SCIENCE, EDUCATION, RELIGION 



711 



called, excites it, causing it to exert an attrac- cessful attempts to make both, the experimenters 

 tion or pull upon another part of the machine i did not appear to even guess that there was any 

 known as the armature. The armature is also particular connection between them. The de- 

 wound with wire through which the current signing of motors does not stop with the simple 

 s, and is placed between the extremities : application of the revolving wheel principles 

 of t he field magnet which are called poles. The j explained above, but furnishes unlimited room 

 electrical connections are so adjusted that the j for skill in making them in forms convenient 

 at traction or pull between the field and armature for use, and adapted for direct connection to 



up on one side of the armature and down on 

 the other, thus causing the latter to rotate with 

 any desired speed and power according to the 

 sire of the motor. The power may be Drought 

 in by wires through the window-casing, and the 

 whole machinery started and stopped by turning 

 a switch. Being entirely noiseless, perfectly 

 clean. Mi-ceptible of being started, regulated, 

 :>ped as stated by the mere pressure of a 

 button, and cheap, both in constructing and 

 ting, its utility for the lighter kinds of in- 

 dustrial service is beyond question. There is no 

 delay with electric motors similar to that in 

 getting up steam in a steam-engine, and this 

 quality is of the utmost importance in the fire- 

 engine service, and is made use of in the electric 

 fire-engine. Upon reaching a fire the connecting 

 wire< from the electric engine are hooked into 

 the box on the electric light post, from which 

 \\ircs run up to the electric light wires above. 

 The engine is then ready for instant operation 

 at full power. The revival of interest in the 

 electric motor causes it to seem like a new in- 

 vention to those not familiar with the record 

 of electrical science. As a matter of fact, the 

 elect rieian Jacobi, under the patronage of the 

 i Russia, propelled a boat on the Neva 

 by electricity more than half a century ago; 

 and not many years later Professor Page, in this 

 country, succeeded in driving a car by an electric 

 locomotive between Washington and Bladens- 

 Imrg at a speed of nineteen miles an hour. But 

 nothing resulted from those early experiments 

 on account of the rudimentary methods of 



various kinds of machinery. American inge- 

 nuity has undoubtedly taken the lead in making 

 motors of all kinds. 



The Trolley. An electric street car, such 

 as may be seen in the majority of towns and 

 cities throughout the Union, is known as a 

 trolley car because the current is taken from 

 the overhead wire through the trolley or wheel, 

 whence it goes down the pole and through a 

 wire to the motor which is situated under the 

 floor, then into car wheels and so to the rails 

 and ground and back to the generator or dynamo 

 in the power station. 



Electric Light, is one of the many electric 

 processes which depend upon the faculty of being 

 easily converted into heat at any desired place 

 and in any part of its conductor. In itself elec- 

 tric lighting covers a range of sizes or powers 

 more extensive than the candle, the gas-burner, 

 and the calcium light combined. Heat is the 

 vibratory motion of the atoms which compose 

 substances, which kind of motion electricity 

 always produces when moving through a con- 

 ductor. The temperature increases with the 

 current, and it becomes possible, therefore, to 

 raise the temperature of a given conductor to a 

 red or white heat. If such a current be sent 

 through an iron, a copper, or a platinum wire it 

 will glow very brightly and be in danger of fusing; 

 but if a filament of carbon be used instead, in- 

 closed in a vacuum, it cannot fuse, but gives out 

 a bright light. It is also a great advantage to 

 be able to produce intense heat at a particular 

 spot by passing a current through a wire and 



generating electricity; and had not the dynamo \ thinning the wire at the desired place. Tfie 

 machine been made commercially successful ; higher incandescent or luminous heat is obtained 



tor would still be floating in the brain of 



scientists as a future but very indefinite possi- 



bility. Now, however, it has been caught and 



objective. Thousands of electric motors 



are at work in various parts of the country, 



ra ntring in capacity from one-half to twenty 



horse-power, and they are transferring freight 



and passengers, running printing-presses, lifting 



elevators, clriving ventilators, and making them- 



jeiierally useful at domestic and industrial 



laptahilitv of the motor for 



reet railways is its chief recommen- 



to the American people. 



The Dynamo. This machine is very like 

 odern motor just described. In fact a 

 dynamo may be used as a motor by supplying 

 it with electricity from another dynamo or any 

 oiher source of electricity, ami if the armature 

 of a motor be rot me or other 



prime mover, it will give a current of electricity 

 and be* namo. The 



laiim and motor 

 in the proportioning of par' odes of 



regulating speed 



' 'nly after 



vention of the modern dynamo was this fact 

 discovered, and in the early and partially sue- 



by making the section of the wire still thinner. 

 which brings it to a heat of dazzling brilliancy. 

 This is the whole principle of the incan 

 electric light in a nutshell. Klectric lights are of 

 two classes, known as "arc" and "incandes- 

 cent. 11 The latter, named from the ii. 

 heat of the thin \\ire. consists of a fine wire or 

 filament of any substance \\hich will Mnnd 

 enormous heat, inclosed in a glass, with the air 

 removed to prevent its burning up at the high 

 temiK-rature. These lights, which are usually 

 small, are very soft and pleasant to the -. 

 are used for indoor illumination. The arc light 

 is produced by the current passing from t 

 of one rod of carbon to the end of another rd 

 through the vapor produced by the burning of the 

 carl-oil and i> named from the curved Of arc- 

 shaped path which the current takes in pasting 

 through this vapor. The passage of the 

 heats the particles of carbon in the vapor 

 as well as the tips of the rods to an intense 

 degree, and gives off a light of absolutely unap- 

 proached brilli.n u^-d for street 



illuminatioi 



have been tried in the more important light- 

 houses of the world. An ordinary gas burner 



