30 Transactions of the Society. 



" We had a very nice lecture from Dr. Grant this morning. I 

 mean to ask him thy question when we get to polypifera again. 

 " With dear love to all at home^ including Eickman and Mary, 



I remain, thy affectionate Son, 



Joseph Lister." 



[There is abundant evidence in the loose papers that J. J. Lister 

 kept in close touch with the leading Opticians — Andrew Ross, Powell, 

 and Smith more particularly — and that he took particular interest in 

 the work of the last-mentioned, as will be seen from the following 

 entertaining— if rather pedantic — instructions, which, in certain quarters, 

 and mutatis mutandis, might be worth hanging up as a useful reminder 

 at the present day :] 



" Queries for J. Smith to go over on finishing a Microscope. 



Do they screw home ? 



Are they Avell centered, and is false light 



stopped ? 

 Do their tubes slide freely, but safely ? 

 Are they notched to fit the pin ? 

 Do the Lieberkuhns illuminate well ? 



Is the rack-work action in order ? 

 Is the slow-motion in order ? 

 Does the tube slide easily ? 

 Is reflected light stopped ? 



Are the glasses of right focal length and 



size ? 

 Are they at right distances ? 

 Are the stops in the right place and fixed ? 

 Are the caps of right length and fitting on 



^vell ? 



Are its three actions easy but steady ? 

 Does the mark, when set to the line on the 



Imr, make it central, and are both 



distinct and black ? 



Are the rack work actions in order through- 

 out ? 



17. Does the slidingr-tube slide and revolve 



smoothly and firmly, and without moving 

 the rack work ? 



18. Does the clamping-piece slide as easily as 



the sliding plane ? 



19. Diaphragm . Are its holes numbered ? 



20. Does it fit on easily, and is its action in 



order ? 



