269 Some Account of the late M. Guinand, 



factures the flint and crown-glass which he uses in their con- 

 struction, after having made with his own hands his vitrifying 

 furnace and his crucibles, who, without any mathematical know- 

 ledge, devises a graphic method of ascertaining the proportion of 

 the curves that must be given to the lenses, afterwards works and 

 polishes them by means peculiar to himself, and lastly, constructs 

 all the parts of the different mountings either with joints, or on 

 stands, melts and turns the plates, solders the tubes, prepares 

 the wood, and compounds the varnish. 



[Here follows a long and detailed explanation of the original 

 process pursued by M. Guinand for giving the required curve to 

 his lenses ; but as the mode adopted in this country appears to be 

 superior, that detail is omitted.] 



In beholding M. Guinand in his seventy-sixth year, assailed 

 with the infirmities incident to his multifarious labours and his 

 advanced age, infirmities which have latterly been so severe as to 

 disable him from all exertion, it is to be regretted that such a 

 man cannot enter upon a new career ; it is to be lamented that, 

 after liaving sacrificed to his art so much more than could have 

 been expected from a man in his circumstances, he should derive 

 from them so little advantage ; and lastly, it is painful to think, 

 that this man, in attaching so little importance to the honour of 

 his discovery, should not have made it more extensively known, 

 and connected it more closely with his name ; since it is a disco- 

 very which, by the perfection it imparts to telescopes, opens the 

 way to very important acquisitions in the vast field which the 

 heavens still oiFer to optical instruments in a state of perfection. 



E. R. 



Dsited Neufchdtel, Ja7i. 1824. 



Art XII. Theorems in the Doctrine of AatJuxTiEs* By a 

 Correspondent. 



Whatever may be the difficulties in estimating the rate of in- 

 terest for small portions of the year, which have perplexed many of 

 the most popular authors on annuities payable at short intervals of 



