166 



GAEDEXIXG FOE PLEASURE. 



quarter spans ; " that is, haying nearly two-thirds of the 

 roof long on one side and the other one-third on the other. 



The long or two-thirds 

 side should in all cases, 

 as near as possible, slope 

 directly south, the ob- 

 ject being to obtain, dur- 

 insr the dull davs of win- 

 ter, as much sunlight as 

 possible ; and for the 

 same reason the wood 

 work of the frame should 

 be as light as possible, 

 and the glass of the 

 largest size that can be 

 economically used. The 

 average size now in use 

 for this purpose is twelve 

 by twenty inches, put in 

 the twelve inch way. 

 The brand of glass most- 

 ly used is what is known 

 as ^^second quality dou- 

 ble thick French." It 

 is of the utmost impor- 

 tance that the glass be 

 clear and without flaws; 

 otherwise the flaws will 

 concentrate the sun's 

 rays, forming lenses, 

 and burn the foliage. 

 When greenhouse struc- 

 tures are not wanted 

 specially for winter flow- 

 ers or fruit, they may be formed of equal spans, as in 

 figure 55. In this case the ends should face north and 









