PRACTICAL PHOTOMICROGRAPHY. 



139 



In the first place, an artificial light is used, and that light 

 not remarkably powerful or actinic in comparison with day- 

 light, and, moreover, the light is used in a lantern and 

 not many inches distant from the original which is to be 

 enlarged. So in the absence of a condenser we should have not 

 only a weak but an uneven light, for the margins of our 

 original would be much less strongly lighted than the centre. 

 We here give a cut which will explain the functions of a con- 

 denser. 



FIG. 3-4. 



A is the radiant ; B^ a condenser of two elements ; (7, the 

 original negative or positive held in frame E ; the front focus 

 of the condenser falls at a point inside a doublet lens 1), the 

 rays having passed through the original, except some marginal 

 rays which might be used but are stopped by portions of the 

 frame E. 



Theoretically the radiant should be a point, and that point 

 accurately in the focus of the condenser. Practically we can- 

 not get such a point, the electric arc approaches most nearly 

 to a point, the oxy-hydrogen mixing- jet lime-light next, a 

 " blow-through " lime-jet perhaps next, and so on down to the 

 worst of all a multiple- wicked oil lamp. Still even the three- 

 wicked lamp may in practice be successfully used, especially if 

 we adopt an ingenious little contrivance due to Mr. Traill Taylor 

 (Editor of the British Journal of Photography). Mr. Taylor's, 

 suggestion was a simple converging lens placed between the 

 light and the condenser, the supplementary lens collecting rays 

 that would otherwise not reach the condenser. 



The area of the condenser must evidently be not less than, 

 and ought to be greater than, the area of the portion of the 

 original we propose to enlarge. The diameter of the condenser 



