7 io THE POPULAR SCIENCE MONTHLY. 



ON THE CORRECTNESS OF PHOTOGRAPHS. 1 



By Dr. HERMANN VOGEL, 



PROFESSOR IN THE ROYAL INDUSTRIAL ACADEMY OF BERLIN. 



IN the previous chapters we have become acquainted with the de- 

 velopment and the theory and practice of photography, and have 

 mentioned cursorily various of its applications. It is our present pur- 

 pose to give special attention to one point which is of great import in 

 judging of the value of a photograph. 



Most persons have a fancy that the application of photography is 

 always uniform, whatever may be the object to be taken, and, there- 

 fore, that a photographer who can take a portrait must be able to 

 take equally well a machine, a landscape, or an oil-painting. This 

 results from the erroneous notion that the picture makes itself when 

 the photographer opens and shuts the lid. But our readers know 

 already that the picture does not make itself, but that it must be first 

 developed, brought out, fixed, and copied. In all these operations 

 there is no precise measure or rule how long the photographer should 

 expose to the light, develop, fortify, copy, and tone the picture. This 

 depends on his option and judgment ; and he is able at pleasure to 

 bring out the picture more or less in detail, according to the time of 

 exposure. Again, he can make it more or less brilliant, according to 

 the degree of strengthening ; he can make it more or less dark, ac- 

 cording to the mode of imprinting ; more or less blue, according as 

 he tones it down. But what is it that directs his judgment to deter- 

 mine if the picture is correct or not ? It is Nature, and Nature alone ! 

 He must know Nature, and compare it with his picture. Nor is this 

 easy. Nature appears positive to him, but in the picture she appears 

 first negative ; and, if he compares the two, he must be able in his 

 mind to convert the picture, that is, to change it and represent it as a 

 positive, which it is afterward to become. More comparing and study 

 is required to do this than is generally supposed. 



If two printed proofsare presented to a man who is ignorant of the 

 art of printing, one of the sheets in question being well and the other 

 ill printed, if the defects be not too glaring, this person will not be 

 able to detect any difference between the proofs. Far otherwise is it 

 with the practised eye of the printer, who immediately detects that in 

 one proof the type is too thick, or thin, or leaded, or that the letters 

 are faint, or blotched, or uneven. In like manner, a practised eye is 

 needed to judge a photograph an eye not only able to detect the 

 finest details of the picture, but also the peculiarities of the original. 

 The unprofessional man often uses the expression, " I have no eye for 



1 Abridged from the " Chemistry of Light and Photography," No. XIV. of the " In- 

 ternational Scientific Series." 



