and the Mode of its Communication. 169 
As the rays emitted by this hot body are sent off in right lines, 
in all directions, in the same manner as light is emitted by lu- 
minous bodies, all those rays which fall on the concave polished 
surface of the mirror A, will be reflected (as is well known) in 
lines nearly parallel to the axis of the mirror ; they will conse- 
quently fall on the concave polished surface of the opposite 
mirror B ; and, being there again reflected, they will be concen- 
trated at the focus of the second mirror. 
If now a sensible thermometer, at the temperature of the 
room, be placed in this focus, it will immediately begin to rise, 
in consequence of the heat generated in it by the action of these 
calorific rays, so accumulated in that place. 
If, instead of being placed in the focqs of this second mirror, 
the thermometer be placed at a very small distance from that 
focus, on one side of it, the instrument, however sensible it may 
be, will not be apparently affected by the rays from the hot 
body. 
This experiment, which is of ancient date, has often been 
made, and always with the same results. 
Let us now suppose the hot body to be removed from the focus 
of the mirror A ; and that a colder body be substituted in place 
of it. And, in the first place, we will suppose the temperature 
of- this colder body to be that of freezing water, or just equal to 
that, which reigns in the room. 
As the rays which bodies at the same temperature send off 
from one to the other, have no tendency to increase, or to di- 
minish, the temperature of those bodies, the concentration of rays 
in the focus of the mirror B, proceeding from the ice-cold body 
placed in the focus of the mirror A, can have no effect on a 
mdccciv. Z 
