170 Transactions of the Society. 



inclinable. The stage has rack-and- pinion focusing movement. 

 The body is fixed to a movable and rotating arm, and carries 

 Francois Watkins' rotating multiple lens-carrier nose-piece. The 

 mirror and condensing lens slide on the triangular pillar. 



Described and figured in Journ. E.AI.S., 1908, p. 365 ; and 

 1909, p. 657. 



The definition is not bad, the back lens introduced by Martin 

 making a slight improvement. Beyond this there is no special 

 feature or improvement. 



1 6. Jones s " Most Improved Microscope " (c. 1798). 



This model follows an earlier form of Francois Watkins, 

 inasmuch as the compass-joint making the Microscope inclinable 

 is raised to the top of an upright stem, fixed to a tripod folding 

 foot. To the joint is fixed a square limb, on the top of which a 

 short arm, movable by rack-and-pinion, supports the body of the 

 Microscope. The stage moves on the limb by rack-and-pinion, 

 which serves for the focusing of the object. The mirror and 

 condensing-lens slide on the same square limb. The object- 

 glasses are contained in a rotating multiple lens-carrier nose-piece. 



The instrument was described by its makers (W. and S. Jones, 

 of Holborn) as the " most improved " Microscope. This instru- 

 ment does, in fact, represent the culminating point reached by the 

 dioptric instrument before the introduction of the achromatic 

 objective. 



Described and figured in Adams' " Essavs on the Microscope," 

 2nd ed., 1798, p. 99. (See Journ. E.M.S., 1909, p. 657.) 



Tlie definition in this particular specimen is poor, and there is 

 a good deal of colour. A double mirror is attached to a separate 

 rod. The earliest known Microscope with a double mirror dates 

 from 1748. 



Class IV. — Eeflecting Microscopes. 



Although Eobert Smith had invented his reflecting Microscope 

 in 1738, with a condensing lens in front of the stage, the 

 Microscope when in use being in a horizontal position, it did not 

 come into general use, neither did that of Barker (1736), which was 

 also of the reflecting type. With these exceptions the optical 

 construction and definition did not vary till the introduction of 

 WooUaston Doublet and the Chevalier Doublet in 1820-30. Of 

 course differences of definition and field are found, owing to the 

 manner in which the lenses were ground and mounted, the most 

 careful workmanship naturally giving the best results. 



