ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



93 



if ^V of a millimetre now measures 2 • 5 millimetres in the scale with the 

 coi-rect tube length of IGO millimetres, and a particular object glass, the 

 magnifying power of that object glass is 25. 



Sloan Objective Changer. — This apparatus, which is patented, takes 

 the place of the double or triple nose-piece, and has many advantages. 

 It consists of an adapter which has on one side a sloping projection A 

 with a bevelled nut 0. The adaptei' is clamped to the nose-piece of the 

 microscope by a screwed ring D, which is provided with stop, into which 



<& 



a halfpenny will fit, for tightening it up, and a series of loose fittings, 

 one of which is screwed on to each object glass. 



These can be readjusted by means of a spanner supplied for that 

 purpose, so that each lens can be centred with an accuracy that is never 

 possible with a revolving nose-piece. The object glasses can be inter- 

 changed almost as rapidly as turning a i-evolving nose-piece. 



(3) Illuminating- and other Apparatus. 



A New Microscope Illuminator. — The device, patented by Alexander 

 Silverman, which is here described has already come into extensive use 

 in the United States. 



The lamp consists of a ^-in. glass tube containing a single tungsten 

 filament. The tube is bent into a circle of 1-in. inside diameter and 

 l|-iu. outside diameter. It is made of colourless or blue (daylight) 

 glass, and silvered so that light is reflected downward from the circular 

 source to the object being examined. 



The lamp is operated at 0'9 ampere and 13 "5 volts for visual work, 

 and I'OG ampere and 18 volts for photographic work. Current from 

 an ordinary lighting circuit is utilized and controlled tlirough a special 

 rheostat (fig. 1) which contains a push-button switch for the lower 

 current and a spring contact for the higher one. 



An automatically adjustable support (fig. 2), provided with three 

 iris-like fingers, controlled by springs, is attached concentrically about 

 the objective. The lamp is held to the underside of the support by 

 two curved prongs and a perforated spring clip which slips over the 



