PKOUEEDINGS OF THE SOCIETY. 415 



Yarley with a similar stage is described and figured in " Quekett on the 

 Microscope," 1848, p. 94. 



20. Jackson's Microscope. Date, about 1860 (?). (R.M.S. Cat. 

 No. 133.) Type — Compound : Achromatic. This stand was made by 

 Dr. George Jackson (one of the Founders and a President of the 

 Microscopical Society of London, now the Royal Microscopical Society). 

 The limb is in one piece and is planed straight through from end to 

 end in one cut, so as to form a dove-tailed groove in which the body 

 and substage move by means of rack-and-pinion. A fine-adjustment is 

 fitted to the stage ; the mirror is attached to the substage and moves 

 with it. The limb is mounted on two pillars which are screwed to a 

 horse-shoe foot, which is too small and gives an insufficient base. 



21. Thomas Ross. 1863. (R.M.S. Cat. No. x.) This is the 

 Microscope presented by Mr. Thomas Ross in exchange for the instru- 

 ment made for the Royal Microscopical Society in 1841 by Andrew Ross 

 (see Exhibit No. 16), and represents the ideal Microscope of the period. 



22. Ladd's Student's Microscope. About 1864. (R.M.S. Cat. 

 No. 145.) Type — Compound : Achromatic. This model is of an 

 original design,' differing in most of its features from all others of its 

 period. The body, stage, substage and mirror are fitted on a straight 

 grooved bar planed through from top to bottom, as in the Jackson 

 stand (see Exhibit No. 20). The substage has rack-and-pinion adjust- 

 ment, but the position of the mirror is fixed. The tripod foot is made 

 of light tubing, and has a fairly good spread of base. The coarse- 

 adjustment and the stage movements are operated by fine chains 

 workino- on spindles attached to the usual milled heads. The fine- 

 adjustment is worked by a loose lever hanging from the spindle of the 

 coarse-adjustment. 



23. Powell and Lealand. No. 1 Stand, 1869. (R.M.S. Cat. 

 No. 122.) Type — Compound : Achromatic. This model is a develop- 

 ment of their stand of 1848 (see Exhibit No. 18). It is dated 1875, 

 and with the addition of a fine-adjustment to the substage, rack-and- 

 pinion to the draw-tube, and diagonal rackwork to the coarse-adjust- 

 ment, the design remains unaltered to the present day. This stand was 

 preceded by one of a smaller size, which was probably introduced 

 after 1851. 



24. Ross's Binocular Microscope. 1878. (R.M.S. Cat. No. 40.) 

 Type — Compound : Achromatic. This is a Ross-Jackson model with a 

 Zentmayer swinging substage and a rotating stage with Turrell rect- 

 angular movements. The stage can also be placed at an angle with the 

 optic axis. The substage has rack-and-pinion and centring adjust- 

 ments. The tripod foot is cast in one piece with the uprights for 

 carrying the trunnions. 



25. Ross's Large Binocular Microscope. 1888. (R.M.S. Cat. 

 No. 186.) Type — Compound : Achromatic. The body is suspended by 

 trunnions on two pillars fixed on a modified horse-shoe foot. The 

 rotating stage has rectangular mechanical movements and a device for 

 tilting a slide towards the objective when using high powers in order 

 that the working distance may be ascertained. There is a rotating 

 Zentmayer substage with rack-and-pinion focussing and centring adjust- 

 ments. Schroeder's fine-adjustment is fitted to this instrument. 



