ELECTRIC LIGHT 207 



an insulated conductor 3,300 feet long, consisting of a bundle of seven No. 10 copper- 

 wires, laid parallel to each other and bound with a double covering of linen tape ; the 

 extremities of this conductor are connected with the studs k k, thereby connecting 

 them with the wires h h. The currents of electricity which produce the light are 

 taken from steel collars by means of springs g g, thence to the studs at I /, from which 

 they can be conveyed by conductors to any required place. The power necessary to work 

 such a machine as this is derived from a seven -horse engine, at a cost for coal of one 

 halfpenny per hour. In addition to this must be added the expense of the carbon 

 rods for the lamps, which will be about ten inches per hour, worth perhaps a penny. 

 The total cost of working, including interest on the cost of purchase of machines, 

 expense of maintenance and repairs, would be perhaps about 4d. or Sd. per hour. 

 The light produced is estimated to have an intensity equal to 6,000 wax candles. A 

 more detailed account of this machine will be found in the ' Quarterly Journal of 

 Science,' No. XII. October 1866. 



Mr. Wilde has lately introduced some improved apparatus for the production of 

 light of great intensity. His machine, as recently employed, consists of two parts an 

 electro-magnetic induction machine for producing the electricity, and an arrangement 

 for regulating the light produced by the current, and projecting it upon distant objects. 

 The electro-magnetic induction machine is founded upon a new and somewhat para- 

 doxical principle discovered by Mr. "Wilde that magnets and electric currents inde- 

 finitely weak can produce magnets and currents of indefinite strength. The machine 

 consists of a circular or cylindrical framing of cast iron, round the interior of which are 

 arranged a number of electro-magnets at equal angular distances from each other. A 

 cast-iron disc is mounted on a driving shaft, running bearings fitted to each side of 

 the framing, and carries a number of armatures revolving before the electro-magnets. 

 A slight charge of magnetism is imparted to the electro-magnets before the machine is 

 used for the first time by transmitting a momentary current through the wires sur- 

 rounding the iron cores, or by touching their extremities with the poles of a permanent 

 magnet. This initial charge is always retained by the electro-magnets, and is the 

 basis of the augmentations of the electricity and magnetism produced by the rotations 

 of the armatures. As the armatures revolve they become slightly magnetised in their 

 passage between the poles of the electro-magnets, generating weak currents in the 

 insulated wires surrounding them. These currents are transmitted by means of a 

 commutator through the wires surrounding the electro-magnets, so as to increase their 

 magnetism, until, by a series of actions and reactions of the armatures and electro- 

 magnets on each other, the magnetism is exalted to the highest degree of intensity 

 and the most powerful currents of electricity are produced. A small fraction of the 

 current thus produced is sufficient to sustain the power of the electro-magnets, while 

 the major portion of the current produces the light. The machine is 28 in. high, 

 34 in. in length, and 21 in. in diameter. Its weight is 11 cwt. About four-horse 

 power is required to drive it a velocity of 600 revolutions per minute, and this driving 

 power is obtained from the fly-wheel of a small steam-engine. At this velocity the 

 current will fuse an iron wire 6 ft. long and O'Oo in. in diameter, and will burn ' car- 

 bons ' half an inch square. In this machine the alternating current is used for pro- 

 ducing the light, past experience in lighthouse illumination having proved it to be 

 greatly superior to the direct or continuous current, since it has the important advan- 

 tage of consuming the carbons equally, and thus always retains the luminous point in 

 the focus of the optical apparatus used in connection with the machine. The alter- 

 nating current also dispenses with commutators, and the destructive spark on the 

 rubbing surfaces is also avoided when the light may be accidentally extinguished, or 

 when the circuit becomes broken from any other cause. The carbons as they consume 

 are made to approach each other by means of a right- and a left-handed screw, the 

 screws being made to act independently of each other, so as to allow of the adjustment 

 of the carbons to the focus of the optical apparatus used for projecting the light. The 

 regulator with its carbon points is placed in the focus of a catadioptric lens, which 

 parallelises the divergent rays of the light into a single beam of great intensity. 



This machine has been introduced to the Admiralty by Mr. Wilde, and the following 

 account of some experiments made at Portsmouth, on board the ' Comet,' with a view 

 to test the power of this electric light as a means of detecting the advance of torpedos, 

 or anything indeed, at night, over the sea, is quoted from the 'Times' of Feb- 

 ruary 23, 1874: 



' The Naval Torpedo Committee have given the subject of attack by torpedo boats 

 at night upon ships at anchor considerable attention, and have proved by experimental 

 practice that in the majority of instances the torpedo attack upon the ship must be 

 successful. The "Monarch," one of the ships experimented upon, was anchored at 

 Spithead, and on one occasion was considered to have been made almo; t impregnable 

 against any attack by a strong crinoline framework of booms and spars built up round 

 her, supplemented by her boats rowing guard round her within hailing distance. 

 The ship had also the advantnge of knowing that a boat torpedo attack would 



