WARD I AN CASES. 



555 WARMING, THEORY OF. 



box intended for the propagation of different 

 plants. It is constructed in such a manner 

 that it may be placed in a drawing-room, 

 or elsewhere in a dwelling-house. The 

 general appearance is that of a 2-light box 

 with glass sides, standing upon wooden 

 legs ; the bottom of the box being a zinc 

 tray or boiler containing water, which is 

 warmed by a lamp placed underneath it. 

 This tray or boiler is strewed evenly with 

 silver sand about an inch thick, kept 

 moderately damp ; and upon this sand 

 the pots with their different cuttings are 

 placed. " Those who possess the facili- 

 ties for propagating on the orthodox plan," 

 says Mr. Shirley Hibberd, " have no need 

 for Waltonian cases. To such they would 

 be mere toys ; but to people who want 

 only a few hundred plants for bedding, and 

 some scores of annuals for the borders, it 

 is the most useful invention of this more 

 than half-gone century, because it will do 

 whatever is done by dung-pits, hot-water 

 tanks, &c., on a large scale, and do it, 

 too, in precisely the same manner ; and 

 the only difference between a Waltonian 

 case and a propagating-house is as to 

 extent only." 



Wardian Cases. 



These cases are greenhouses in minia- 

 ture ; they may be made of any shape and 

 size, and to suit any situation, either out- 

 side or inside windows. At first they were 

 entirely enclosed in glass, as if hermeti- 

 cally sealed ; but experience has proved 

 that they are far more generally useful 

 when proper ventilation is provided. It is 

 obvious to remark that in smoky cities 

 such appliances are invaluable to those 

 who love flowers. 



Warming, Theory of. 



In no department of industrial art has 

 more ingenuity been exercised than in 

 applying heat, whether it be to houses or 



horticultural buildings. Stoves, furnaces, 

 and boilers, endless in form and principle 

 hot air, hot water, and steam have, in 

 turn, been adopte-d, approved, and super- 

 seded ; tubular furnaces, tubular boilers, 

 in an endless variety of forms, have been 

 invented, sometimes with most satisfactory, 

 at other times with doubtful results; but 

 while all have had, and have, their advo- 

 cates in the gardening world, no mode of 

 heating is so universally approved as hot 

 water circulating in iron pipes, with 

 bottom heat supplied from tanks heated 

 by the same means. 



The principle upon which hot water 

 circulating in pipes is applied to warming 

 houses is, that the hot water has a ten- 

 dency to ascend, and to fall as it cools ; 

 the denser cold fluid displacing the more 

 rarefied. This principle has been exten- 

 sively applied to warming public and other 

 large buildings ; distance from the furnace, 

 and height above the boiler, being no 

 obstacle to the circulation of the fluid, the 

 boiler being placed at the basement, while 

 a water-box is placed at the top of the 

 building, both being hermetically sealed. 

 A flow pipe connects and carries the hot 

 water from the boiler to the water-box. 

 After passing through it, the water de- 

 scends again by the return pipe, and by its 

 greater density displaces a like amount of 

 hotter fluid on the surface. A supply 

 pipe, regulated by the ordinary ball-cock, 

 admits cold water into the water-box to 

 replace that withdrawn by evaporation, 

 while safety valves, placed on the boiler, 

 guard against too great a pressure from the 

 expansion of the water. This is the prin- 

 ciple that is applied in heating horticultural 

 buildings by hot water ; but as it is seldom 

 necessary to raise the water for this pur- 

 pose, the amount of heat required is lower. 

 Each hundred feet of 4-inch pipe contains 

 544 Ib. of water, and will require 14 Ib. ot 

 coal to raise its temperature to 1 80. In a 



