452 Messrs. Scoresby and Joule on the Mechanical 



and the actual duty, 



1™«5 = 9S-8. 

 190 



Taking the mean of the two experiments, we have for the 

 theoretical duty 95-3, and for the actual performance 98*3. 

 Here, therefore, in apparent contradiction to what we have 

 just said, the actual exceeds the theoretical duty. This cir- 

 cumstance is however partly explained by the fact that the 

 solution of sulphuric acid employed in charging the battery 

 had been mixed immediately before the experiments were 

 made, and was in consequence considerably heated; for 

 Daniell has shown that the intensity of his battery increases 

 with its temperature, and it is evident that an increase of the 

 intensity or electromotive force of the cells of the battery must 

 be productive of an increased ceconomical effect. 



The next two experiments were made with the hollow re- 

 volving armature, its two coils being arranged for quantity. 

 In these and the subsequent experiments, the battery was 

 charged with a cold solution. 



Experiment 3. — Current when the engine was kept at rest, 

 1381 ; current when the armature was revolving 80 times per 

 minute, 850; consumption of zinc, 190 grains per hour; 

 power developed, 8800 lbs. raised a foot high per hour. From 

 these data, the theoretical duty will be 



158(1381-850) 



FssT = 60 7 ' 



and the actual duty will be 



^° = "** * 



190 

 Experiment 4. — Current before the engine was allowed to 

 start, 1381 ; current when the engine was revolving 102 times 

 per minute, 678; consumption of zinc, 151 grains per hour; 

 power developed, 9000 lbs. raised a foot per hour. Hence 

 for the theoretical duty we have, 



158(1381 -678) 



1381 

 and for the actual duty, 



9000 



== 80'4, 



= 59'6. 



151 



Lastly, we made two experiments in which the engine was 

 fitted up with two straight electro-magnets fastened parallel 

 to the axis. Each of these straight electro-magnets consisted 

 of a piece of drawn iron tube, 12 inches long, l|th inch in 



