PRESIDENTIAL ADDRESS. 613 
thirty years ago.’ After explaining the elementary principles of electro- 
magnetism, he describes the early motors of Dal Negro, Jacobi, Davenport, 
Davidson, Page, and others. Reviewing these and their non-success as com- 
mercial machines, he says: ‘Notwithstanding these numerous trials... it 
does not appear that any satisfactory explanation has ever been given of the 
causes which have led to the abandonment of the idea of employing electricity as 
a motive power. It is mainly with the view of directing attention to these 
causes that the present communication has been written.’ He admits that 
electromagnets may be constructed to give any desired lifting power; but he 
finds that the attractive force on the iron keeper of a magnet of his own, which 
held 220 lb. when in contact, fell to 36 1b. when the distance apart was only 
one-fiftieth of an inch. To this rapid falling off of force, and to the hardening 
action on the iron of the repeated vibrations due to the mechanical concussion of 
the keeper, he attributed the small power of the apparatus. Also he remarked upon 
the diminution of the current which is observed to flow from the battery when the 
motor was running (which Jacobi had, in his memoir on the theory, traced to a 
counter electromotive force generated in the motor itself), and which reduced the 
effort exerted by the electromagnets ; this diminution he regarded as impairing the 
efficiency of the machine. ‘All electromagnetic arrangements,’ he says, ‘ suffer 
from the cause named, a reduction of the mechanical value of the prime mover, in 
a manner which has no resemblance to any of the effects due to heat regarded as 
a motive power.’ Proceeding to discuss the batteries he remarked that as animal 
power depends on food, and steam power on coal, so electric power depends on 
the amount of zinc consumed; in support of which proposition he cited the 
experiments of Joule. He gives as his own results that for every grain of zinc 
consumed in the battery his motor performed a duty equivalent to lifting 86 lb. 
one foot high. Joule and Scoresby, using Daniell’s cells, had found the duty to 
be equivalent to raising 80 lb. ove foot high, being about half the theoretical 
maximum duty for one grain of zinc. In the Cornish engine, doing its best duty, 
one grain of coal was equivalent to a duty of raising 143 lb. one foot high. He put 
the price of zinc at 35/, per ton as compared with coal at less than 1/. per ton, 
which makes the cost of power produced by an electric motor—if computed by 
the consumption of zinc in a battery—about sixty times as great as that of an 
equal power produced by a steam-engine consuming coal. He concludes that ‘ it 
would be far more economical to burn zine under a boiler and to use it for gene- 
rating steam power than to consume zinc in a battery for generating electro- 
magnetical power.’ 
In the discussion which followed, several men of distinction took part. 
Professor William Thomson, of Glasgow (Lord Kelvin), wrote, referring to the 
results of Joule and Scoresby: ‘These facts were of the highest importance in 
estimating the applicability of electromagnetism, as a motive power, in practice ; 
and, indeed, the researches alluded to rendered the theory of the duty of electro- 
magnetic engines as complete as that of the duty of waterwheels was generally 
admitted to be. Among other conclusions which might be drawn from these 
experiments was this: that, until some mode of producing electricity as many 
times cheaper than that of an ordinary galvanic battery as coal was cheaper than 
zinc, electromagnetic engines could not supersede the steam-engine.’ Mr. W. R. 
Grove (Lord Justice Sir William Grove) remarked that a practical application 
of the science appeared to be still distant. The great desideratum, in his opinion, 
was not so much improvement in the machine as in the prime mover, the battery, 
which was the source of power. At present the only available use for this 
power must be confined to special purposes where the danger of steam and the 
creation of vapour were sought to be avoided, or where economy of space was a 
great consideration. Professor Tyndall agreed with the last speaker, but sug- 
gested that there might be some way of mitigating the apparent diminution of 
power due to the induction of opposing electromotive forces in the machine 
itself. Mr. C. Cowper spoke of some experiments, made by himself and Mr. E. A. 
Cowper, showing the advantage gained by properly laminating the iron cores 
used in the motor. He put the cost of electric power at 4/. per horse-power per 
