19 



NOTES. 



HoltzapffeTs Microscope. 

 By Edward M. Nelson. 



As Holtzapffel's Microscope, in which there are several original 

 details, is little known, a short account of it may be of interest. On 

 reference to fig. 16, it will be at once seen that the foot is similar to 

 that of Cornelius Varley's Micro- 

 scope,* inasmuch as it is a screw- 

 clamp for attachment to the edge of 

 a table, a form evidently suggested 

 by the stand of Wollaston's camera 

 lucida. The main stem, which is a 

 cylindrical rod with a groove in it, is 

 joined to the foot by a kind of uni- 

 versal ball-joint (not ball-and-socket). 

 A mirror slides on this rod, and it is 

 stated that the back of this mirror is 

 flat polished brass, so that monochro- 

 matic light may be reflected by it. 

 On the top of the rod is the lens- 

 (Wollaston doublet) holder (fig. 17); 

 this, instead of fitting in a V~S roove > 

 slides between three studs, of which 

 a and b are fixed and c loose ; e is 

 acted on by a spring so as to keep 

 the slide pressed against a and b. 

 This lens-holder is moved by the 

 milled head d ; but in place of a rack- 

 and-pinion gear, there is a steel tape 

 which takes a round turn round the 

 pinion, an end being fixed to each 

 end of the lens-holder; the screw e 

 is for the purpose of keeping this 

 tape taut. A similar mechanical de- 

 vice was, twenty years afterwards, 

 used by Ladd.f who fitted a steel chain with a turn round a pinion 

 for the coarse adjustment of his Microscope. 



The milled head / is for the purpose of rotating the lens-holder 



* Journ. R.M.S., 1900, p. 283, fig. 70. 



t Exhibited at the Great Exhibition, 1851. This movement is said to havebeen 

 applied to the Microscope many years previously by Mr. Julius Pftge. 



c 2 



Fig. 10. 



