THK PRODUCTION OF POSITIVES, ETC. 143 



under-exposure is all that is necessary for the pro- 

 duction of a good positive. We have found fifteen 

 seconds, three feet from an ordinary paraffin lamp, 

 sufficient exposure for a negative possessing the 

 characteristics recommended in a former chapter. 

 When no other means of printing but by contact 

 are available, a denser negative would give better re- 

 sults. 



Copying with the camera is to be preferred to 

 direct printing; first, because the exposure is length- 

 ened ; and secondly, because the character of the 

 resulting picture depends more on the size of the 

 stop, and intensity of the illumination than on the 

 density of the negative, and as a micro-negative is 

 less dense than an ordinary negative, greater power 

 of modifying the positive is placed in the hands of 

 the operator. Any form of doublet may be used. 

 The ordinary Petzval portrait combination is to be 

 preferred. It should be capable of taking a cabinet 

 picture. 



The ordinary quarter plate negative is the most 

 convenient to copy from, especially for enlarging, 

 because the pictures produced by a combination 

 covering that sized plate, are more perfect in detail, 

 and when artificial light is employed, it is possible to 

 obtaiu good illumination without the use of very 

 large condensers or equally large photographic com- 

 binations, which in addition to their costliness 

 possess inherent faults that cannot be corrected. 



If we desire a copy the same size or smaller than 

 the original ; the brass tube containing the lenses is 



