WINDOW LIGHTS AND THEIR VALUE. 357 



by no means contemptible. An illustration of this may be given. 

 While reading on the shady side of a railway car one afternoon, 

 a sudden flush of warm-tinted light seemed to cover the page and 

 as quickly it was replaced by a cold gray light. The change was 

 very noticeable and the cause easily revealed. At intervals along 

 the track were stretches of rough-faced masonry, perhaps seven 

 feet high. The stones looked in shadow a dull gray and a buff 

 color, but when the sun struck them they glowed with a light 

 that flashed into the car window. In spite of the fact that the 

 area of sky light was far the greater of the two, that rough retain- 

 ing wall determined in a great measure the character and inten- 

 sity of the illumination on the paper. 



Light- colored surfaces are the most valuable reflectors, and 

 among them white paint and whitewash stand pre-eminent.* Even 

 in shade, when illuminated only by other objects or by the sky, 

 they will give sixty per cent or more of an average sky light. 

 Sometimes they will run up to the full value of sky light, if a 

 reflecting surface near by shines brightly upon them, or they may 

 fall to twenty per cent or even less in deep shadow. But when 

 the direct rays of the sun fall upon a newly whitewashed surface, 

 the volume of light it reflects is almost blinding. Three hundred 

 to four hundred per cent is not too large an estimate to place upon 

 it in comparison with the sky light. On this account the well- 

 known expedient is used of whitewashing or painting in some 

 bright tint the walls of a light-shaft or surfaces facing a window 

 which is much shut in. A case is known of the rear of a house 

 so treated being in summer time a source of great annoyance to 

 dwellers on the next street, because of the blaze of light reflected 

 into their rear windows. White marble is quite similar in its 

 powers of reflection. A striking example can be seen in the spires 

 of St. Patrick's Cathedral in New York. Rising far above the 

 dust of the city, they are not yet covered with its grime, and 

 their pure white glistens in beautiful contrast to the dark blue 

 of the sky. 



From the white of paint or marble there are many variations 

 in building surfaces, all the way down to black. A large number 

 are to be found among the granites. Some varieties are very dark 

 in tone, reflecting little light unless polished, but the gray gran- 

 ites give considerable light. A freshly tooled gray granite will 

 certainly yield one hundred per cent of sky light when in sun- 

 shine, and some varieties give far more. The writer has known 

 the gray granite of an old building to give one hundred and forty 



* The percentages stated in the following pages are based upon a large number of pho- 

 tometric measurements of the light from building surfaces, made by the writer at various 

 times and places. 



