Houses and other Buildings. 235 



falling through tlie height of the tunnel ; and v = the velocity 

 of the ascending air. 



Then r — V x . This equally applies to chimneys, 



d being the density of the smoke. 



The mere exposure of the heated surface in an open space, 

 such as a small room, is not sufficient to produce the greatest 

 effect. This is, however, the method at present used by 

 sugar-bakers for heating the rooms in which they expose their 

 sugars. The vessel so employed is of cast iron, and is called 

 a cockle. 



Various modifications of this method of heating air have 

 been employed. The wall surrounding the heated vessel has 

 been placed at various distances, in order to find the maximum 

 of effect of a given fire. It was considered a great improve- 

 ment, to place the wall at a distance, to admit of a sufficient 

 quantity of air, and make a number of apertures in the wall, 

 about two and a half inches square, with a view to compel the 

 air to blow upon the heated surface. This method was em- 

 ployed more than thirty years ago, by William Strutt, Esq., of 

 Derby, in his cotton-works. He afterwards made a great 

 improvement on this plan, by inserting tubes in the apertures 

 in the wall reaching near to the heated surface. By these means, 

 the air is prevented from ascending before it comes in contact 

 with the heated surface. A further improvement was made in 

 this apparatus, by inserting similar tubes over the surface of 

 the cockle, the shape of which was a square prism with a 

 groined top. The cold air was made to pass through one half 

 of the tubes ; and the air so heated, became still more heated 

 by being compelled to pass in a contrary order through the 

 other half, into a chamber above, called the air-chamber. The 

 stove, thus improved, has been employed by Messrs. Strutts 

 in their works ever since, with complete success, and is simi- 

 lar to that by which the Derbyshire General Infirmary is 

 warmed This stove has been fixed in different parts of the 

 country and in London, sometimes with success ; but so many 

 circumstances besides the stove itself interfere, in arrange- 



