192 



HEATING AS APPLIED IN HORTICULTURE. 



vessel, containing water of the same tem- 

 perature, coated with writing paper, will 

 radiate 98 parts of heat ; rosin, 96 ; 

 China ink, 88 ; red lead or isinglass, 80 ; 

 plumbago, 75 ; tarnished lead, 45 ; tin 

 scratched with sand paper, 22 ; mercury, 

 20 ; clean lead, 19 ; polished iron, 15 ; 

 tin-plate, 12. In order to ascertain the 

 velocity of cooling for a surface of cast- 

 iron, Hood selected a pipe 30 inches long, 

 2 J inches diameter internally, and 3 

 inches diameter externally. The rates of 

 cooling were tried with different states of 

 the surface : first, when covered with the 

 usual brown surface of protoxide of iron ; 

 next it was varnished black ; and finally 

 the varnish was scraped off, and the pipe 

 painted white with two coats of lead paint. 

 The ratios of cooling 1° were found to be, 

 for the black varnished surface 1.21 

 minutes; for the iron surface, 1.25 mi- 

 nutes ; and for the white painted surface, 

 1.28 minutes. These ratios are in the 

 proportion of 100, 103.3, and 105.7 ; but 

 as the relative heating effect is the in- 

 verse of the time of cooling, we shall find 

 that 100 feet of varnished pipe, 103f feet 

 of plain iron pipe, or 105f feet of iron 

 pipe painted white, will each produce an 

 equal effect. Leslie found that tarnished 

 surfaces, or such as are roughened by 

 emery, by the file, or by drawing strokes 

 or lines with a graving tool, had their 

 radiating power considerably increased. 

 But according to Melloni, the roughness 

 of the surface merely acts by altering the 

 superficial density, which varies according 

 as the body is of a greater or less den- 

 sity, previous to the alteration of its 

 surface by roughening." — Tomlinson on 

 Warming S$c. 



With the view of abstracting the su- 

 perfluous heat which is found to sur- 

 round all furnaces and boilers, and 

 which, in general, is allowed to diffuse 

 itself through the building which encloses 

 the boiler, or go to waste in the stoke- 

 hole, and to carry it into the interior of 

 the house to be heated, the following 

 system is practised by Mr Henderson of 

 Oxton Hill nursery, Birkenhead, in some 

 houses recently erected under his super- 

 intendence : — " The boiler we now use is 

 so constructed and fixed as to become a 

 generator of heat, both by water and air; 

 the fuel, first acting on the bottom of the 

 boiler, passes into the flue surrounding 



it ; the division between the flue and air 

 cavity is built with fire-brick pargeted, 

 and, to prevent the possibility of any 

 escape of smoke or gas, is enclosed in a 

 case of sheet-iron ; the flow of air to the 

 cavity is supplied through a cold air- 

 drain, and, after traversing the cavity and 

 becoming heated, it passes into a chamber 

 formed over the boiler — thus taking up in 

 its passage any heat given out at the top 

 of the boiler before entering the house by 

 the hot-air drain. By the grating we 

 have not only the power of returning the 

 cold air from the house, but also of 

 throwing in a stream of fresh air from 

 outside the house, thus enabling us to 

 keep up a supply of uncontaminated air 

 to the plants, yet with ' the chill off.' We 

 have also the means of circulating the 

 air in the hot chamber, there being a 

 communication with the drain and an 

 outlet by tubes through the plunging- 

 bed. By this means the atmosphere of 

 the house may be kept to any degree of 

 moisture, by evaporation from the troughs 

 which heat the plunging or planting-out 

 materials in the bed." 



§ 4. — THE TANK MODE OF HEATING. 



This method of obtaining bottom heat 

 has of late become very popular, afford- 

 ing uniformity of temperature accom- 

 panied with any degree of humidity the 

 operator desires, without the manual 

 labour attendant on former systems. To 

 those conversant with the history of hor- 

 ticultural improvements, it was by no 

 means unknown, long before Mr Rendle 

 either published his treatise on it or ap- 

 plied it in practice. In stating this, we do 

 it merely as a horticultural statistical fact, 

 of which we believe that gentleman was not 

 aware at the time he published his first 

 account of the system. Circumstances of 

 this kind are not at all uncommon in re- 

 gard to inventions ; for we have known, 

 more than once, two individuals, at the 

 very same period, totally unknown to 

 each other, and, in one case, living in 

 different countries, bringing out identical 

 inventions at the same time. 



The late Mr Smith of Hopetoun House, 

 so long ago as 1832, heated his pine-pits 

 by open tanks or gutters, the water being 

 made to circulate under the beds. 



