34 



WINDOWS AND SKYLIGHTS 



FIG. 150. 



however, under ordinary conditions shades are necessary when bright 

 sunlight strikes the window. The glass used in factory ribbed and 

 rough plate glass as made in England is somewhat opaque, and the 

 atmosphere is somewhat hazy, so that the use of shades in their shops 

 is in most cases unnecessary. The glass made in this country is so 

 clear and our atmosphere is so translucent that it has been found nec- 

 essary to use shades where windows and shades are exposed to direct 

 sunlight. The most effective and satisfactory shade is a thin white cloth, 

 which cuts off about 60 per cent of the light. 



Size and Cost of Glass. The regular stock sizes of plane glass 

 varies from 6 x 16 inches by single inches up to 24 x 30 inches, and above 

 that by even inches up to 60 x 70 inches for double strength glass and 

 30 x 50 inches for single strength glass. 



The weights of different thickness of glass, assuming 156 pounds 

 as the weight of one cubic foot of glass are given in the following table : 

 WEIGHT OF GLASS PER SQUARE FOOT. 



Thickness-in y 8 3-16 % % V 2 % % 1 



Weight Ibs 1.62 2.43 3.25 4.88 6.50 8.13 9.75 13 



The cost varies with the quality and the size, being about twice as 

 much to glaze a given area with 30 x 36-inch lights as with 10 x 12- 

 inch lights. The discounts given from the standard price list vary so 



