384 ME. W. HOPKIXS OX THE COXSTEUCTIOX OF A XEW CALOEDIETEE 
a small piece of cork is fastened on the heel of the instrument at c, on which the ther- 
mometer can be freely turned by the finger and thumb applied to the upper extremity 
of the stem. The horizontal bulb then becomes a most efiectire stirrer during the 
experiments, by maintaining it in constant rotation about 
the centre c. The thermometer is extremely dehcate, 
each graduation of about y-th of an inch corresponding 
to i^th of a degree of Fahrenheit. It was easy, there- 
fore, by the aid of a lens, to read to the hundredth part 
of a degree. 
The diagram B represents a wooden rim ef^ of which 
the inner diameter is about half an inch larger than the 
diameter of the vessel A, so that the vessel can pass 
freely within it. Three wires are firmly fixed into the 
upper surface of the rim, and to the block g. AMien 
the instrument is put together, the vessel A is placed 
concentrically within the rim, in which it is firmly sup- 
ported by three small wooden wedges between itself and 
the rim, and so that the circumference of the cucular 
bottom of A may be exactly level with the lower surface 
of the rim ef. Also the thermometer being inserted 
through a and the orifice corked, the upper part of the 
stem passes through a central hole in the small wooden 
block g. The calorimeter thus put together is repre- 
sented by the diagram E. The upright uires form at 
once a protection to the thermometer, and a convenient 
means of handling the instrument without touching the 
vessel containing the distilled water. 
4. In performing an experiment, the substance whose 
radiating power has to be determined is formed into a thm disc, the diameter of which 
is such as just to allow it to fit freely into an iron cylindrical vessel represented by E 
which contains such a quantity of mercury that the disc floating upon it shall liaAe its 
upper surface exactly on a level with the rim of the cylinder. The required tempe- 
rature is then given to the disc by heating the mercury on wliich it rests. This is 
effected, as represented in the diagram F, by placing the iron cylinder on the thin iron 
