16 Transactions of the Society. 



III. — The First English Achromatic Objectives, 

 By Edward M. Nelson. 



{Head December ISM, 1901.) 



The Goring-Tullerj Triple (1824). 



This first English achromatic object-glass was made in 1824 by 

 W. Tulley,* the telescope-maker at Islington, at the suggestion of 

 C. E. Goring, M.D., who paid 90/. for it. An account of this historical 

 lens may be of interest. 



The back lens is an equi-convex of Dutch plate of specific gravity 

 2*519, thickness 0*175, the radii being 0*575. The middle lens is 

 an equi-concave made of Guinand's flint, specific gravity 3 * 627, thick- 

 ness at edge 0*164, and the radii 0*500. The front lens is a 

 biconvex crown of specific gravity 2*527, thickness 0*15, radius back 

 surface (next flint) 0*525, and front surface (next object) 0*825. 

 The focus of the combination is 0*933, diameter of the lenses 0*55, 

 the clear aperture * 50, the initial magnifying power 10 ■ 72, the N.A. 

 0*259, and the O.I. the large amount of 24*2. Fig. 15 A is drawn 

 to scale and is enlarged twice. 



The Chevalier-Euler Achromatic Doublet (1824). 



In 1823-4 Messrs. Vincent and Charles Chevalier, of Paris, made 

 an achromatic Microscope objective for M. Selligue. In this Micro- 

 scope the lenses of the objective were turned round the wrong way, 

 viz. with their convex surfaces facing the object. In the next year. 

 1824-5, Messrs. Chevalier brought out a " Microscope d'Euler," in 

 which the lenses of the object-glass were turned round the right way, 

 so that the plane side faced the object. 



The mention of Euler's name in the title of this Microscope refers 

 to the objective, the doublet of which it was composed being con- 

 structed upon principles published by Euler at St. Petersburg, in 1774. 

 The principle was the combination of an equi-convex crown with a 

 plano-concave flint, the radii of the three spherical surfaces being alike. 

 The data of the Chevalier-Euler cemented plano-convex doublet are as 

 follows. 



Back lens an equi-convex of plate glass, thickness * 072, radii * GC, 

 cemented to a plano-concave front lens of Guinand's flint, radius * 60, 

 thickness at edge * 074, diameter of the doublet * 36. Focus 1 * 65, 

 N.A. ■ 109, O.I. 18 * 0. These measurements, as well as of those above, 

 are in inches. Fig. 15 B is to scale and is enlarged twice. 



*. Also spelt Tully. 



