838 
3rR. W. HOPKIXS’S EXPEEBIEXTAL EESEAECHES 
the stove, the walls and roof of which are of cast u'on. The horizontal section of it below 
the roof is rectangular ; the orifice at the top is circular. C is the commencement of the 
chimney, which is carried horizontally and then vertically through the roof of the building, 
the horizontal portion being sufficiently long to prevent any sensible influence on the expe- 
riments arising from the heat radiating from the chimney. In the side of the stove is 
a rectangular opening D, which may be closed at pleasure, and through which fuel is 
supplied to the grate G. This grate fits the stove, but so as to be capable of mo’sing 
freely up and down within it. The opening in the lower part of the stove at O is large 
enough to admit of the grate and the fuel contained in it being withdrawn entirely 
from the stove when required. 
The horizontal section of the upper portion of the vessel V is rectangular ; that of the 
part projecting downwards is circular, and such as to pass freely into the circular orifice 
at the top of the furnace, to the roof of which also this vessel is made to fit. MX is a 
shallow vessel, just fitting the top of V, on the upper rim of which it is supported by 
the projecting edges represented at M and N, when the parts are put together as 
in fig. 6. L there represents a lever working on a fulcrum at O, and so attached 
to the grate at the ends of an axis H, perpendicular to the plane of the paper, as to 
constitute a rough approximation to a parallel motion when the grate is moved vertically 
by heightening or lowering the opposite extremity of the lever, to which a coimter- 
balancing weight is suspended. The lever, also, is easily removeable from the ful- 
crum O, and then becomes a handle by which the grate and its contents can be entii'ely 
withdrawn from the stove as above stated. Thus by raising or lowering, or by partially 
or entirely withdrawing the fire, the heat communicated to the vessel Y can be regulated 
with considerable nicety as circumstances may requu’e. A chimney, proceeding to a 
sufficient distance horizontally from the vessel V, carries off" the steam when water is 
used in V at the boiling temperature. 
Fig. 7 represents one of the blocks, of which I had 
several of different thicknesses, and made of sub- 
stances of different conductive powers. Its horizontal 
dimensions are such as to fit easily into the shallow 
vessel MN. In the centre of the block is a cylin- 
drical orifice, five inches in diameter, for the recep- 
tion of cylinders of any substance the conducti-s’e 
power of which is to be determined. In making an experiment, a sufficient quantity 
of mercury is poured into the shallow vessel MN, just to cover six points projecting 
from its bottom. The large block is then placed so as to rest on three of these points, 
and the inner cylindrical block to be experimented on is then inserted m the cylindrical 
orifice of the large block, and rests on the other three projecting pomts. The exact 
contact of the lower surfaces of both blocks with the mercury is thus secured. The 
outer block is also surrounded by a square frame of wood, ufithout top or bottom, rest- 
ing on the rim of the vessel V. The apertures between this frame and the sides of the 
