Memoirs of the Caledonian Horticultural Society. 335 



ing the pipes, with openings left between each piece. The pillars must be 

 so placed that they shall not intercept the steam issuing from the blow- 

 holes. This cover prevents any pressure of the stones upon the pipes. 

 Were this not attended to, the repeated motion of the pipes among the 

 stones, in expanding or contracting, would soon shake or rend the whole 

 building. The first three layers of stones at the bottom of the steam- 

 chamber are 4§ to 4 in. in diameter ; they are then gradually reduced from 

 4 to 3i, 3 to 2,\ and 2 in.; the layers near the top are about the size of 

 hen's eggs, those above about the size of pigeon's eggs, and the levelling 

 rows at the top that of large marbles. 



" The covers (r) of the steam-chamber are of Arbroath pavement, 2£ in. 

 thick, half-checked on each other, and laid down so as to rest upon the 

 top of the pillars c c, pressing gently on the small stones below, and closely 

 jointed with Roman cement. Where proper flags cannot be procured, 

 some of these pits have been covered with checked bricks made of fire clay, 

 18 by 9 in., and laid on cast-iron rafters. 



" The covers of the steam-flues (r r) are laid in the same manner ; they 

 are 2\ in. thick, and let into the sides of the flues with a half-inch check. 



" s s, Cast-iron steam-tubes, with lifting covers ; the tubes are 2\ in. 

 diameter, by the same in height. On the bottom of the tubes, a square 

 piece is cast, which is sunk into the top of the cover of the steam-flue, and 

 fixed with lead. By lifting the covers of the tubes, the steam, which is 

 greatly modified before it reaches them, will emit a moist heat to the plants, 

 and even raise the temperature; and, by replacing the covers, the heat will 

 be immediately withdrawn. 



" s, Represents about 4 in. of furnace ashes. 



" 1 1, A. movable piece of wood, to raise the bed of earth for the plants 

 near the glass, if required. 



" t, Boiler, with gauge cocks and safety valves, &c. 



" u u, The alarm pipe dipping in the boiler a little below the lowest 

 gauge cock. Shouldany accident prevent the regular supply of the boiler 

 with water, as soon as it has evaporated to this level, the steam rushes up 

 the pipe, producing a loud whistling noise, and giving notice to the gar- 

 dener that his attendance is required to the boiler. 



" u, Feeding cistern, with hydrostatic balance and valves. I may mention 

 here, that steam, at a moderate pressure, of from 1 lb. to 2 lbs. per square 

 inch, is, in my opinion, better adapted for the purposes intended by these 

 pits than steam at a higher pressure. 



" v, Cistern and ball-cock for supplying the boiler, having a waste-pipe, 

 about three fourths of an inch higher than the water stands in the boiler, 

 with a cock which drains both the cistern and the boiler, when it is neces- 

 sary to clean them. It was first designed to supply the boiler of the steam- 

 pits at Cunnoquhie by a feeding apparatus ; but it was afterwards thought 

 that the gardener would manage it with more ease, if it were supplied with 

 water from a small cistern connected with it on the same level, and the 

 cistern fed by a properly constructed cock, and half globular ball ; the 

 steam being thus blown upon the stones in the steam-chamber at the 

 atmospheric pressure. 



" / 1, on the ground plan, Slide valves or cocks. The case of the valve 

 is of cast-iron, with a brass slide fitted into the inside, and a stuffing-box, 

 and cross-headed handles. These valves admit the steam into either of the 

 pipes at pleasure, or into both at the same time; and when this is the 

 case, that there may be a sufficient supply of steam for both, the bore of 

 the pipe (x) is made 4 in. 



" The furnace being finished, and the pipes laid, the passages for the 

 pipes into the pits w w are firmly stuffed with dried moss, and two pieces 

 of stone are prepared to fit the circumference of the pipes, leaving no more 



