ILLUMINATING APPAKATUS 



47 



for colour screens or ground glass. It is supported on a rod (L) 

 which moves backwards and forwards parallel with the optic 

 axis for obtaining either parallel or convergent light, and can be 

 clamped in any position. 



If the condenser is not required it can be swung to one side ; 

 or if it is required to use colour screens alone, the lens of the con- 

 denser can be removed from its mount. 



The illustrations show the lamp (Fig. 38) for use with the mirror 

 of the microscope for transparent or dark- ground illumination 

 by means of a dark-ground condenser, or for metallurgical or 

 photomicrographic work. Fig. 39 shows it tilted for use without 

 a mirror, or Fig. 40 

 shows it arranged for 

 the illumination of 

 opaque objects from 

 above. 



The lamp is pro- 

 vided with a ground 

 glass and a signal- 

 green glass ; it is com- 

 pleted by the addi- 

 tion of the Wratten 

 & Wainwright's colour 

 filters and the neutral 

 glass moderator. It is 

 provided with 12 feet 

 of cable and an at- 

 tachment for fitting it 

 to a lamp fitting of 

 an ordinary house 

 supply. For use 

 with the " Pointolite " 

 lamp, which is an in- 

 candescent disc about 

 the size of a small 



peppercorn, a direct Current of any voltage from 100 to 250 

 volts is equally satisfactory, a variable resistance being supplied 

 to adapt it to any current between these limits. The candle- 

 power is 100, but as it is all concentrated in the one point it is 

 at least twenty times as powerful as the filament lamp focussed 

 with the condenser. 



If a 100-candle-power 1/2- watt lamp or 40- or 60-candle- 

 power metal filament lamp is used, it is suitable for either 

 direct or alternating currents, and for a voltage from 100 to 

 200 volts, although a lamp suitable for the voltage must be 

 selected. 



No special wiring is required, any ordinary house current 



being sufficient. 



Fig. 40.— No. 3332, "Pointolite" Lamp. 



