392 HENRY A. EOWLAND 



were made with both thermometers in the calorimeter during the whole 

 experiment. 



The principal sources of error are as follows : 



1st. Thermometers lag behind their true reading. This was not 

 noticed, and would probably be greater in thermometers with very fine 

 stems like Geissler's. At any rate, it was almost eliminated in the 

 experiment by using two thermometers. 



2d. The water may be changed in temperature in passing through 

 the spout. This was eliminated by allowing the water to run some 

 time before it went into the calorimeter. The spout being very thin, 

 and made of vulcanite, covered on the outside with cloth, it is not 

 thought that there was any appreciable error. It will be discussed 

 more at length below, and an experiment given to prove this. 



3d. The top of the calorimeter not being in contact with the water, 

 its temperature may be uncertain. To eliminate this, the calorimeter 

 was often at the temperature of the air to commence with. Also the 

 water was sometimes violently agitated just before taking the final 

 reading, previous to letting in the cold water. Even if the tempera- 

 ture of this part was taken as that of the air, the error would scarcely 

 ever be of sufficient importance to vitiate the conclusions. 



4th. The specific heat of copper changes with the temperature. 

 Unimportant. 



5th. Some water might remain in the spout whose temperature might 

 be different from the rest. This was guarded against. 



6th. Evaporation. Impossible, as the calorimeter was closed. 



7th. The introduction of cold water may cause dew to be deposited on 

 the calorimeter. The experiments were rejected where this occurred. 



The corrections for the protruding thermometer stem, for radiation, 

 &c., were made as usual, the radiation being estimated by a series of 

 observations before and after the experiment, as is usual in determin- 

 ing the specific heat of solids. 



June 14, 1878. First Experiment 

 Time. Ther. 6163. Ther. 6166. Points. 



41 296-75 6163, 57-9 Air, 21 C. 



42 296-7 6165, 34-8 Jacket about 25 C. 



43 296-7 6166, 20-5* 



44 296-65 



