Show ari ws i afi lne in machinery chinery la for electricity tri city THE FIRST DYNAMO comparison between it and the present powerful electro magnets the first dynamo electric machine ever constructed was made by faraday this great physicist the prince of experimenters peri menters as he has been called discovered that when a disc or flat plate of copper was made to rotate between the poles of a magnet currents were produced in the plate from the center outward by making a wire touch the revolving plate with one of its ends and bringing the other one in contact with the rim he found that a current of electricity passed along the wire and could be made to indicate its existence by deflecting ting the needle of a galvanometer decomposing a chemical solution or by any of the well known effects produced by electricity in motion faraday saw the importance of this discovery and the great uses in the way of practical application to which it might be pat but he did not himself stay to develop it he left that to others and with it the wealth which might thus be acquired and himself went on to investigate other obscure and little known phenomena connected with physics and electricity regarding this as his proper work and exhibiting in his conduct the true scientific spirit when many years afterward he went to see the first application of this discovery of his to the production of the illumination of the north foreland lighthouse he said after looking at the large mag neto electric machines there 1 I gave it to you an infant you have made it a giant dynamo and magneto electric machines consist essentially of a coil of wire the armature as it is called rotating between the poles of a large magnet the poles being bent round so as to approach each other and have the armature between them this magnet may be either a permanent magnet of hard steel or an electromagnet electro magnet consisting of wire coiled round a soft iron core a current of electricity being made to circle round the wire coil and thus magnetize ing the iron core while it lasts it is aba latter arrangement which is almost universally ver sally used now though the magneto machines with permanent magnets were tho earliest form THE MAGNET A magnet produces an influence in the neighborhood around it and this surrounding neighborhood is known as the field of force of the magnet i e the sphere in which its influence can be felt A magnetic needle or bit of iron filing placed in this field sets itself to point along the lines of force of the field that is the lines along which the magnetic force acts and which form curves round the magnet running out as it were from pole to pole and curving round to tho other any one may see the form of these lines of force for himself by placing a bar magnet underneath a sheet of paper and then sprinkling filings on the paper on tapping this the filings will set themselves along the lines of force in beautiful regular curves here the small fragments of iron are themselves made magnet while under the influence of the powerful magnet in whose field they are and therefore place themselves lengthwise along the lines of force that is along th line of action of the result ant magnetic force at the place where each one is when a coil of wire or armature is made to revolve rapidly in the strong field of force which occupies the space between the poles of a powerful electromagnet currents are produced in the coil these currents alter their direction through the coil every time the latter changes its position with reference to the poles of the magnet the side of the coil which was opposite the north pole is after half a revolution opposite the south pole and the influence of the south pole tends to produce an opposite current to that of the north pole here we have an alternate current dynamo machine PROCESSES OF THE As the coil or armature rotates with great speed some hundreds of revolutions per minute these currents in alternating terna ting directions succeed each other very rapidly and if an electric arc lamp is placed on the circuit it will be lit up in this case it is not necessary that the current be sent round the circuit in one direction only but although the terminals of the lamp are constantly changing their polarity that is the north pole where the current enters the next instant becomes the south pole where the current leaves yet as this occurs many times in one second the effect produced ia the same as if the current waa in one uniform direction the lamp has no time to cool it does not go but before the oppositely directed passes through it and produces the same effect as the previous one no flickering is observable the impression produced by the glowing carbon on the human eye is retained by the retina for a far longer period than the duration of one surge of electricity through the lamp and is not gone before the effect produced by the succeeding opposite wave makes its impression on our nerves in a continuous current dynamo which is necessary for gome purposes such as electroplating electro plating where the effect desired could not be produced if the direction of the current was continually altering atie electric current is made to pass always one way round the external circuit this result is got by using the ingenious device of a which automatically deflects the current BO as always to send it in an unvarying direction through the plating bath or the electric lamp as the case may be knowledge |