518 REPORT— 1867. 



The correction to be applied to the thermometer immersed in air as de- 



A A i- .V, 1, rr VI • • T, 123-66-12T 3.56-65 + 18.r , 

 duced from the above Table is given by = , whence 



.r= — 1-1835. It appears also that a difference beween the temperatures of 



the calorimeter and air-registering thermometer so corrected, equal to 10-822, 



gives the unit effect on the former. 



Hence the corrected indication of the air-thermometer in the second series 



of thermal experiments will be 349-63-l-1835=348-4465. This being 



12-5345 in excess of the temperature of the calorimeter, the corrected 



12-534.5 

 thermal effect will be 25-65— ^1-4— -=24-4917, which, after a smaU further 



lu-y22 



correction for the immersed stem, becomes 24-512. 



The thermal capacity in this second series was made up of 95561 grains 

 distiUed water, copper as water 2501, thermometer and coil as water 80, 

 and cotton-wool as water 200 grs., giving a total of 98342 grains. 



The equivalent, as deduced from the second series, is therefore 



j -62723 g.gggg I ' -292946 x 33434330 x 3600 

 ( 6-2832 ) 



=25366. 



?i:^X 98342 

 12-951 



The equivalents obtained in the two foregoing series of experiments are 

 as much as one-fiftieth in excess of the equivalent I obtained in 1849 by 

 agitating water. I therefore instituted a strict inquiry with a view to 

 discover any causes of error, so that they might be avoided in a fresh series. 

 The most probable source of error seemed to be insuificient stirring of the 

 water of the calorimeter. Although agitated so frequently as forty times in 

 the hour, there could be no doubt that, during any intervals of comparative 

 rest, a current of heated water would ascend from the coil, and that if a thin 

 stratum of it remained any time at the top, some loss of heat would result. 

 I resolved therefore to use a fresh calorimeter, and to introduce into it a 

 stirrer which could bo kept in constant motion by clockwork. 



Another source of error which, though it would be finally eliminated by 

 frequent repetition of the experiments, it seemed to be desirable to avoid, 

 was the hygrometric quality of the cotton-wool which enveloped the calori- 

 meter in the second series of experiments. I therefore sought for a material 

 which did not present that inconvenience. The plan finally adopted was to 

 cover the calorimeter first with tinfoil, to place over that two layers of silk 

 net (tuUe), and to finish with a second envelope of tinfoil. 



A third source of possible error was the circumstance that the silver- 

 platinum alloy, when made positively electrical in distilled water, is slowly 

 acted upon, an oxide of silver as a bluish-white cloud aiising from the metal, 

 while hydrogen escapes from the negative electrode. On this account the 

 coil in the experiments of the last series, as well as the subsequent, was well 

 varnished. But it was found at the conclusion of the experiments that the 

 varnish had in a great measure lost its protecting power. This circumstance 

 gave me considerable anxiety : I was, however, ultimately able, by the fol- 

 lowing facts arrived at after the thermal experiments were completed, to 

 satisfy myself that no perceptible influence had been produced by it on the 

 results : — 



1st. The resistance of the coils, after long-continued use had deteriorated 

 the varnish, was not sensibly less than it was after they had been freshly 

 varnished. 



