PROCEEDINGS OF Till: AMERICAN ACADEMY. 



to say that it is from the catalogue of a maker of reflectors who should 

 have known better. Note the blackness of the interior and the exces- 

 sive brilliancy of the li.u r ht on the work 



In this connection should be mentioned the trouble tluit may come 

 from the glare of light reflected from white paper, a risk to which book- 

 keepers are especially subject. I have been in counting dm mis where 

 I found every clerk with signs of bad eye- 

 Much paper is too highly calendered, and from this cause L r i 

 combination of regular and diffuse reflection. Obviously a mirror 

 placed on one's desk would give at certain angles an image of the lamp 



Figure 3. 



of distressing brilliancy, and as the head might move this image would 

 dodge into and out of the field of vision, giving an added cause of 

 trouble. Glossy paper does somewhat the same thing. Figure 4 shows 

 from Trotter's data 9 the relative reflection at various angles of inci- 

 dence from ordinary Bristol board (<t) and from the nearly pure matte 

 surface of freshly set plaster of Paris (h). The sharp peak corresponding 

 to the angle of regular reflection is very striking. Light on a desk 

 should therefore come from the side or rear rather than from the front, 

 especially if the source is of high intrinsic brilliancy. For a similar 

 reason the direction of illumination should be such as to free the eye 

 from the effect of wavering shadows of the hand or head. The avoid* 

 ance of shadow from the hand is the rationale of the sound old rule 



9 Tin.' Illuminating Engineer, 1. l v * 



