weight of the damper is so adjusted, that it will only balance the float P when 

 the latter rests on the surface of the water. 



Whenever the evaporation of the boiler is insufficient, it is evident from what 

 has been stated, that the float P will fall and the damper will rise, and will af- 

 ford a greater passage for air through the flue. This will stimulate the furnace, 

 will augment its heating power, and will therefore increase the rate of evapo- 

 ration in the boiler. If, on the other hand, the production of steam in the 

 boiler be more than is requisite for the supply of the engine, the float will be 

 raised and the damper let down, so as to contract the flue, to diminish the 

 draught, to mitigate the fire, and therefore to check the evaporation. In this 

 way the excess, or defect, of evaporation in the boiler is made to act upon the 

 fire, so as to render the heat proceeding from the combustion as nearly as pos- 

 sible proportional to the wants of the engine. 



The method of feeding the furnace by hand through the fire-door being sub- 

 ject to the double objection of admitting more cold air over the fuel than is 

 necessary for its combustion, and the impracticability of insuring that regular 

 attendance on the part of the stokers, directed the attention of engineers to 

 the construction of self-regulating furnaces. The most effectual of these, and 

 that which has come into most general use, was invented by Mr. William 

 Brunton, of Birmingham. 



The advantages proposed to be attained by him were those expressed in his 

 patent : 



il 1 . I put the coal upon the grate by small quantities, and at very short in- 

 tervals, say every two or three seconds. 2. I so dispose of the coals upon 

 the grate, that the smoke evolved must pass over that part of the grate upon 

 which the coal is in full combustion, and is thereby consumed. 3. As the in- 

 troduction of coal is uniform in short spaces of time, the introduction of air is 

 also uniform, and requires no attention from the fireman. 



" As it respects economy : 1. The coal is put upon the fire by an appara- 

 tus driven by the engine, and so contrived that the quantity of coal is propor- 

 tioned to the quantity of work which the engine is performing ; and the quan- 

 tity of air admitted to consume the smoke is regulated in the same manner. 

 2. The fire-door is never opened, excepting to clean the fire ; the boiler, of 

 course, is not exposed to that continual irregularity of temperature which is 

 unavoidable in the common furnace, and which is found exceedingly injurious 

 to boilers. 3. The only attention required is to fill the coal-receiver every 

 two or three hours, and clean the fire when necessary. 4. The coal is more 

 completely consumed than by the common furnace, as all the effect of what 

 is termed * stirring up the fire' (by which no inconsiderable quantity of coal 

 is passed into the ash-pit), is attained without moving the coal upon the 

 grate." 



A circular grate is placed on a vertical revolving shaft ; on the lower part of 



this shaft, under the ash-pit, is placed a toothed wheel driven by a pinion. 



This pinion is placed on another vertical shaft, which ascends above the 



boiler ; and on the other end of this is placed a bevelled wheel driven by a 



pinion. This pinion is attached to a shaft, which takes its motion from the 



axis of the fly-wheel, or any other revolving shaft connected with the engine. 



A constant motion of revolution is therefore imparted to the circular grate, and 



its velocity being proportional to that of the engine, will necessarily be also 



proportional to the quantity of fuel which ought to be consumed. Through 



I that part of the boiler which is over the fire-grate a vertical tube or opening is 



> made directly over that part of the furnace which is most distant from the flues. 



| Over this opening a hopper is placed, which contains the fuel by which the 



1 boiler is to be fed ; and in the bottom of this hopper is a sliding- valve, capable 



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