OF ARTS AND SCIENCES. 175 



quietly for some time, was now attached, and the experiment com- 

 menced. First the weights had to be adjusted >o as to produce equi- 

 librium as nearly as possible. 



The observers then took their positions. One observer constantly 

 recorded the transit of the mercury over the divisions of the ther- 

 mometer, making other suitable marks, so that the divisions could be 

 afterwards recognized. He also read the thermometers giving the 

 temperatures of the air, the bottom of the calorimeter thermometer, 

 and of tlie wheel just above the calorimeter ; and sometimes another, 

 giving that of the cast-iron frame of the instrument. 



The oilier observer read the torsion wheel once every revolution of 

 the chronograph cylinder, recording the time by his watch. He also 

 recorded on the chronograph every five minutes by his watch, and 

 likewise stirred the water in the jacket at intervals, and read its tem- 

 perature. 



The recording of the time was for the purpose of giving the con- 

 necting link between the readings of the torsion circle and of the ther- 

 mometer. This, however, as the readings were quite constant, had 

 only to be done roughly, say to half a minute of time, though the 

 records of time on the chronograph were true to about a second. 



The thermometers to read the temperature of the water in the 

 jacket were graduated to 0°.2 C, but were generally read to 0°.l C, 

 and had been compared with the standards. There was no object in 

 using more delicate thermometers. 



After the experiment had continued long enough, the engine was 

 stopped and a radiation experiment begun. The last operation was 

 to weigh i he calorimeter again, after removing the thermometer and 

 safety-tube, and also the weights which had been used. 



The chronograph sheet, having then been removed from the cylin- 

 der, had the time records identified and marked, as well as the ther- 

 mometer records. Each line of the chronograph record was then 

 numbered arbitrarily, and a table made indicating the stand of the 

 thermometer and the number of the revolutions and fractions of a 

 revolution as recorded on the chronograph sheet. The times at which 

 these temperatures were reached was also found by interpolation, and 

 recorded in another column. 



From the column of times the readings of the torsion circle could 

 be identified, and so all the necessary data would be at hand for cal- 

 culating the work required to raise the temperature of one kilo- 

 gramme of the water from the first recorded temperature to any 

 succeeding temperature. 



