436 HENEY A. EOWLAND 



The conduction through the vulcanite only amounts to -0000002. 



From this it would seem that three-fourths of the loss is due to 

 radiation and convection combined. 



The last two losses depend upon the difference of temperature be- 

 tween the calorimeter and the jacket, but the first two upon the differ- 

 ence between the calorimeter and frame of the machine and the wheel 

 respectively. The frame was always of very nearly the same tempera- 

 ture as the water jacket, but the wheel was usually slightly above it. 

 At first its temperature was noted by a thermometer, and the loss to 

 it computed separately; but it was found to be unnecessary, and finally 

 the whole was assumed to be a function of the temperature of the 

 calorimeter and of the jacket only. 



At first sight it might seem that there was a source of error in 

 having a journal so near the bottom of the calorimeter, and joined to 

 it by a shaft. But if we consider it a moment, we shall see that the 

 error is inappreciable; for even if there was friction enough in the 

 journal to heat it as fast as the calorimeter, it would decrease the 

 radiation only seven per cent, or make an average error in the experi- 

 ment of only 1 in 700. But, in fact, the journal was very perfectly 

 made, and there was no strain on it to produce friction; besides which, 

 it was connected to a large mass of cast-iron which was attached to 

 the base. Hence, as a matter of fact, the journal was not appreciably 

 warmer after running than before, although tested by a thermometer. 

 The difference could not have been more than a degree or so at most. 



The warming of the wheel by conduction and of the journal by fric- 

 tion would tend to neutralize each other, as the wheel would be warmer 

 and the journal cooler during the radiation experiment than the fric- 

 tion experiment. 



The usual method of obtaining the coefficient of radiation would be 

 to stop the engine while the calorimeter was hot, and observe the 

 cooling, stirring the water occasionally when the temperature was read. 

 This method I used at first, reading the temperature at intervals of 

 about a half to a whole hour. But on thinking the matter over, it 

 became apparent that the coefficient found in this way would be too 

 small, especially at small differences of temperature; for the layer 

 next to the outside would be cooled lower than the mean temperature, 

 and the heat could only get to the outside by conduction through the 

 water or by convection currents. 



Hence I arranged the engine so as to run the paddles very slowly, 

 so as to stir the water constantly, taking account of the number of 



