JAN.] THE HOT-HOUSE. 89 



working down along the edges of the sash frames : these rafters 

 must be narrowed on the under side, the better to admit the rays of 

 light and heat. 



The lights are to be laid on, in two ranges or tiers, sliding one 

 over the other, of sufficient length together, to reach quite from 

 the top of the upright framing in front, to the top of the back wall: 

 if these lights be placed close together, the rafters must be grooved 

 lengthwise, above, to carry off* the wet which may fall between 

 them ; making the upper end of the top tier, shut close up to the 

 wall-plate, running under a proper coping of wood or lead, fixed 

 along above close to the wall, and lapped down with due width to 

 cover and shoot off the wet sufficiently from the upper termination, 

 of these sashes : likewise along the outer edge of the top or crown- 

 plate in front, may be a small conductor of lead or wood, to receive 

 the water from the slope-glasses and convey it to one or both ends, 

 without running down upon the upright sashes ; being careful that 

 the top part behind is well framed and secured, water-tight, and 

 finish the top of the back wall a little higher than the glasses, with 

 a neat coping the whole length. 



In every part, the wood-work must be made with the most criti- 

 cal exactness, and all the sashes so fitted as to slide close and free ; 

 neat stays of iron may be placed on the under side of the roof lights, 

 sunk into the wood and made fast by wood screws, in order to 

 strengthen them ; and the rafters or cross-bars are to be stayed 

 with wood, at proper distances, to keep each firm in its place. In 

 wide stoves it will also be necessary to place a neat upright, either 

 of wood or iron, inside, under each of these rafters, to prevent their 

 bending under the weight of the glasses, which are generally made 

 to rest on the back-wall of the bark-pit. 



In glazing the roof-lights the panes are to lap over each other 

 about half an inch ; the vacancies where they overlap are by some 

 closed up with putty, others leave them open, which is the better way 

 when not too wide ; in order both for the air to enter moderately, and 

 for the rancid vapours, arising from the fermentation of the bark- 

 bed, &c. within, thereby to be suffered to pass off; and also that such 

 as condense against the glasses, may discharge itself at those places 

 without dropping upon the plants : the glass for this purpose should 

 be of a small size, and not more than from six to eight inches 

 square ; such would lap closer than larger sized glass, and form a 

 much stronger roof. The great apertures occasioned by the crook- 

 edness of large panes admit the cold air so copiously in severe 

 weather, that incessant fires must be kept up to counteract it, which 

 certainly is injurious to the plants ; but of two evils you must take 

 the least; and, besides, an extraordinary quantity of fuel is consum- 

 ed this way which might be saved, and the plants kept in better 

 health, by adopting the smaller sized glass. Generally when a 

 large pane is pinned down, so as to form some kind of a close lap, 

 it presses so hard on the other, that one of them, and sometime? 

 both crack:, which permits the rain to run down frequently on 

 plants that too much moisture in the winter season will absolutely 



