253 GARDEN MANAGEMENT. 



ho'aily, and 200 cubic feet of air are heated l" per minute by every foot of 

 4-inch pipe : it is easy, by cubing the contents of the building to be heated, 

 and dividing it by 200, to calculate the quantity of pipe required to heat the 

 building to the required temperature. When the required temperature is 60'', 

 the divisor should be 30 ; where it is to be 75° or 80°, 20 will be nearer ; making 

 allowance always for loss by ventilation, and the radiating power of glass, which 

 is about one degree for eveiy square foot and a half, and bearing in mind also 

 that where smaller pipes are used, the body of water is smaller, and, conse- 

 quently, the friction greater ; for instance, in 2-inch pipes the difference of 

 temperature between the flow and return-pipe will be four times greater than in 

 a 4-inch pipe. In order to increase the rapidity of circulation, and equalize the 

 temperature, Mr. Rogers proposes, when 2- or 3-inch pipes are used, that they 

 should have a uniform rise of an inch in 20 feet, while in 4-inch pipes they 

 should fall from the boiler in exactly the same proportion ; for the velocity of 

 circulation depends upon the difference in weight between the ascending and 

 descending columns. Now the gi-eater the height of these columns, the greater is 

 the difference in their weight and in the velocity of circulation, and the higher 

 the mean temperature of the pipes. 



699. The inventor, or rather discoverer of the theory of the circulation of 

 hot water, M. Bonneman, of Paris, had a caloriftre so regulated that he could 

 maintain a temperatiire scarcely varying half a degree of Reaumur, being regu- 

 lated by the unequal dilation of metals. A rod of iron, screwed to another of 

 brass, was inclosed in a lead tube terminating at its upper end in a ring of 

 brass ; the leaden tube was passed through the water in the boiler, by the side 

 of one of the circulating pipes, and the dilation of the lead being greater than 

 that of the iron, and the rod being inclosed within the lead, it was less heated ; 

 and the consequent lengthening of the leaden tube brought the brass ring into 

 contact with a claw at the short end of a bent lever ; the slightest increase of 

 heat lengthened the tube, and pressed down the long end of the lever, and a 

 wire connected with it opened or closed a valve, regulating the air admitted to 

 thefiu-nace; this, however, is a refinement on heating which is rarely prac- 

 tised or required. 



700. Warming by steam is more expensive than by any other process, and 

 rarely practised except in manufactories where it is u^ed as a motive power. 



701. The first successful attempt to introduce warming by means of hot 

 water in this country seems to have been made by Atkinson.^ His idea is 

 founded on the theory of fluids finding their level ; for his first apparatus was 

 merely a boiler, from which the water was made to flow and return by means 

 of two pipes on a perfect level. At the extremity of the pipes a reservoir was 

 considered necessary', exactly on a level with the top of the boiler, the reser- 

 voir being covered with an iron top, fitting into it with a flange ; the boiler 

 with a wooden one. Mr. Atkinson afterwards constructed boilers with closed 

 tops ; by which means he carried hot water 30 feet above the level of the 

 boiler. An improvement upon this system of heating was attempted upon 

 l^hat was called the siphon principle. In an open boiler, the flow-pipe being 



