WARMING AND VENTILATING. 257 



hot-water tanks at Trentham a mixtm-e of pigeon-dung, in the proportion 

 of an ounce to a gallon of water, to supply this desideratum to vegetation : 

 others attain their object by watering the pots and beds with manured water, 

 in varying proportions, according to individual judgment. Mr. Beaton suggests 

 the application of vapour impregnated with tobacco or sulphur for the de- 

 struction of insects ; while Mr. Mcintosh recommends jniano, pigeon-dung, 

 and urine, used in the same manner by means of evaporating-pans attached to 

 the pipes, in order to attain the fumes of the old-fashioned dung-bed, "so pre- 

 eminently valuable for the restoration of sickly plants, and for promoting 

 the vigorous growth of healthy ones." 



697. We are indebted to the Dutch for the eai-liest edifices warmed with 

 artificial heat, as for initiation into many other gardening secrets. Their early 

 trade with the East developed a taste for flowers as early as the fifteenth cen- 

 tury ; and they soon found that their cold moist atmosphere was unfitted for the 

 successful culture of the delicate plants even of the Levant. They erected 

 houses for their reception, therefore, which they heated with the common 

 earthenware stove of the country, equahzing the heat by earthenware pipes 

 carried round the room. In course of time other countr}*»s adopted the idea, — 

 in our own country by means of open fires outside the building, with connect- 

 ing flues going round the house inside the walls ; and there are not wanting, 

 even now, gardeners who assert that as good crops of grapes were and are 

 grown by these flued walls, as can be produced by the modern innovations of 

 hot-water pipes. The invention and application was, however, a great disco- 

 very for horticulture ; and, accordingly, the names which are identified with 

 it are both numerous and eminent in their art. Our space will only permit 

 of our describing the principles on which the system acts, and name a few of 

 the leading inventions in general use. 



698. The principle upon which hot water circulating in pipes is applied to 

 warming houses is, that the hot water has a tendency to ascend, and to fall as 

 it cools ; the denser cold fluid displacing the more rarefied. This principle has 

 been extensively applied to warming public and other large buildings ; distance 

 from the furnace, and height above the boiler, being no obstacle to the circula- 

 tion 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 descends again by the return-pii^e, 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 principle is precisely that applied in heating horticultural build- 

 ings by hot water ; but as it is seldom necessary to raise the water for this 

 purpose, the amount of heat required is lower. Each hundred feet of 4-inch 

 pipe contains 544 lbs. of water, and will require 14 lbs. of coal to raise its tem- 

 perature to 180°. In a well- constructed boiler the water will lose 60° of heat 



