38 



DESIGN. 



from various angles between the plane of the horizon, and within 

 two and a half degrees of the perpendicular. 



Bouguerh Table of Rays reflected from Glass. 



Of 1000 incidental rays, when the angle of incidence is 

 87^30', 584 are reflected. I 60^ 112 are reflected 



85^^, 543 '' 



82= 30', 474 " 



80=, 412 '' 



77= 30', 356 " 



75=, 299 " 



70=, 222 " 



65=, 175 " 



li 



u 

 II 

 ii 

 li 

 (I 



50=, 

 40=, 

 30=, 

 20^ 

 10=, 



1°, 



The slope of hot-house roofs, therefore, should depend on the 

 following circumstances : 



The latitude under which they are erected. — If in a southera 

 latitude, the plane of the roof should be as oblique as possible 

 to the sun's rays. South of 40=, the angle of incidence should 

 not be less than 20^. It will be recollected that this angle is 

 contained between the sun's rays and a perpendicular to the 

 roof. 



The position of the house, and the purposes for ivhich it is 

 intended. — Houses intended for the forcing of fruits in winter, 

 may have their roofs made on a perpendicular to the sun's rays 

 at that season. Conservatories attached to dwelling-houses may 

 also have their roofs perpendicular to the rays of the winter sun, 

 for the same purpose ; but blinds should be provided for them, 

 during the months of summer, to guard against the effects of 

 th* perpendicular rays when the sun is crossing his meridian 

 altitude. 



