Mechanical Science, 139 



lever which opens the type inside, the coals slide down on to the 

 fore end of the grate bars, which is only the work of a moment. 

 It is evident that no quantity of cold air can thus get into the 

 furnace ; in fact, it is not possible for any person that does 

 not see the operation of firing, to know when fresh fuel is added 

 by looking at the top of the chimney. The smoke tliat issues is 

 never more than a light grey, just perceptible, but in a general 

 way is not seen at all." 



The coals last admitted are allowed to lie until partially coked, 

 and just before a fresh supply is admitted, are pushed farther 

 along the grate by a tool for the purpose, which remains con- 

 stantly in the furnace : it is merely a plate of iron, about four 

 inches broad, and as long as the grate is wide : it has a handle 

 long enough to be used with both hands, which comes through a 

 hole in the bottom of the door : when not in use it is drawn close 

 up to the door. There is also another hole about one inch in 

 diameter in the fire-door to look through ; a circular piece of iron 

 hangs before it by a loose rivet. 



The certificates of persons who have witnessed the effect of 

 this application speak to its entire success. Those who, previous 

 to the erection of the engine, apprehended a nuisance, have been 

 agreeably disappointed, smoke being seldom seen. On the ap- 

 plication of fresh fuel, the smoke assumed the appearance of a 

 light-grey vapour, which in a few seconds became almost in- 

 visible. On opening the fire-door in the usual way, dense black 

 clouds of smoke rolled out of the chimney, but tliey ceased on 

 closing the door again. An unlooked-for advantage also is, that 

 the grate-bars appear to last longer when thus constructed. — 

 Trans. Soc. Arts, xlii. 32. 



9. Graphical trisection of an Angle. — The following instrument, 

 for such it is, is supposed to be new, and may prove useful to 

 artificers and others who have occasion to trisect any angle. 



C 



K 



H 



