ILLUMINATING APPARATUS 



45 



object readily should be used, and no more. If this precaution 

 is taken, microscopists need have no fear of injuring their eyes, 

 however long they work. The light should be more powerful 

 than is required for general purposes, it should be powerful 

 enough for dark-ground illumination and to allow of the use of . 

 colour filters. 



Fig. 36 shows a good form of parafhn lamp for microscopic Paraffin 

 work. It has a single flat wick 5/8 inch wide. The burner ^^™p* 

 has a revolving motion and may be used with its edge facing the 

 mirror to give a strong illumination, and with the flat surface 

 facing the mirror for a softer light. It has a means of raising 

 and lowering it from the table to enable it to be used for illumina- 

 ting opaque objects with a bull's-eye condenser or parabolic 

 reflector, or for setting it to the correct height for using the 

 vertical illuminator described on page 41. 



The reservoir and burner are carried on a support which 

 passes through the centre of the reservoir so that the weight is 

 well balanced over the centre of the stand. The lamp glass is 

 simply a 3 X 1-inch microscope slip carried in a thin metal 

 chimney. The burner is insulated from the reservoir by a fibre 

 ring, which is always cool enough to touch for turning the burner 

 round. The metal chimney can be removed and the burner 

 hinged back for trimming the wick. The reservoir has a large 

 screw stopper for filling. A bull's-eye condenser on a separate 

 stand may be used in combination with this lamp for illuminating 

 opaque objects or 

 for high - power 

 dark- ground illu- 

 mination, al- 

 though this lamp 

 is not recom- 

 mended for the 

 latter purpose. 



The ordinary 

 electric incan- 

 descent lamp pro- 

 vided with a 

 frosted or ground 

 glass bulb is a 

 handy lamp for 

 ordinary observa- 

 tion, but is not 

 sufficiently bril- 

 liant for many purposes. It is supplied on an adjustable table 



stand. 



The best equipment is the " Pointolite," or 1/2-watt " Grid" 

 lamp, with a neutral glass double wedge, a set of colour screens, 

 and a bull's-eye. It does everything that is required for every 



Electric 

 lamp. 



Fig. 37. — No. 3336, Electric Lamp on Stand. 



