VOLTAIC ELECTRICITY. 



97 



VOLTAIC ELECTRICITY. 



APPLICATIONS OF THE ELECTROMAGNET THE ELECTRIC BILL 

 KLKCTKO-MUTOU8 MAONETO-ELBCTBIC MACHINES O THE 

 OLD TYP. 



IN* oar last lesson wo loarnt how a piece of iron can be converted 

 into a powerful magnet, by making it the core of a coil of wire 

 through which an electric current oan bo made to flow. The 

 applications of the eloctro-magnot are endless ; indeed, we may 

 broadly state that there are no contrivances, be they big or 

 little, which depend for their efficiency upon the power of elec- 

 tricity, which do not in some form or other employ electro- 

 magnots. In the electric organ, for instance, magnets arc om- 



immediately flies back to iU original position, to b 

 attracted as soon as it once more touches the connecting spring. 

 In this way it is kept moving to and fro, striking the bell at 

 every advance towards the magnet. In the illustration, a hone- 

 shoe form of magnet is shown, but it is now usual to make one 

 like Fig. 77, which is in reality much the same thing, bat is far 

 more convenient in practice. It takes up less room, and the 

 bobbins oan be wound separately and with great speed on a 

 lathe. But beyond those minor uses for the electro magnet, we 

 find others of far greater importance, which are, perhaps, des- 

 tined at no distant date to cause a great revolution in many arts 

 and manufactures. 



It is natural to man to be fond of the marvellous. The Philo- 



Pig. 78. 



ployed to open the valves to admit wind to the pipes, instead of 

 the usual mechanism ; and although such organs are rarely built, 

 they are useful in situations where the key-board is placed at 

 some distance from the body of the instrument. In Clowcs's 

 type-composing machine, electro-magnets control the ejection 

 of the metallic letters from their receptacles. But to come to 

 more ordinary uses of the electro -magnet, wo find in the electric 

 bell, now so common in large buildings and modern houses of 

 the better class, a good illustration of its successful employment. 

 In Fig. 76 is shown a form of electric bell which, perhaps, 

 better exhibits its mode of working than if wo gave one of more 

 modern and compact construction : T is the gong, and K the 

 hammer, which is urged against it by being attracted by the 

 electro-magnet e. This bell is of the common form known as 

 a trembler, for instead of giving a single stroke, the hammer is 

 caused to vibrate to and fro, so that an incessant ringing is 

 produced so long as the current is in action. This is managed 

 in the following way : The current is carried to the hammer, 

 the lower part of which forms an armature to the magnet, by 

 the spring g. But directly it moves to the magnet, it is drawn 

 away from the spring, and therefore the circuit is broken. It 



137 X.K. 



sopher's Stone which was to change the baser metals into gold, 

 the search for which was the ruin of so many ardent workers, 

 finds its counterpart in many branches of science. The dis- 

 covery of that ignis fatuus called " perpetual motion " was 

 the dream of numbers of mechanics before science taught tho 

 grand doctrine that energy, whether it take the form of motion, 

 heat, chemical action, or what not, can neither be created nor 

 destroyed. We can easily imagine that when the first experi- 

 ments were made with the electro- magnet when it was shown 

 that immense weights could, under certain conditions, be sup- 

 ported by a comparatively small piece of iron when it was found 

 that the magnetism ceased directly the circuit was broken, and 

 could be instantly renewed when contact with the batte: 

 once more made good there were numerous dreamers who saw 

 before them the means of gaining something very much akin to 

 perpetual motion. Hence, in looking back to the past history 

 of mechanical contrivances, we find an important place assign? i 

 to those machines which their inventors hoped would one day 

 supplant the steam engine. 



The simplest in construction cf these electro- motors is that 

 of Froment, in which a revolving drum, armed with bars of 



