Intensification of Photographic Pictures. 283 



remedy is found in chemical processes of intensification, but 

 modern gelatine plates do not always lend themselves well 

 to this treatment. 



The method now proposed may be described as one of 

 using the negative twice over. Many years ago a pleasing 

 style of portrait was current dependent upon a similar 

 principle. A thin positive transparency is developed upon 

 a collodion plate by acid pyrogallol. Viewed in the ordinary 

 way by holding up to the light, the picture is altogether too 

 faint ; but when the film side is placed in contact with paper 

 and the combination viewed by reflected light, the contrast 

 is sufficient. Through the transparent parts the paper is 

 seen with but little loss of brilliancy, while the opaque parts 

 act, as it were, twice over, once before the light reaches the 

 paper, and again after reflexion on its way to the eye. For 

 this purpose it is necessary that the deposit, constituting the 

 more opaque parts of the picture, be of such a nature as not 

 itself to reflect light back to the eye in appreciable degree — a 

 condition very far from being satisfied by ordinary gelatine 

 negatives. But by a modification of the process the objection 

 may be met without much difficulty. 



To obtain an intensified copy (positive) of a feeble negative, 

 a small source of illumination, e. g. a candle, is employed, and 

 it is placed just alongside of the copying- lens. The white 

 paper is replaced by a flat polished reflector, and the film side 

 of the negative is brought into close contact with it. On the 

 other side of the negative and pretty close to it is a field, or 

 condensing, lens of such power that the light from the candle is 

 made parallel by it. After reflexion the light again traverses 

 the lens and forms an image of the candle centred upon the 

 photographic copying-lens. The condenser must be large 

 enough to include the picture and must be free from dirt and 

 scratches ; otherwise it does not need to be of good optical 

 quality. If the positive is to preserve the original scale, the 

 focal length of the condenser must be about twice that of the 

 copying-lens. 



In carrying this method into execution there are two points 

 which require special attention. The first is the elimination 

 of false light reflected from the optical surfaces employed. As 

 regards the condensing-lens, the difficulty is easily met by 

 giving it a moderate slope. But the light reflected from the 

 glass face of the negative to be copied is less easily dealt with. 

 If allowed to remain, it gives a uniform illumination over the 

 whole field, which in many cases would go far to neutralize 

 the advantages otherwise obtainable by the method. The 



