EXHIBITION OF ELECTRICITY AT PARIS. 



253 



devoted to his exhibits, and the remainder 

 lighting the grand stairway, were operated by 

 his enormous steam dynamo of one hundred 

 and twenty-five horse-power. The Maxim in- 

 candescent light was also very fully shown, 

 about two hundred lamps being in operation. 

 The Swan and the Lane-Fox lamp, and the two 

 English incandescent lamps, made good dis- 

 plays, but neither are as complete as the sys- 

 tems of Edison and Maxim. 



Outside of electric lighting the exhibition 

 was full and varied, but space can only be 

 given here to a few of the more notable de- 

 vices, including one or two others which were 

 not illustrated at the exhibition. 



Sir William Thomson has made a careful 

 mathematical calculation of the conditions of 

 transmitting water-power from Niagara to Phil- 

 adelphia, Boston, New York, Montreal, and all 

 places within a radius of three hundred miles. 

 The dynamo-machines of Gramme or 

 Siemens, supplemented by the Faure 

 storage battery, make it demonstrably 

 practicable to transmit the power of 

 water-falls for long distances and use it 

 for mechanical work with less dissipa- 

 tion of energy than in ordinary hydrau- 

 lic and mechanical contrivances for trans- 

 mitting power a few hundred yards. He 

 proposes to convey the current by a solid 

 copper wire carried over-head like ordi- 

 nary telegraph wires. A current of 240 

 webers can be transmitted 300 miles by 

 a wire J inch in diameter, receiving en- 

 ergy at the rate of 26,250 horse-power 

 from dynamos driven by the Niagara 

 water-fall, and discharging it at the far- 

 ther end at the rate of 21,000 horse- 

 power. The loss of 20 per cent by conver- 

 sion into heat in the conductor would not 

 raise the temperature of the wire above that 

 of the surrounding atmosphere more than 

 20 centigrade. The potential of 80,000 volts 

 on the conductor would not render the isola- 

 tion of the wire difficult, nor would it be dan- 

 gerous to manage in the central station ; but 

 when applied to miscellaneous practical uses 

 it must be reduced to 200 or 100 volts. This 

 can be done by the medium of the Faure bat- 

 tery. A battery of 40,000 cells can be con- 

 nected directly with the electric main ; and at 

 short and regular intervals a small number ot 

 the charged cells can be removed and replaced 

 by new ones. Sets of fifty could thus be con- 

 stantly replaced, and the charged cells placed in 

 connection with the supply circuit. In elec- 

 tric transmission of power high potential is a 

 condition of economy. The idea of the appli- 

 cation of water-power at a distance by electric 

 transmission was first suggested by C. W. Sie- 

 mens in 1877, and has been made the subject 

 of thorough theoretical study by Sir William 

 Thomson, who stated the results of his calcu- 

 lation in an examination before a parliament- 

 ary committee on electric lighting in May, 1879, 

 and called the attention of the British Associa- 



tion to the subject in an address at the meet- 

 ing of 1881. 



The Gramme machine was the first electro- 

 motive device which proved practically valua- 

 ble. It consisted of a ring of iron, with a coil 

 of insulated wire wound around its rim, ro- 

 tated between the poles of an electro-magnet. 

 The leading feature was the commutator, which 

 kept the current always running in the same 

 direction and perfectly continuous, and allowed 

 of the current being used to increase the power 

 of the electro-magnet, besides doing the me- 

 chanical work required of the machine. The 



GRAMME 8 DYNAMO-ELECTKIC MACHINE. 



same method of economizing the electricity 

 was worked out by Siemens and Wheatstone ; 

 but its development by Gramme first led to 

 the practical use of electricity for the genera- 

 tion of light. Various new modifications of 

 the dynamo-electric machine were shown at 

 the Paris International Electric Exposition of 

 1881. Surprise was caused among the electri- 

 cians by the exhibition of electrical machines 

 invented in 1860, and described in 1864 by Pro- 

 fessor Pacinotti, of Cagliari, which contain all 

 the essential features of Gramme's later in- 

 vention and some of the improvements which 

 have been added. 



A newly invented machine by Dr. Hopkin- 

 son consists of twenty-four fixed magnets ar- 

 ranged in two opposite circles with unlike poles 

 facing each other, between which revolves an 

 iron ring in which channels are cut out alter- 

 nately on the opposite sides. It thus presents 

 square projections, around which as cores are 

 wound bobbins of wire, whose ends are at- 

 tached to the arms of the commutator. This 

 device allows the current to be taken from any 

 opposite pairs of arms in the commutator by a 

 number of brushes. 



The Burgin machine has field-magnets like 

 a Siemens machine, and an inside ring, which 



