IN ITS RELATION TO THE EYE. 459 



In the tables referred to on a previous page (footnote i, p. 445), 

 we have shown for the sake of completeness of representation the 

 gradation of surface brightness in three ways: (i) Brightness meas- 

 urements of prominent surfaces have been made. (2) Ratios have 

 been given between surfaces of the first, second, third, etc., order of 

 brilliancy, and surfaces of the lowest order of brilliancy; and be- 

 tween surfaces of the first, second and third order of brilliancy and 

 the brightness at the point of work. And (3) the mean variation 

 from the average and the percentage of mean variation have been 

 shown. In the consideration of these specifications a number of 

 single items might be selected as of possible significance in relation 

 to the efifect on the eye. Among these may be mentioned the order 

 of magnitude of the highest brilliancies; the average brilliancy; the 

 ratio of the highest to the lowest order of brilliancy ; the ratio of 

 the highest order of brilliancy to the brilliancy at the point of work 

 (brightness of test-object and reading page) ; etc. In order to see 

 which of these correlate most closely with the results of the test, 

 curves have been constructed in which some of these features are 

 plotted against the results of the test. These curves are given in 

 Charts III. and IV. In Chart III., B, percentage loss of visual effi- 

 ciency is plotted against the highest order of brilliancy, namely the 

 brightness of the reflector. In Chart IV. are grouped the remainder 

 of the curves. 



3. Translucent Direct Reflectors Differing in Density. 



In the fourth series of experiments it was decided to use the 

 same reflectors as were used in the third with one omission (the 

 blown Veluria) because of its close similarity to another in the series, 

 and to instal them in accord with the principles of direct lighting. 

 In this series was included also a set of reflectors of prismatic glass- 

 ware, differing somewhat from the others in size and design. They 

 will be designated by the numerals I., II., III., IV., V. and VI., num- 

 bered for convenience of treatment in the tables in the order of their 

 efifect on the eye from best to worst. Reflector I. is the pressed 

 Druid ; Reflector II. the blown glass toned brown (experimental) ; 

 Reflector III. the blown white glass (experimental) ; Reflector IV, 



