DESIGN. 



35 



In England, the most common elevation of roof is an angle of 

 45°, which, in the latitude of London, would form a perpendic- 

 ular to the impinging ray, about the beginning of April, and the 

 beginning of September, — which also makes the obliquity of 

 the rays greatest when they are most powerful, viz., during the 

 month of June. " This angle is preferred by most gardeners," 

 observes Loudon, " probably from habit." We think, however, 

 that something more than mere habit justifies the adoption of 

 this angle, — more especially for forcing-houses, — since by it 

 the benefit of perpendicularity is obtained at a period when the 

 rays are comparatively feeble and most necessary. 



Fig. 1. 



As some of our readers may hot have made themselves suffi- 

 ciently acquainted with the altitude of the sun in relation to the 

 slope of hot-house roofs, we have annexed the above figure, 

 (Fig. 1,) which represents the slope of five different roofs on the 

 angles marked by their respective complements. / represents 

 4 



