The Montgomery advertiser., 1901-08-30
ELECTRICAL ENGINEERING
By Arthur E. Watson, A. N.
 ARTICLE VII.
MOTORS FOR DIRECT CURRENTS

MOTORS FOR DIRECT CURRENTS.
 To make something that will go is a laudable ambition for anyone. The in- vention of the electro-magnet at once revealed to the early inventors the pos sibility of producing mechanical rota- tion. That a piece of iron could be made strongly magnetic and exert a powerful pull toward another piece ot iron. then in an instant lose that att traction only to acquire it again. at the proper moment, was to them process analogous to the admission and cut-on of steam in an engine cylinder. In decade host of electro magnetic en- giEes had been made and either de- molished or kept as curiosities. Many so- called battery motors" in more re- cent times illustrate the same con- struction and defects.
 The uselessness of these early motors can be partly attributed to the lack of sufficient current-batteries being the only source-but principally to internal causes that were made evident when large currents were available. Nearly every one of these pioneer toys was constructed on the make and break principle-that Is. contact on the re- volving shaft would touch ,a springy brush. thereby making" the electric circuit: an electro magnet would be energized and attract a neighboring | "rotatable'' piece of iron. When this piece was closest to the poles the brush would slide off the contact and break ing" the circuit, deprive the magnet of it's strength: momentum would continue the rotation until another magnet or piece of iron was suitably located to give another pull, and so on by series of rapid makes and breaks until the rotating member acquired lively speed. It is easy for the modern scien- lists to see the error of former con struction. In general these were four First the rotative force or "torque' was spasmodic. Second. the distances through which the magnetic force had to operate were relatively large and at the very moment when the magnetic field" was strongest the current was shut off Third. a current could not be instantaneously established or broken; an influence akin to inertia is associat- ed with a current and its magnetic field; at make" the current does not have time to reach it's full value and at break" the current is unduly prolong- ed combining its sluggishness with the | unavoidable residuar magnetism to ex- ert a backward pull on the revolving mass and causing vicious sparkling at the brushes. Fourth. the rapid surging of the lines of force through solid | masses of iron generated wasteful eddy currents. Another name for such mo- tors is the "oblique approach" the re- volving bars getting closer and closer | by a sort of oblique path.
 | Though illustrating great ingenuity, l such motors probably do not have 10 per cent. sufficiency, especially should such construction be tabooed in bat tery'' motors. In the trade now bat >tery motor means such cheap con- trivance that 1t would be ruinei 1T l attached to a decent circuit. When batteries represent the most expressive means of generating electricity certain lY it behooves the purchaser to secure the most efficient motor. Based on per- l formance of these early devices text known college text book. published be- fore 1870. states Though an interest ing application of the transformation of energy there is no expectation that these ma chimes will ever be practically applied in manufactureS.'
 Some of these early experimenters seem to have known that a machine | which would generate current of elec- | tricity would also run as motor if current was sent through 1t, but they | certainly failed to appreciate the sig nificance of the fact. It remained for Gramme in 1873 to use two identical | machines one as a generator supplying current to the other. running thereby as a motor. The exhibition was made | in Vienna. and represented the be- l ginning of electric power transmission. | One prominent scientist has declared this to be the greatest discovery of modern times. When the present far reaching effects of elctric motors are considered ore would hesitate to con- | tradict the assertion.
 | Just why the currents under the two
 poles are in opposite directions will also be seen from reference to the same figure. If current arrives by the upper
 brush. one-half will pass around the ring on the right going in the outer wire from the observer and toward him in the other half. Outer wires only are affected by the field of force, for the lines pass from one pole to the other. not diametrically through the armature, but through the curved body of the ring.
 Fleming has devised an easy rule for
 predetermining the direction of rota-
 ton of a motor If the direction of the lines of force Ohe polarity) and the di-
 rection of the current are known
 These three motions are at right angles to each other. and like the corners or a box. With the left hand let the fore finger. the thumb and the second tln- ger be held at right angles to each other. If the forefnger points in the direction of the lines of force (from N. to S.) the second finger in the direction of the current-preferably selecting a
 wire under the center of a pole-the thumb will point in the direction of the resulting motion. A similar rule using the right hand. will apply to gene rator. If the forefinger points in the direction of the lines of force - radi-
 ally into the armature-the thumb in the direction of rotation, the second finger will show the direction of the
 induced electro motive force. Quitting for a moment the cause of rotation and applying this right hand rule. select a wire under the middle of the north pole. and the first finger will point hoIi" zontally. parallel with the plane of paper. the thumb will point vertically in the plane of the paper. and the sec ond finger will point directly towards
 the observer. Then in case of a motor.
 the electro motive force developed hg the rotation of the armature Is directly opposed to the current which produces the motion. To this has been technical ly given the name counter electro mo