Mechanical Philosophy. 53 



the hints and pubhcations of the celebrated Eui er 

 on this subject, though found erroneous, probably 

 contributed something to Mr. Dolland's disco- 

 very; and that the distinguished mathematicians 

 Clairaut and D Alemeer r, about the same time' 

 rendered themselves very conspicuous among the 

 philosophers of Europe, by their ingenious calcu- 

 lations and suggestions, in aid of the achromatic 



instrument. 



^"V ^'■P'" t^e necessary imperfection, and the 

 small limits to which the dioptric plan of mJnt 

 fymg distant objects is confined, the improvem^'ent 

 of the Reflecting Telescope became, early in the 

 century, an object of particular attention This 

 instrument, which had been invented, in the ore 

 ceding century, by Mr. James Gregory,^ of 

 Aberdeen and which had been executed, on a 

 different plan, by Sir Isaac Newton, was greatly 

 improved by Mr. Hadley, who, in 17 19 nre 

 sented a very powerful Telescope of this k/nd to 

 the Royal Society. In 1734 Mr. Short, an in<.e- 

 nious artist of Edinburgh, devised still further im 

 provenients in this instrument. These were chiefly 

 eliected by a new method which he discovered of 

 grinding mirrors. But the secret art which en 

 abled h.m to do this with so much success, is said 

 to have died with him. After him, Mr. Mudge 

 o London, by making specula of a composition of 

 difl^erent metals, and by inventing a method o f 

 grinding them in the parabolic curve, which had 

 been considered so difficult a problem by his 

 predecessors, efl^-ected yet greater improvements. 

 Mr. Mudge was followed by his countryman Mr 

 tDWARDs, who also laboured, with considerable 

 success, on the same instrument. But it was re 

 served tor the great Astronomer Herschel, to fur- 

 nish .he world with reflecting telescopes of the 



