FOR DETERMINING THE RADIATING POWERS OF SURFACES IN AIR. 383 
3. In the accompanying diagrams A is a cylindrical tin vessel, of which A' represents 
a vertical section through its axis. Its top is shghtly conical, and has an orifice at its 
centre to admit the insertion of a thermometer; and its bottom is slightly curved as 
represented in the section, leaving a space hcdsr through which the radiation takes 
place fi’om the heated surface in the position r s. The conical form of the top facilitates 
the drying of the vessel after it has been immersed in water to obtain a particular 
uniform temperature. The section also represents the thermometer used to ascertain 
the temperature of the distilled water with which the vessel is filled when the experi- 
ments are made with it. It is of the form of the letter L, the horizontal part being the 
bulb. The stem passes through a hole in the cork (a) which fits the central orifice, and 
