252 Some Account of the late M, Guinand. 



doubt that, in operating on a greater scale, he might easily be 

 able to obtain one of a diameter double or triple the extent of 

 those last mentioned, he justly concludes tliat his process has at 

 length removed the obstacle whicli the non-homogeneity of flint- 

 glass opposed to the construction of large achromatic object- 

 glasses *. 



When M. Guinand first obtained blocks including portions of 

 good glass, his practice was to separate them, by sawing the 

 blocks into sections that were horizontal, or perpendicular to their 

 axis ; then, polishing the sections, he selected the portions adapted 

 to his purpose, and returned the others to the crucible ; but, in- 

 dependently of the tediousness of the labour, and the waste occa- 

 sioned by sawing, this process was attended with the great disad- 

 vantage of not cutting the finest parts of his glass in the manner 

 best calculated to obtain disks as large as possible ; for frequently 

 the most homogeneous parts were thus divided ; but a fortunate 

 accident, of which he availed himself with his usual adroitness, 

 conducted him to a process more simple and better suited to the 

 attainment of his object. 



One day, while his men were carrying a block of this glass on 



mogeneous glass. This disk had been put into the oven for the last time, to 

 be gradually cooled ; and the operation being now considered as completed, 

 the friends were, as usual, admitted ,• in the midst of the congratulations 

 offered, on this unprecedented success, after an unusually long seclusion, the 

 fire, by some accident or neglect, caught the roof of the building. On this 

 alarming occasion all present exerted themselves, and after some trouble the 

 flames were extinguished ,• but not before some water had found its way into 

 the oven, and destroyed its precious contents. The discouragement caused by 

 this misfortune, and some other circumstances, ever after prevented M. Gui- 

 nand from attempting any new experiment on a similar scale. 



* " At the Exposition of the French Industry, several large telescopes 

 were exhibited by MM. Lerebours and Cauchoix, constructed with flint-glass, 

 made by M. Guinand, of Neufchatel. One made by Lerebours had its object- 

 glass nine inches in diameter, French measure, and its focal length ten and a 

 half feet -, and another by Cauchoix, had the diameter of the object-glass 

 eleven inches, and the focal length eighteen feet." — See the Edinburgh Philo- 

 sophical Jownal, No. XX. for April, 1824. — See also Sc. et Arts. Nouv. S^rie, 

 Vol. XXV. No. 2. Feb. 1824. 



