ELECTRO-MOTIVE ENGINES 227 



certain mechanical resistances, and thus a portion of the force is lost. This takes place 

 in every cell of the voltaic arrangement, and consequently the proportion of zinc which 

 is consumed, to produce any final mechanical result, is considerably greater than it 

 should be theoretically. 



Joule gives as the results of his experiments, the mechanical force of the current 

 produced in a Darnell's battery as equal to 1,106,16011)8. raised one foot high, per 

 pound of zinc, and that produced in a Grove's battery as equal to 1,843,600 Ibs. raised 

 one foot high, per pound of zinc. 



It need scarcely be stated, that this is infinitely above what can be practically ob- 

 tained. A great number of experiments, made by the Author some years since, enabled 

 him to determine, as the mean average result of the currents, produced by several forms 

 of battery-power, that one grain of zinc, consumed in the battery, would exert a force 

 equal to lifting 86 Ibs. one foot high. Mr. Joule and Dr. Scoresby thus sum up a series 

 of experimental results : Upon the whole, we feel ourselves justified in fixing the 

 maximum available duty of an electro-magnetic engine, worked by a Daniell's battery, 

 at 80 Ibs. raised a foot high, for each grain of zinc consumed.' This is about one-half 

 the theoretical maximum duty. In the Cornish engines, doing the best duty, one grain 

 of coal raised 143 Ibs. one foot high. The difference in the cost of zinc and coal need 

 scarcely be remarked on. The present price of the metal in sheets is 281. per ton, and 

 coal can be obtained, including carriage to the engines, at less than 11. per ton ; and 

 the carbon element does two-thirds more work than can possibly be obtained from the 

 metallic one. 



By improving the battery arrangements, operators may eventually succeed in getting 

 a greater available electrical force. But it must not be forgotten, that the develop- 

 ment of any physical force observes a constant law. Whether in burning coal in 

 the furnace, or zinc or iron in the battery, the chemical equivalent represents the 

 theoretical mechanical power. Therefore, the atomic weight of the carbon -atom being 

 6, and that of the zinc-atom being 32, it is not practicable, under the best possible 

 arrangements, to obtain anything like the same mechanical power from zinc which 

 can be obtained from coal. Zinc burns at an elevated temperature ; in burning a 

 pound of zinc there should be obtained, as heat, the same amount of mechanical power 

 which is obtained as electricity in the battery. The heat being more easily applied 

 as a prime mover, it would be far more economical to burn zinc under a boiler, and to 

 use it for generating steam-power, than to consume zinc in a voltaic battery for 

 generating electro-magnetical power. 



With the advance of our knowledge some of the difficulties may be overcome. An 

 important and substantial step in advance has been made in practical electricity by 

 M. Gramme, of Paris, who substitutes a rotatory for a reciprocating motion in the me- 

 chanical arrangement employed in the production of an electrical current. Hitherto 

 magneto-electric machines have acted upon a principle analogous to that of the ordinary 

 pump, and the current produced has consequently been intermittent in its character. 

 The new machine acts in a similar manner to the rotary pump, and, like that apparatus, 

 gives a continuous stream, and with a very small expenditure of power, while the great 

 drawback to other systems, self-heating, is in it scarcely appreciable, It is, moreover, 

 the first recorded instance of a perfectly continuous magneto-electric current having 

 been obtained on a practical scale, and the circumstance derives additional interest 

 from the fact that the inventor is from the ranks of mechanical workers in electrical 

 science, and not a highly-educated electrician. Had he been one, the probability is 

 that the present apparatus would never have been invented by him, for to obtain a 

 continuous stream an electrician would have followed a course of experiment and in- 

 ductive reasoning which would have landed him in an entirely opposite direction. 

 Even M. Gramme's explanation of the reasons operating to produce the results he has 

 achieved are at variance with several known facts in electrical science, and with the 

 views entertained by electricians upon the subject. The production of the apparatus 

 is therefore to be attributed more to intuition on the part of its inventor than to the 

 study and practical application of the laws which govern the artificial production of 

 electrical currents. The machine by means of which this important improvement is 

 effected is composed of three rings of soft iron encircled with an endless coil of copper- 

 wire. Each of these rings is made to rotate between the two poles of a strong electro- 

 magnet. The magnets are vertical cylinders of soft iron 3ft. 6 in. high by 3g-in. in 

 diameter, and are coiled round with insulated copper-wire. They are connected at the 

 top by a square cast-iron plate, and at the bottom are let into a base-plate 2 ft. 8 in. 

 square. In operation the half of each ring which is in proximity with the north end 

 of the magnet takes south polarity, while the opposite half near to the south end takes 

 north polarity. The two neutral points of the system are equi-distant on each side. 

 The rings or bobbins are rotated on a horizontal axis, and when they are set in motion 

 their polarity remains unchanged in position with regard to the operator. The action 



