On radiation, absorption, &c. 325 
disks, and the whole dipping into a vessel, mn, of boiling water. 
The mercury is so small in bulk, that the influence of this strikes the 
student immediately ; but the idea which he thus catches at, is refu- 
ted by the more tardy heating of the water, which is less in bulk 
than the alcohol. 
Before the forms of illustration, of the radi- — 
ation and absorption of heat, already described, 
had suggested themselves, I had contrived 
another apparatus, which gave very good re- 
sults, and may be, by some, preferred to the 
one already described. A long box, abcd 
%, of tin, was divided into compartments by ; & 
partitions, e f, g h, ik, &c., and a top sol- @ poms n 3 
dered upon each, having a conical opening, | 
i, m,n, &c., to receive acork, through which ¢ © g i d 
a tube, op,nr,ms, lt, &c. passed; these compartments were 
made as nearly equal as possible, and the tubes entering them were 
selected of as nearly equal bore as possible ; equal measures of co- 
lored water were poured through the conical openings into the sev- 
eral compartments, so as to cover the bottom to a depth regulated 
as will be presently stated. The tubes and corks were now inser- 
ted, and cemented ; and each cell thus formed an air thermometer, 
the expansion of the air within driving the colored liquid up the tube 
entering the cell. That there might be no error from a want of 
equality in these thermometers, after bringing the liquid to a con- 
venient height in each of the stems, by forcing air into each, or by 
dropping liquid from a dropping tube into the tube; the whole was 
plunged into a vessel of water, of a temperature sufficiently above 
the original temperature of the air within, to give distances on the 
tubes, readily divisible into equal parts of sufficient magnitude. 
ese degrees were marked by a rude scale, formed by colored 
threads, tied around the tubes. One surface of the box was kept 
uniformly bright, or regularly tarnished, or coated; the other a d, 
was coated with substances of different radiating powers. 
The box being placed with the uncoated side towards a vessel of 
warm water, the heat enters uniformly that side of the compartments, 
but is radiated differently from the opposite side, and the liquid from 
the air thermometers is urged more rapidly up those tubes which 
enter into the compartments radiating worst, and ultimately arrives 
ata greater height, showing a greater stationary temperature, or 
€ UJ 
