1900] MICROSCOPICAL JOUHJVAL. 7^ 



Dark Ground Illumination. — The size of tlie stop 

 must be proportioned to the aperture of the objective ; 

 the higher the aperture the larger the stop. Try making 

 various stops for yourself out of blackened cardboard. 



Dissecting. — It can be done with the simplest appiara- 

 tus, but some form of dissecting microscope or stand is a 

 great convenience, and an actual necessity where much or 

 prolonged work is done. The microscope itself can be 

 used together with the lowest-power objective,but in this 

 case; the image will of course be inverted, unless what is 

 called an "erecting lens" be used. To protect the stage, 

 Mr. West's table stage, is a most simple and practical 

 device ; it is provided with hand-rests, and can be used 

 also as a mounting-table. There are, of course, different 

 types of dissecting-^tands made by the opticians, of which, 

 perhaps, the cheapest is Leitz's small dissecting micro- 

 scope, sold at $5 without lenses. A small stand can be 

 made at home by any one able to use his hands, and that 

 will cost but a few shillings. The design itself is not or- 

 iginal, as a similar but more elaborated stand is figured 

 in opticians' catalogues at $10. and upwards. Tho total 

 length should be about 14 inches, and the width about 4 

 inches. The sloping rest for the hands might be, say, 2 

 inches high at the lowest ends, and 4 inches at the high- 

 est. This latter measurement, however,should be govern- 

 ed by the size of the mirror, which must have ample room 

 to swing. The mirror itself is a simple penny mirror such 

 as can be bought at any toy-shop, and it is let into a piece 

 of wood which swings on wooden or metal pivots between 

 the two centre uprights. This piece of wood could be 

 hinged to the bottom of the stand instead ; but in that 

 case the mirror would not remain central when lifted at 

 an angle. A little more skill would be required to ar- 

 range universal movements. The stage is a piece of plate- 

 glass 5 inches x 4 inches, ground at the edges, and can 

 be ordered at any glazier's. It lifts out, if necessary. 



