd great bcnclit trofii t'lf u-e of it. 



ancc 



