Observations on the Glazing of Hot-houses. 85 



sides, which may be called Horizontal Glazing. The incon- 

 veniences of this method, as usually performed, are that it 

 requires a considerable lap, to prevent the wet driving be- 

 tween the panes into the house, and thereby causing a drip 

 on the plants ; and when the lap is wide, the water, by the 

 attraction of the two contiguous surfaces, collects in it, and 

 in frosty weather becoming ice, expands, and occasions a 

 great breakage of the panes. This breakage is more exten- 

 sive when the sashes are laid with a slight inclination, so that 

 Green-houses which have sharp pitched roofs, escape 

 usually with less damage than Hot-houses and Pits, which 

 are generally less inclined. To obviate the injuries from 

 frost, the laps of the horizontal glazing are sometimes filled 

 with putty, which, indeed, is quite necessary in houses where 

 great heat is required, for when the laps are not filled the 

 warm air escapes rapidly through them, and a great waste of 

 heat is the consequence ; or, if a strong wind blows against 

 the front of the house, a contrary effect is produced by the 

 external air being forcibly driven into it between the laps. 

 The putty prevents these inconveniences, but as the con- 

 densed steam collected on the inner surface of the glass runs 

 down it at all points, it is stopped by the putty, and falls in 

 drops on the plants, a continuance of which is injurious. 

 These are the defects of the horizontal glazing, which is cer- 

 tainly the most economical, as well on account of the simpli- 

 city in the first execution, as of the facility with which it 

 can be repaired ; it is, however, less objectionable for the 

 reasons above given, when the roof lights are very much 

 inclined, or where a low temperature being required in the 

 house, the laps can be allowed to remain unfilled with putty, 



