Paper on Aplanutk Object-Glasses. 231 



first plano-convex achromatic with two glasses united, of a 

 short focus, thin, and of a small diameter. (See Remark L.) 

 This lens had a focus of four lines, a diameter of two lines, and 

 a thickness of one line at the centre, and it was with lenses of 

 this kind that the improved microscope was constructed which 

 was presented to the Societe d 'Encouragement on the 30th 

 March 1825. On this occasion the reporter, M. Hachette, re- 

 marked : " The images seen through this microscope are free 

 from every sensible aberration, either of sphericity or refran- 

 gibility : objects, whether opaque or transparent, appear in it 

 with a distinctness equal to that of achromatic telescopes. 



The first achromatic object-glass which had been made in 

 England was the triple object-glass of nine-tenths of an inch 

 focus, executed in 1824 and 1825 by Mr Tulley, at the desire 

 of Dr Goring, (See Remark M,) and of which an account was 

 published in different scientific journals. Mr Tulley after- 

 wards greatly improved his first work, and Mr Dollond was 

 also occupied with this part of dioptrics. With respect to Dr 

 Goring, he has, by means of his learned memoirs, done a ser- 

 vice to the opticians of every country, by pointing out many 

 methods of improving the microscope. 



On the 3d October 1826, Professor Amici wrote in the fol- 

 lowing manner to MM. Chevalier and Sons : " I have receiv- 

 ed your letter of the 24th September 1825, as well as the no- 

 tices and the memoir which you have addressed to me. In 

 thanking you for this present, which has been very agreeable 

 to me, I have learned, witli great pleasure, that you have ar- 

 rived at a perfect construction of achromatic object-glasses for 

 microscopes. This interesting part of optics has been general- 

 ly neglected, perhaps owing to the great diliiculties which it 

 presents, and science still requires that skilful opticians should 

 occupy themselves with the amelioration of the achromatism 

 in lenses of short foci. Naturalists will be happy to learn that 

 you have offered them microscopes according to the principles 

 of Euler, which surpass all dioptric microscopes. I hope it 

 will not be long before I shall have an opportunity of admir- 

 ing your instrument at Paris, and I shall then have the plea- 

 sure of showing you a small work of this kind, which, as an 

 amateur, I have constructed for myself." 



