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 not 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 



