426 HENRY A. EOWLAND 



The number of revolutions was determined by a chronograph, which 

 received motion by a screw on the shaft ef, and which made one revo- 

 lution for 102 of the shaft. On this chronograph was recorded the 

 transit of the mercury over the divisions of the thermometer. 



Around the calorimeter a water jacket, tu, made in halves, was 

 placed, so that the radiation could be estimated. A wooden box sur- 

 rounded the whole, to shield the observer from the calorimeter. 



The action of the apparatus is in general as follows: As the inner 

 paddles revolve, the water strikes against the outer paddles, and so 

 tends to turn the calorimeter. When this force is balanced by the 

 weights op, the whole will be in equilibrium, which is rendered stable 

 by the torsion of the wire cd. Should any slight change take place in 

 the velocity, the calorimeter will revolve in one direction or the other 

 until the torsion brings it into equilibrium again. The amount of tor- 

 sion read off on a scale on the edge of Tel gives the correction to be 

 added to or subtracted from the weights op. 



One observer constantly reads the circle Tel, and the other constantly 

 records the transits of the mercury over the divisions of the ther- 

 mometer. 



A series extending over from one half to a whole hour, and record- 

 ing a rise of 15 C. to perhaps 25 C., and in which a record was made 

 for perhaps each tenth of a degree, would thus contain several hundred 

 observations, from any two of which the equivalent of heat could be 

 determined, though they would not all be independent. Such a series 

 would evidently have immense weight; and, in fact, I estimate that, 

 neglecting constant errors, a single series has more weight than all of 

 Joule's experiments of 1849, on water, put together. 44 



The correction for radiation is inversely proportional to the ratio of 

 the rate of work generated to the rate at which the heat is lost; 

 and this for equal ranges of temperature is only 7 V as great in my 

 measures as in Joule's; for Joule's rate of increase was about 0-62 C. 

 per hour, while mine is about 35 C. in the same time, and can be in- 

 creased to over 45 C. per hour. 



3. DETAILS 

 The Calorimeter 



Joule's calorimeter was made in a very simple manner, with few 

 paddles, and without reference to the production of currents to mix 



44 Forty experiments, with an average rise of temperature of 0-56 F., equal to 

 0-31 C., gives a total rise of 12 -4 C., which is only about two-thirds the average of 

 one of my experiments. As my work is measured with equal accuracy, and my 

 radiation with greater, the statement seems to be correct. 



