74 
MR. T. S. STARTON ON THE PASSAOE OF HEAT BETWEEN 
A satisfactory means of measuring the surface temperature was' found in the 
following way. 
Since the thickness of the metal was only 0'08 centim., and the heat transmitted 
per square centim. per second was not in any case greater than 10 thermal units, 
and in the majority of the experiments was less than 5 thermal units, then, from the 
known conductivity of copper, the fall of temperature from one side of the wall to the 
4. 
other would in most cases be less than 0'5° and would never exceed 1°. Thus, if the 
mean temperature of the pipe be determined, then by applying a small correction to 
this, depending on the amount of heat transmitted, the surface temperature can be 
found. 
The mean temperature of the l)ipe was found by observing the actual elongation of 
the copper pipe by means of an extensometer, the arrangement being shown in fig. 5. 
A is a cast-iron standard, the upper face of which is planed, and into which the 
copper tube is screwed, the connexion being as thin as possible, in order to prevent 
loss of heat from the pipe to the metal of the standard. At a distance of 3^ inches 
