DEFECTS IN NEGATIVES. 129 



lately been discovered. A very little experience 

 will convince us, that others exist, which, owing to a 

 want of continuity between cause and effect, are in- 

 capable of demonstration, in the present state of our 

 knowledge. 



Some are certainly dimly present to our minds, 

 and although not fully recognised, are allowed for by 

 an unconscious cerebration, if we may be allowed 

 the term. 



The best method of arriving at a knowledge of 

 how to produce good negatives, is by studying the 

 defects of bad ones, endeavouring at the same time 

 to discover their cause, and the remedies for them. 



Inaccuracy in the preparation of solutions and want 

 of manipulative skill, are the principal difficulties 

 besetting a beginner. It will only be necessary to 

 mention where and how these inaccuracies are most 

 liable to occur, to enable the manipulator to guard 

 against them. 



When distilled water is mentioned never use any 

 other; pure spring water, not rain, being employed 

 for its production. Neutral solutions must be tested, 

 and what are sold as neutral salts can never be taken 

 upon trust, but must be made so. Obtain pure 

 chemicals ; see that all solutions are of the proper 

 strength ; keep all bottles requiring it tightly 

 corked ; and filter solutions when directed. Have 

 the dark room well ventilated, and on no account 

 allow a trace of ammonia to be present where the 

 wet plate process is employed. 



Among errors of manipulation may be classed 



E 



