o3a 



THE PRACTICAL GARDENER. 



fire-Hue into the air-flue, as it travels along. None of it comes 

 from the furnace. I had," he says, " a suspicion of these 

 truths, and, in order to put them to the test, had tubes of 

 various shapes, sizes, and lengths made, and which I could 

 lay on the fire-flue, on the ground, or on a shelf, or, in short, 

 any where I pleased. They were all fitted to the air-chamber 

 formed round the furnace, whicli had a turning valve in front, 

 three inches in diameter. That, with which most of the experi- 

 ments were made, was a square tube of three inches wide 

 formed of milled clay, and baked in the same way that garden- 

 pots are. It was of lengths of three feet each, and joined 

 with cement. I tried its efibcts in conducting the heated air 

 from the furnace, at various lengths and at various heights ; 

 from two yards in length to forty feet, and from one foot above 

 the level of the furnace to ten. The result of the whole 

 amounted to this : that, unless when on the top of the fire-flue, 

 air perceptibly hot, could not be drawn from the furnace, to a 

 distance of more than twelve feet, even although the furnace 

 was made ever so hot. When the tube was shortened to two 

 Vnirths (six feet), the air issuing from it raised tlie mercury in 

 tnc thermometer to 120^; but when another length was put on, 

 though the fire was kept equally brisk, it fell to 96° ; and, by 

 adding a fourth length, (the tube being now twelve feet long,) 

 the mercury was not affected by the air of the tube, but fell 

 to the air of the house. The above experiment was made at 

 six feet above the level of the top of the furnace. It was tried 

 at two feet above it with hardly any variation ; but, when laid on 

 the ground, on the same level with the top of the furnace, 

 the heat did not travel to the length of nine feet, so as to 

 affect the spirits in the thermometer." 



FURNACE. 



The furnace recommended by Mr. Atkinson is the best, and 

 has now been very generally in use for upwards of thirty years, 

 and is nearly similar to that recommended by Nicol, and is of 

 a size capable of containing less or more fuel, according to 

 circumstances. The most usual size is thirty inches long, 

 twenty high, and ten broad. The door of this furnace is ten 



