.IS Steam Engine. 
abutments which rest on the other abutments of the side 
plates when this plate is put into its place ; this plate by 
such means may be taken out, or put in at any time it is 
found necessary, without meddling with any other part of 
the hopper : another method is to have the bottom plate 
to come out, and in the same manner as the regulating 
plate ; also, that it may fold up or down to any inclination ; 
this form is very commodious for allowing access into the 
fire-place to get it repaired, or the like, or for having the 
fire quickly taken from it altogether, for by folding the 
plate to a level as represented by the dotted line, Fig. 9, 
the coal which is in the hopper is prevented from falling 
into the fire-place, and there is a greater space left to get 
into it ; this form may either admit or not of the grated- 
doors ; indeed the simple opening does very well. Fig, 
9, is a representation of the side of the hopper, in this 
form : another method of the hopper, and letting in of air, 
is by making the underside of the top plate with cheeks, 
or grooves, as that the fresh air may rush down in them 
above the fuel that lies in the hopper, for when the hop- 
per is fitted in as close with coal as it can be, these 
grooves or cheeks prevent the coal from getting into them, 
and form separate and definite spaces for the air to rush 
down on the burning fuel, and perform the same office as 
the regulating plate, though the proper quantity cannot be 
so well adjusted this way, yet the only way to accomplish 
this is to have these grooves or cheeks made as near the 
proper size as possible ; they ought also to be so narrow, 
that little of the coal will get betwixt them. Fig. 10, is 
a front view of the hopper, in the state where A represents 
the opening coals are put into ; another method is to let 
in the current of fresh air above the uppermost plate of the 
hopper, this may be done either by another plate placed 
above, or the building so formed over it, as that a proper 
quantity of fresh air may get in, and in a proper direction ; 
