155 
I. Let us now improve the engine by giving it a coil of 4 
times the conductivity, which will be done by using a 
copper wire 389 feet long and £th of an inch diameter, the 
same battery being used as before. Then when the engine 
is kept still we shall have a current 1*396 x 4 = 5*584, 
shown by a deflection of 79° 51'. Then we shall have 
4 2 
1. Heat evolved per hour by the wire 110*66 x - =442*64 units. 
2. Consumption of zinc per hour 535*25 x 4 = 2141 grains. 
3. Heat due to 2141 grains 442*64 units. 
4. Therefore the work per hour will be (442*64 — 442*64)772 = 0. 
5. And the work per grain of zinc will be gpji - 0 
II. Start the engine with such a load as shall reduce the 
current to f, or to 3*7227 (74° 58'), then we shall have 
1. Heatevolvedperhourbythewire442*64 x = 196*73 units. 
2 
2. Consumption of zinc per hour 2141 x - = 1427*3 grains. 
3. Heat due to 1427*3 grains 442*64 x | = 295*09 units. 
4. Therefore the work per hour will be (295*09 -196*73)772 
= 75934. 
5. And the work per grain of zinc*, will be ^ 7-3 ~ ^ *2 or ^ of 
the maximum duty. 
III. Lessen the load so that the velocity of the engine is 
increased until the current is reduced to one half its original 
amount, or 2*792 shown on the galvanometer by a deflec- 
tion of 70° 18'. Then we shall have, 
1. Heatevolved per hour by the wire 442*64 x = 1 10*66 units. 
2. Consumption of zinc per hour 2141 1070*5 grains. 
3. Heat due to 1070*5 grains, 442*64 x - = 221*32 units. 
4. Therefore the work per hour will be (221*32- 110*66)772 
= 85430 ft. lbs. 
85429 
5. And the work per grain of zinc will be = 79*8 or £ the 
maximum duty. 
