636 The Fundamental Laic j or the true 



greater and below unity when they are less than those of 

 the original. 



The writer has shown in the above mentioned Traill 

 Taylor lecture that even this wider rule requires modi- 

 fication if photographers are to be allowed to portray 

 psychological effects, e.g. moonlight, dazzling sunlight, etc., 

 as artists habitually do. 



Not only do the authors overlook Driffield's last paper 

 (loc. cit.) but they attribute views to later workers which 

 in the writer's belief it would be hard to find countenanced 

 by anyone. They say (p. 195, line A) : " This conclusion on 

 their part illustrates a prevalent fallacy that the range 

 of contrast on the exposure scales of the negative and of 

 the positive must be alike.'"' If such a fallacy does still 

 survive it is certainly not because the contrary has never 

 heen clearly pointed out, nor because practice gives it any 

 support ; and I believe the authors have unintentionally 

 misinterpreted the sentence from Jones, Nutting, and Mees' 

 paper which they quote in illustration. To me it seems 

 •clear that Jones, Nutting, and Mees are considering the 

 behaviour of a printing paper exposed behind a given 

 negative actually possessing a ratio of transparencies 

 greater than 1 : 5*6 and not a ratio of luminosities in the 

 original subject. 



Finally, seeing that soon after the publication of Lord 

 Payleigh's paper in November 1911 I published (Brit. 

 Journ.Phot. vol.lix. p. 289 ; Eder's Jahrlmch, 1912, p.* 106) 

 the first of a series of papers pointing out the feasibility of 

 doing what Porter and Slade show to be possible in their 

 Case II. p. 195, and that in the Traill Taylor lecture a general 

 method for solving all such problems by the method of 

 u reciprocal " curves was indicated, I confess myself com- 

 pletely at a loss to understand the authors' meaning when 

 they say concerning my last paper on the subject : " But he 

 certainly does not touch the validity of Hurter and Driffield's 

 •conclusions." 



It has been impossible for me to write a criticism of 

 th: j ir paper without reference to my own writings, but 

 I beg to assure the authors that I am less concerned about 

 establishing priority for my method of "reciprocal curves" 

 than anxious to remove the difficulties which their paper has 

 raised in the minds of many students of the subject. 



