

4:2 



GREENHOUSES 



to 500 feet or more. A discussion of the ad- 

 vantages of high, wide, single houses and of 

 low, narrow, connected houses is given in 

 Chapter IV. 



Pitch of Roof. The pitch of a roof means 

 the degree of slant or the angle of divergence 

 from the horizontal. The glass of the roof 

 not only allows the light, heat and chemical 



Fig. 24. The pitch of the roof is measured at A 



rays to pass through it, but it also acts to 

 some extent as a mirror, thus reflecting a 

 part of the rays. The amount lost by re- 

 flection is proportional to the angle of in- 

 cidence. Thus, if the sun's rays fall upon 

 the roof at right angles, little or none is lost 

 by reflection; but when they fall at a less 



