Microscopes of Powell, Boss, and Smith. By E. M. Nelson. 555 



Fig. 150. 



with the 8/10, 1/2, and 1/4 in. objectives. I have examined these 

 glasses, and have found them very well corrected. 



In 1846, Mr. Smith removed to 6 Coleman Street, E.C., and 

 entered into partnership with Mr. Richard Beck. Here the model 

 just described underwent two slight modifications, the more important 

 of which was the addition of the Jackson method of mounting the 

 limb on a trunnion between two pillars ; the second alteration was in 

 the stage, by placing the pinions of the rectangular motion in the 

 same plane as the stage, instead of at right angles to it. An alterna- 

 tive and cheaper form of stage was also made, viz. Alfred "White's 

 lever movement, described in a paper 

 read before this Society on November 

 15th, 1843. This movement was merely 

 Varley's with the handle of the lever in- 

 verted, i.e. pointing upwards instead of 

 downwards. Messrs. Smith and Beck's 

 No. 2 Microscope was the same as the 

 old one, with the exception that the 

 feet of the flat tripod were made to fold 

 for convenience of packing. 



A No. 3 or Student's Microscope, 

 which deserves special notice, was made 

 at this time. The limb was mounted on 

 a trunnion between two upright brass 

 plates supported by a flat tripod, very 

 similar to the Ross foot ; the position of 

 the fiat foot was however reversed, the 

 single toe being placed in front and the 

 two toes behind (fig. 149). The stage 

 was plain, with a sliding bar ; the body 

 was attached to the limb by the Jackson 

 rabbetted groove. The important point 

 about this instrument was its fine ad- 

 justment ; rising from the stage was a 

 strong triangular pillar, upon which the 

 limb could slide smoothly; this limb 

 was hauled down against an opposing 

 spring by means of a lever of the second order, placed below the stage, 

 as shown in fig 150. This was Smith's method of obtaining a steady 

 fine adjustment in conjunction with Jackson's rabbetted groove coarse 

 adjustment, and a very excellent plan it was, for it is still made, and 

 therefore has stood the test of fifty-five years' trial. 



In 1848, Messrs. Smith and Beck made the first concentric 

 mechanical stage ; this was the invention of Mr. M. S. Legg, and 

 was described by him in vol. ii. of our Transactions, p. 127, pi. 27. 



For the Exhibition of 1851 a new model was prepared, in 

 which an important alteration was carried out at the suggestion of 



2 p 2 



