658 summary of current researches relating to 



Class 5. — Instruments Fitted with Achromatic Objectives. 



DELLEBARRE'S "Microscope Universel." About 1777. 

 Type — Compound : Achromatic. 



This stand is a French model on the lines of the English Microscopes 

 of the period. The square limb is fixed on to a scrolled folding tripod 

 foot, and has a hinge about its middle by means of which the upper part 

 can be inclined. The body is fixed to an arm which slides in a rotating 

 socket at the top of the limb. The concave mirror and condensing lens 

 slide on the limb. The arm carrying the stage has a pinion moving in a 

 rack cut in the limb for the purpose of focusing. 



Dellebarre endeavoured to obtain achromatism by the use of oculars 

 built up of crown and flint glass lenses, the excessive correction of the 

 ocular compensating for want of correction of the objective. His plan 

 was not, however, successful, and the first practical achromatic Micro- 

 scope was not produced until fifty years after his time. 



Described and figured in Petri's "Das Mikroskop," p. 162. 



LISTER-TULLEY Microscope. Made by James Smith, 1826. 



Type- — Compound : Achromatic. 



This Microscope was designed by Mr. Joseph T. Lister, who also 

 himself made an achromatic object-glass for it. This is the first achro- 

 matic Microscope made in this country. A folding tripod foot supports 

 a pillar, on the top of which is hinged an arm which supports a body 

 having two draw-tubes and a focusing rack at the side. A substage is 

 provided, fitted with a compound condenser. The stage has rectangular 

 movements by means of two pinions, one of which is placed in a vertical 

 position. Steadying rods are used to support the body in the inclined 

 and horizontal positions. 



Described and figured in Journ. R.M.S., 1900, p. 550. 



Lent by Mr. E. M. Nelson. 



CHEVALIER " Microscope Achromatique." 1834. 



Type — Alternatively Simple or Compound : Achromatic. 



The brothers Chevalier, of Paris, were the first opticians to produce, 

 about 1823, practically useful achromatic object-glasses for the Micro- 

 scope. The present instrument is an early specimen made by Charles 

 Chevalier. The mechanical model followed is still that of Jones's " most 

 improved," with various modifications. The arm carrying both the body 

 and the limb is fixed by a compass- joint to the top of the stem, which 

 itself is supported on a flat solid tripod. Focusing is effected by rack- 

 and-pinion to the stage, w T hich itself is mechanical in one direction only. 



Described and figured in Chevalier's " Des Microscopes et de leur 

 Usage," 1839, pp. 98-100, pi. 3. 



