740 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



These three examples differ from each other in detail, though they 

 are very similar in general construction, and are after the pattern as 

 made by Adams. 



The history of Microscopes focusing by means of a screw cut on the 

 barrel dates back to Campani in 16X6, though this arrangement was 

 preceded in 1665 by Hook, whose Microscope was focused by means of 

 a screw cut on the nose of the instrument. Grindl followed in 16-S7, and 

 Bonanni in 1691. Hartsoeker, in 1604, further developed this system 

 of focusing, and his instrument was clearly the prototype of the "Wilson, 

 which was published in 1702. Probably before 173* Culpeper applied 

 a pillar with folding tripod base to the Wilson model ; he also provided 

 an attachment by which it could be converted into a compound Micro- 

 scope. The Society possesses two examples of this instrument, the 

 workmanship of which is very beautiful. Finally, Adams produced his 

 model, which had a great sale, and was produced by other makers. 



Fig. 160. 



The instrument presented by Major Dennis is in very good condition. 

 It has five powers, the usual lens carrier for viewing opaque objects, and 

 forceps for holding the objects ; the stem of the forceps when thus used 

 is passed through small holes in the screwed barrel at the back of the 

 stage plates, as seen in the figure. These holes are referred to in 

 Adams' description, but are not visible in his figure of the instrument, 

 and this is the only example in the Society's cabinet — including the 

 Culpeper examples — that is provided with this particular method of 

 holding the forceps. There is also a double-ended box containing ten 

 slides, having forty objects mounted between talcs in the manner "then 

 common. 



Watson's Praxis and Bactil Microscopes.*— W. Watson and Sons 

 have recently brought out a new model, which embodies an advan- 

 tageous method of construction. Solid castings from specially constructed 



* W. Watson and Son's Special Catalogue (September 1905) 12 pp., 11 figs. 



