in Chemical Combinations. 489 



it, and caused it to form part of a circuit in which a pile consist- 

 ing of sixteen of the large Daniell's cells in series and the gal- 

 vanometer were placed. The circuit remained closed for exactly 

 five minutes, during which time the deflections of both ends of 

 the pointer of the galvanometer were observed three times. The 

 mean of all the observations, no two of which differed from each 

 other more than a few minutes of a degree, when properly cor- 

 rected for the error in the position of the pointer, was 72° 17'. 

 The increase of the temperature of the water, ascertained with 

 all proper precautions in stirring, &c, was indicated by 81 '8 

 divisions of the scale of the thermometer, each division corre- 

 sponding to y^jth of a degree Cent. The temperature of the 

 room was 2 o, 07 Cent, lower than the mean temperature of the 

 water. 



As soon as the experiment just described was finished, another 

 was performed in exactly the same manner ; only the direction 

 of the current was reversed, in order that the deflections might 

 be observed on the other side of the meridian. 



At 7 o'clock p.m. of the same day, two experiments were again 

 made in the manner above described ; but in these the quantity 

 of electricity passed through the silver wire was only about half 

 as much as before ; five cells of the pile being now employed, 

 instead of sixteen as before. 



On the morning of September 5, two experiments of the same 

 kind were made with a pile consisting of two cells in series; 

 and on the evening of the same day, two experiments were made 

 using only one of the constant cells. 



On the two succeeding days all the above experiments were 

 gone over again in the reverse order, beginning with one cell 

 and ending with sixteen. In this way I sought to get rid of the 

 mischievous effects of any change in the intensity of the earth's 

 magnetism during the experiments. 



The table of these results which I subjoin will easily be un- 

 derstood by means of the headings of the columns ; and the only 

 thing, therefore, which it will be necessary for me to say in ex- 

 planation of it is, that the last column contains the results of 

 observation corrected for the cooling or heating effect of the sur- 

 rounding air. The amount of this correction was estimated by 

 simple and decisive experiments, and was in no one instance 

 found to exceed one-tenth of the quantity of heat evolved, even 

 in the experiments with one cell, in which the heat evolved was 

 least. 



