64G 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



the Zeiss No. 1a stand, for preventing interference with the adjustments 

 by inexperienced persons at microscopical demonstrations. The stiff 

 cardboard capsules, which C. Zeiss supplies for covering the milled screw 

 heads of the rack-and-pinion coarse adjustment, the author proposes to 

 unite by a small bent metal bar, and instead of cardboard he would 

 make the caps of brass. The effect is to completely cover up the coarse 

 adjustment, and to place it beyond the risk of displacement. For 

 obtaining similar security with the fine adjustment, he, in the first place, 

 makes the) index pointer of rather stouter dimensions than usual, and 

 hinges it so that it can be folded up against the Microscope tube, while 



Fig. 14(5. 



the demonstrator is focusing. Two (or more if thought necessary) 

 little pins project 4 mm. about the rotating head of the fine adjustment, 

 so that, when the index is folded down, rotation of more than half a 

 circle is prevented. The observers would thus have a sufficient range 

 within which they could safely vary the focus. It would be best to 

 arrange so that for normal vision the pointer should be midway between 

 the two pins, and to obtain this it might be necessary to make some 

 change in the previous coarse adjustment. 



"Optical Arc Lamps.* — R. W. Paul makes these lamps in two sizes, 

 for 30 and 60 amperes (fig. 14G), the special features being the form of 

 horizontal traverse which gives a firm and even motion ; the construction 



* Catalogue Optical Convention, 1905, p. 198, fig. 6. 



