106 ARRANGEMENT OP APPARATUS. 



or more in width, in preference to all other kinds ; it 

 is always obtainable, requires little care, and the ex- 

 pense incurred is very trifling. If properly employed 

 a negative can be taken by this light in five minutes, 

 with the one twenty- fifth, having a magnification 

 from 1000 to 5000 diameters, which will bear sub- 

 sequent enlargement to 50000 before the finest details 

 become visible to the naked eye. 



The Triplexicon lamp may be substituted for the 

 single wick form. It gives a brilliant illumination, 

 but on account of the great heat generated special 

 precautions must be taken to prevent injury to the 

 object and objective. It is also troublesome to 

 manage and difficult to prevent from smoking. 



Swan's incandescent lamp has numerous advan- 

 tages, among which may be mentioned the facility 

 of focussing, on account of the whiteness and bril- 

 liancy of the light, and the possibility of placing the 

 apparatus in any position during its employment. 



Care should be taken that the carbon filament 

 occupies the centre of curvature of the glass globe, 

 otherwise aberrations will be produced by the inclin- 

 ation of the surfaces j this might be avoided by par- 

 tially flattening the globe on two sides, one being 

 behind and another in front of the edge of the carbon 

 filament. 



The only serious objections to the use of Swan's 

 lamp for Photo -micrography, is the care and atten- 

 tion required when the electrical supply is produced 

 by a battery. The enormous expense entailed by 

 the purchase and working of dynamos, placing them 



