IN ITS RELATION TO THE EYE. 455 



on account of their smaller size, came so low in the reflectors as to 

 change the distribution effects given by the reflector. For example, 

 without the socket extenders with these shorter lamps, the spot of 

 light on the ceiling, for the indirect system especially, was made 

 smaller and correspondingly more brilliant. It was considered to be 

 a point of interest in relation to the general problem to determine 

 whether this comparatively small change in illumination effects 

 would cause any difference in the eye's ability to hold its power to 

 sustain clear seeing. The results of the tests for the different in- 

 tensities of light for the three systems of lighting are shown in 

 Chart II. Space need not be taken here to represent the compara- 

 tive effects with and without socket extenders (see Trans. III. Eng. 

 Soc, 1915, X., pp. 473-476). In this connection it will be suffi- 

 cient for our purpose here to state that quite an appreciable dif- 

 ference in result was obtained especially in case of the 25-watt 

 lamps. These experiments constitute but one feature of a series 

 conducted to show the effects of faulty installation. 



2. Semi-indirect Reflectors Differing in Density. 



In the work under the first and second sets of conditions the 

 influence of differences in the distribution factors, more especially 

 surface brightness, was clearly revealed by the use of wide varia- 

 tions in illumination effects. In the third set of conditions much 

 smaller variations were employed. Such differences in effects were 

 included as could be obtained by employing semi-indirect reflectors 

 alone ranging from medium to dense. Six sets of reflectors were 

 used, similar in size and shape and differing only in density. These 

 reflectors were furnished by the Holophane Works of the General 

 Electric Co. (now Ivanhoe-Regent Works) with special reference 

 to the needs and purpose of the investigation. They are all of the 

 bowl type and 8 inches in diameter. Reflector I. is a pressed Sudan 

 toned brown; Reflector II. a blown white glass toned brown (an 

 experimental product); Reflector III. a pressed Sudan; Reflector 

 IV. a pressed Druid; Reflector V. a blown Veluria; and Reflector 

 VI. a blown white glass (also an experimental product). Reflectors 

 I., III., IV. and V. are commercial products, II. and VI. are in- 



