Dynamo-machine and Lamp. 477 
the machine. The total energy of course includes that which 
is uselessly spent in heating the coils of the armature itself, a 
very small portion in this form of machine. Our results are as 
follows 
On March 19th the experiment lasted five minutes. We 
ound: 
Energy expended in driving armature -_ - “i 1,500 ft. ibs. 
Energy expended on field of force _ .. .--- 16,400 
Bote ciw da wiet el O87, 000.4 
The current calculated from the amount of copper deposited 
was 34335 webers: the mean resistance of the circuit was 3°12 
ohms, or, exciuding the armature, 2°98 ohms. The electromo- 
tive force, indicated by the galvanometer, was 102°36 volts. 
From these data we calculate: 
Total energy realized in the current ..... 814 an ft. Ibs. 
Available energy (excluding sania) ey 4 7,2 “i 
Hence the total oe is 82°3 per cent, and re available 
efficiency 78-7 per cent. 
On April 8rd the first test lasted 18" 50%, and we found— 
Energy expended in driving armature _. 2,844,600 ft. Ibs. 
Energy expended on field ....--...-.-. 1 2 
rection. 
The resistance of the coil in the calorimeter was 1°72 ohms; 
that of the leading wires was only about 0-006, or gs}, of the 
preceding. Hence assuming 772 ft. lbs. as the mechanical 
equivalent of heat we have— 
Energy developed in calorimeter------. - 2,227,500 ft. Ibs. 
Energy developed in seo wires ..---- 7,425 “ 
Energy developed in armature......-.-- 183,670 “ 
That is to say : 
Total energy reali 2,418,600 
Available energy ae es dips veo 2,234,925 “ 
which makes the total —— 84°6 per cent and the avail- 
able efficiency 78°2 per 
Am. Jour. Sc1.—THIRD Sexi Hox: XIX, No. 114.—Jung, 1880, 
