June 8, 1876] 



NATURE 



135 



Great difficulty is experienced in properly adjusting the 

 resistances and dividing the current, for the production of 

 such a number of lights as is required in the cases of the 

 first kind, and extensive experiments to overcome this 

 difficulty have as yet been attended with only partial 

 success. 



It is to those of the second kind that we purpose to 

 draw attention. Here the circumstances are quite altered, 

 the cases of application are numerous, and the apparatus 

 employed is perfect and proportionally cheap, and yet it 

 is adopted not nearly so frequently as might be expected. 

 A constant light equal to that of from 9,000 to 10,000 

 stearine candles can easily be produced, with a motive 

 force of from eight to nine horse-power, and this at a 

 cheaper rate than any other artificial light. 



Such apparatus have lately been employed in various 

 countries for various purposes, such as for engineering 

 works, torpedo defences, signal lights, and in military field 

 operations. It is to be hoped that its adoption in this 

 country will soon be more general. 



The following is a description of Messrs. Siemens Elec- 

 tric Light Apparatus, one of many that have been adopted 

 in various countries. Comparative experiments have 

 proved it to be the most powerful and at the same time 

 the least expensive of all apparatus yet employed in the 

 production of continuous electric light. It is a com- 

 plete apparatus by itself, in which the core of the 

 armature is fixed and the wire-helix alone caused to 

 rotate. By fixation of the armature core great inductive 

 power is obtained, and consequently powerful currents. 



Fig. 2. — End Elevation and Longitudinal Section of Dynamo-electric Light Machine. 



With about 380 revolutions of the wire-helix per minute, 

 and nine to ten horse-power, a light equal to 14,000 candles 

 is obtained. 



The principle in this and all other magneto-electric 

 machines is, that when part of a closed electrical circuit 

 is passed between the poles of a stationary magnet, a cur- 

 rent is generated in the circuit the direction of which 

 depends upon the position of the magnetic poles and 

 direction of motion of the conductor. 



In this machine (shown in Figs, i and 2) the conductor, 

 by the motion of which the electrical current is produced, 

 is of insulated copper wire, coiled in several lengths, and 

 with many convolutions on a cylinder of thin German 

 silver, and in such a manner that each single convolution 

 describes the longitudinal section of the cylinder. The 

 whole surface of the metal cylinder is thus covered with 



wire, forming a second cylinder closed on all sides {a, b, c, 

 d, Fig. 2). 



This hollow cylinder of wire incloses the stationary 

 core of soft iron (« s s' «' Fig. 2) which is fixed by means 

 of an iron bar in the direction of its axis, prolonged at 

 both ends through the bearings of the wire cylinder to 

 standards. Surrounding the wire cylinder for about two- 

 thirds of its surface, are the curved iron bars (n n' s s' 

 Fig. 2), separated from the stationary iron core by space 

 only sufficient to permit the free rotation of the wire 

 cylinders. The curved bars are themselves prolongations 

 of the cores of the electro-magnets (e E E e) and the sides 

 of the two horse-shoe magnets (N<?— S, m and nV — S', m) 

 are connected by the iron of the two standards (om and 

 o'm'). 



As the coils of the electro-magnets form a circuit whh 



