422 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



wiring, rheostat, and connexions for the house electric supply. The lamp 

 has all the necessary adjustments ; the condenser tube is telescoping, so 

 that the beam of light may be parallel or converging. At the end of the 

 condenser tube is a black disk for cutting off stray light, and serving as 

 a screen upon which the spot of light from the sub-stage condenser can 

 be thrown, thus serving as an aid in getting the mirror at the right angle 

 to send the light through the Microscope. The Microscope is supported 

 on an adjustable shelf which can be raised or lowered on the vertical 

 rods, thus enabling one to get any desired magnification. The vertical 

 supports for the Microscope shelf serve to carry a curved metal band to 



Fig. 59. 



support the cloth curtains to shade the drawing surface. There are two 

 curtains, and they hang freely, thus avoiding all interference with the 

 hands in drawing. If one desires, the arc lamp can be put in line with 

 the Microscope and the mirror turned aside. For a reflector beyond the 

 ocular a prism is used, thus avoiding any defects of a mirror. 



Beck Dark-ground Illuminator.*— Tiiis illuminator (fig. 60) con- 

 sists of a solid parabolic reflector, and has been designed to give so 

 much light that it can be used effectively with an incandescent gas- 

 burner. The light, which is focused upon the object, is all transmitted 



* R. and J. Beck, Special Catalogue, 1913. 



