474 
NATURE 
[April 13, 1871 

EXAUPLES Of THE PERFORMANCE OF 
THE ELECTRO-MAGNETIC ENGINE * 
See experiments and conclusions I arrived at a 
quarter of a century ago having been recently criti- 
cised, I have thought it might be useful to place the | 
subject of work in connexion with electro-magnetism in a | 
different and I iiope clearer form than that in which I 
have hitherto placed it. The numbers given below are 
derived from recent experiments. 
Suppose an electro-magnetic engine to be furnished 
with fixed permanent steel magnets, and a bar of iron 
made to revolve between the poles of the steel magnets by 
reversing the current in its coil of wire. Such an arrange- 
ment is perhaps the most efficient, as it is the most simple 
form of the apparatus. In considering it, we will first 
suppose the battery to consist of 5 large Daniell’s cells in 
series, so large that their resistance may be neglected. 
We will also suppose that the coil of wire on the revolving 
bar is made of a copper wire 389 feet long, and {34 of an 
inch diameter, or offering a resistance to one BA unit. 
Then, on connecting the terminals of this wire with the 
battery, and keeping the engine still, the current through 
the wire will be such as, with a horizontal force of earth’s 
magnetism 3°678, would be able to deflect the small 
needle of a galvanometer furnished with a single circle of 
one foot diameter, to the angle of 54°23. Also this 
current going through the above wire for one hour will 
evolve heat that could raise 110°65 Ibs. of water 1°, a 
quantity equal to 85430 ft. lbs. of work. In the mcantime 
the zinc consumed in the battery will be 535°25 grains. 
Hence the work due to each grain of zinc is 159°6 ft. lbs., 
and heat ‘20674 of a unit. 
I. In the condition of the engine being kept still we 
have therefore, current being 1°395, as shown by a deflec- 
tion of 54° 23, 
1. Heat evolved per hour by the wire 110°66 units. 
2. Consumpuion of zinc per hour 535°25 grains. 
3. Heat due to 535°25 grains, 110°66 units. 
4. Therefore the work per hour will be (110°66 -- 110°66) 
772=0. 
5. And the work per grain of zinc will be gee? 
II. If the engine be now started and kept by a proper 
load to a velocity which reduces the current to %, or 9307, 
indicated by deflection 42° 57’, we shall have 
1. Heat evolved per hour by the wire 110°66 x ’ Hl = 
4918 units. 
ie) 
. Consumption of zinc per hour 535'25 x = = 
grains. 
bo 
. Heat due to 35683 grains, 110°66 x 5 = 73°77 units. 
4. Therefore the work per hour will be (73°77 — 49°18) 
772 = 18983 ft. Ibs. 
5. And the work per grain of zinc will be oe Se 
: 35683 
or } of the maximum. 
III. If the load be lesssened until the current is reduced 
to > of the original amount, or to ‘698, we shall have 
1. Heat evolved per hour by the wire 110°66 (Gy = 
27°665 units. 
2. Consumption of zinc per hour 535°25 x ; = 267°62 
grains. 
3. Heat due to 267'62 grains 110°66 X < = 55°33. 
: * TF om the Proceedings of the Manchester L'terary and Philosophical 
celety. 

4. Therefore the work per hour will be (55°33 — 27°665) 
772 = 21357. 
5. And the work per grain of zinc will be a 
or 3 of the maximum duty. 
IV. If the load be still further reduced and velocity in- 
creased so as to bring down the cnrrent to }.of what it 
was when the engine was still, or to “4653, shown by a 
deflection of the galvanometer of 24° 57, we shall have 
1. Heat evolved per hour by the wire 110°66 X & y = 
12294 units. 
2. Consumption of zinc per hour 535°25 X : == 178°42 
grains. 4 
3. Heat due to 178°42 grains 110°66 X : = 36°89 units. 
4. Therefore the work per hour will be (36°89 — 12°294) 
772 = 18988 ft. lbs. 
And the work per grain of zinc will be tees =! 
5- pers 17842 
or 3 of the maximum duty. 
V. Remove the load still further until the velocity in- 
creases so much that the current is brought down to ,$o 
of its quantity when the engine is still. Then we shall 
have 
1. Heat evolved per hour by the wire 110°66 X (35) 
100 
= ‘011066 of a unit. 
. Consumption of zinc per hour 535'25 X — = 53525 
to 
grains. 
3. Heat due to 5°3525 grains of zinc 110°66 x= 11066 
units. 
4. Therefore the work per hour will (1°1066 — ‘01 1066)772 
= 845°73 ft. lbs. 
5. And the work per grain of zinc will be 873 = 158 
or ;%% of the maximum duty. 
When the velocity increases so that the current vanishes 
the duty=159°6. 
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 } 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 
a 5°584, shown by a deflection of 79° 51’. Then we shall 
have 
2 
1. Heat evolved per hour by the wire 11065 X c= 
442°64 units. 
2. Consumption of zinc per hour 535°25 X4=2141 grains. 
3. Heat due to 2141 grains 44264 units. 
4. Therefore the work per hour will be (442°64— 44264) 
772=0. 
5. And the work per grain of zinc will be ae 
II. Start the engine with such a load as shall reduce 
the current to 2, or to 3°7227 (74° 58’), then we shall have 
1. Heat evolved per hour by the wire 442°64 x S ¥ ae 
196°73 units. 
te 
. Consumption of zinc per hour 2141 X = 1427°3 
grains, 
3. Heat due to 1427°3 grains 442°64 * — =295’09 units, 
95°C — 196'73) 
Wilh 
4. Therefore the work per hour will be ( 
772 = 75934- 
iS) 
