Life of the Dvlic de Chaulnes. 265 



astonished, in reading this work, at the resources with which 

 his genius furnished him, and the sagacity with which he 

 profited by an influity of circumstances, that prubaoly would 

 iiave escaped other persons. The fruit of so nuich labour 

 and attention wa? the production of an inslruasent eleven 

 inches radius furnished with achromatic telescope-, the ac- 

 curacy of which was so great, that, when compared with 

 two excellent quadrants of six feet radius in measuring sol- 

 stitial meridian altitudes of the Sun and Arctunis, the same 

 precision was obtained as with them. This trial was the 

 strongesi and mof-t ceitain proof of its excellence to wluvjh 

 it could have been submitted. 



Not only did he give his instrument the degree of ac- 

 curacy which we have just spoken of, but he also con- 

 trived means of rendering all others equally as exact that 

 might hereafter be made, by a Iarg€ platform, which \\ft pro- 

 posed to construct on this principle, and which was, if we 

 may use the expression, to serve in future instead ot an 

 able artist. We leave men of science to judge wheiher the 

 duke de Chaulnes has not completely resolved this difficult 

 problem, and likewise to appreciate the degree of gratitude 

 due to him for this discovery, so valuable to all the mathe- 

 matical and astronomical worW. This entirely new art, the 

 principles of which he had given, as before observed, in 

 1763, have since been published in greater detail in 176S, 

 in the description of the arts published by the acadeniy. 



Every thing that the duke de Chaulnes did with regard to 

 the construction of astronomical instruments, proved to 

 him the great utility of achromatic telescopes. This was a 

 sufficient inducement for bin) to endeavour to improve them, 

 and he gave the public a Memoir, in which he details his 

 ideas on the subject. 



We are astonished, in reading this work, at the inventive 

 powers of his genius, in contriving niethods for determining 

 quantities, which, to superficial ol)servers, appear not 

 worthy of notice, 'i'lie same microscopis which before 

 served for dividing his instruments arc here again found 

 useful, but cnqiloyed in a very different manner, and 



inoLuUed 



