7 
The first difficulty which has to be encountered here, is the 
very great rapidity with which the power diminishes through 
space. An electro-magnet which will sustain 220 pounds 
when the armature is in contact with its poles, exerts an 
attractive force of 4 0-4- pounds when the armature is at a 
distance of one fiftieth of an inch only. Now you will per- 
ceive that under any of the arrangements which have been 
adopted the moving and the fixed magnets could not be 
brought nearer together than the fiftieth of an inch ; hence 
there is an immediate loss of one fifth part of the power we 
have produced. 
The second difficidty to which I had the satisfaction of first 
directing attention in this country, although I have since been 
informed that it had been detected by Jacobi, is, that the moment 
the magnets begin to move there is a temporary loss of power, 
or, perhaps it would be more correct to say, there is a develop- 
ment of an opposing force, by which the mechanical power is 
again considerably diminished, and the greater the speed with 
which the magnets move, the more rapidly does this decline. 
The report made by order of the American government on 
Professor Page’s electro-magnetic engine directs attention to 
this fact, which the reporting engineers w r ere not able to explain. 
Mr. Hjorth, the most recent inventor and patentee of electro- 
magnetic engines, after the publication of my paper, observed 
the influence of these induced currents, and with a view to 
economy endeavoured to employ them in effecting the precipit- 
ation of the zinc, from the sulphate of zinc formed in the voltaic 
battery employed, but without success. Such are the difficulties 
which at present stand in the way of applying electricity as a 
motive power. It may bo said, that these resolve themselves 
into questions of economy. Granted. The whole of this question 
I have investigated with the closest care, and the result is, that 
a grain of coal consumed in the boiler of a Cornish steam engine 
will lift 143 pounds one foot high, whereas one grain of zinc 
consumed in the voltaic battery will lift but 80 pounds through 
the same space. Now the cost of zinc is 2 1 6c/. per cwt., while 
the cost of coal is but 9 d. per cwt. It will be my duty to show 
and explain early in the present course of lectures that the 
