292 Transactions of the Society. 



instrument, as it is very similar to the No. 1 stand as at present 

 made (see fig. 84). The differences between them are as follows : — 

 the tripod foot is smaller, but similar in every other respect ; the 

 stage has non-concentric rotation ; in the substage the pinion for 

 rotary motion is placed in a vertical instead of a horizontal position 

 as at present, and the substage apparatus screws into the substage. 

 The back-stay fitted to the bodies of the previous models is omitted- 

 This was the first Microscope made by this firm that had a complete 

 substage; in this 'point it was probably a copy of the Microscope 

 Andrew Ross prepared for the Exhibition of 1851, at which Messrs. 

 Powell and Lealand were not exhibitors. 



The next Microscope was brought out in 1861, and was figured 

 anil described by Mr. Lobb in the Quarterly Journal of Microscopical 

 Science* The instrument (fig. 83) is about the same size and is 

 very similar to the present model, the principal difference being in 

 the arrangement of the concentric rotation of the stage. A large and 

 massive ring is firmly attached to the limb of the Microscope ; inside 

 this ring there is a second ring capable of being rotated by rack-and- 

 pinion ; to this second ring is attached a short and stout limb 

 carrying both the stage and substage. When therefore the stage 

 is rotated, the substage rotates with it. This stage, like that of all 

 Powell's Microscopes, had Turrell's rectangular mechanical move- 

 ments, and the substage had rectangular and an independent rotary 

 movement as well. The pinions for rotating both the stages, as well as 

 for the independent rotation of the substage, are placed in a vertical 

 position ; but in an example I have seen, dated 1866, they are placed 

 horizontally. The Turrell stage of this Microscope was made much 

 thinner than those of the previous models ; this permitted a very oblique 

 beam of illumination to be thrown upon the object from below the 

 stage — a point which in those days was thought to be of much import- 

 ance. This Microscope is fitted with a Wenham binocular, in such 

 a manner that the binocular tubes can be removed and a monocular 

 tube substituted for them ; this method of mounting the binocular body 

 is still retained in the No. 1 Microscope as at present made. Wenham 

 described this excellent form of binocular in the Transactions of the 

 Microscopical Society f ; and as this Microscope was finished about 

 May 1861, it follows that it must have been one of the first Micro- 

 scopes to be fitted with a Wenham binocular. Powell was the first 

 to adapt rackwork to the tubes to adjust the instrument for different 

 widths between the eyes. In my opinion, the Wenham binocular 

 is the best and most generally useful binocular that has as yet been 

 invented. 



The next and last Microscope is the present No. 1, which was 

 brought out in 1869, and which, strange to say, has never been figured 

 or described in our Journal. It will be seen from fig. 84 that it does 



* Vol. i. n.s. (1861) p. 175. 



t Vol. ix. p. 15 (1861), paper read December 12th, 1860. 



