Part 4

In an electric motor the horseshoe magnet is called the field magnet, and the rotating part is called the armature, while the device by means of which the direction of the current through the armature coil is reversed is called the commutator. In this last figure it will be noticed that the coils wound upon the field magnet are represented as of wire much finer than that wound upon the armature. In actual practice machines are sometimes wound in this way, and sometimes the field wire is twice as large as that on the armature. When the field wire is very much finer than that of the armature the machine is what is known as shunt wound, which means that only a small portion of the current that passed through the armature passes through the field coils. Although with this type of winding the current that passes through the field coils is very weak, the magnetism developed thereby can be made greater than that of the armature if desired. This result is accomplished by increasing the number of turns of wire in the field coils. Thus if the current through the armature is one hundred times as strong as that through the field coils, the latter can be made to equal the effect of the former by increasing the number of turns in the proportion of one hundred to one, and if the increase is still greater the field coils will develop the strongest magnetism. The reason why a small current passing around a magnet a great many times will develop as strong a magnetization as a large current, can be readily understood when we say that the magnetism is in proportion to the total strength of the electric current that circulates around the magnet. Suppose we have two currents, one of which is one thousand times as strong as the other, then if the weak one is passed through a coil consisting of one thousand turns it will develop just as strong a magnetization as the large current passing through a coil of only one turn. This last explanation enables us to see how it is that the comparatively small current that can pass through the contact between the trolley wire and the trolley wheel can develop in the motor force sufficient to propel a heavy car up a steep grade. When that small current reaches the car motors it passes through a thousand or more turns of wire, and thus its effect is increased a corresponding number of times.

A motor having a single coil of wire upon the armature, as in Fig. 10, would not give very satisfactory results, owing to the fact that the rotative force developed by it would not be uniform. Such motors are made in very small sizes, but never when a machine of any capacity is required. For large machines it is necessary to wind the armature with a number of coils, so that the rotating force may be uniform, and also so that the current may be reversed by the commutator without producing sparks so large as to destroy the device. When an armature is wound with a number of coils the direction of the current is reversed, by the commutator, in each coil as it reaches the point where its usefulness ends, and where, if it continued to flow in the same direction, it would act to hold the armature back. The effect of this reversal of the current in one coil after another is to maintain the polarity of the armature practically at the same point, so that the strongest pull is exerted between it and the field magnet poles at all times. To explain clearly the way in which the commutator reverses the current in one coil at a time it will be necessary to make use of a diagram illustrating what is called a ring armature. Such a diagram is shown in Fig. 11. The ring _A_ is the armature core, and is made of iron; the wire coils are represented as consisting of one turn to each coil, and are marked _w w w_. The current enters the wire through the spring _B_, and passes out through _C_. As can be seen, the current from _B_ can flow through the coils _w w_ in both directions, thus dividing into two currents, each one of which will traverse one half of the wire wound upon the armature. The two half currents will meet at _C_. If the armature is rotated the springs _B_ and _C_ (which are called commutator brushes) will pass from one turn of the wire coil to another just back of it as the rotation progresses, and each time that contact is made with a new turn the direction of the current in the turn just ahead will be reversed. The current in the wire as a whole, however, will always be in the same direction--that is, in all the turns to the right of the two brushes; the current will flow toward the center of the shaft on the front side of the armature, and away from the shaft in all the turns on the left side. As the direction of the current on opposite sides of the brushes is always the same, the poles of the armature will remain under _B_ and _C_, therefore the relation between the position of the poles of the armature and the field magnet will be the same substantially as that illustrated in Fig. 10, and, as a result, the force tending to produce rotation will at all times be the greatest possible for the strength of the current used and the size of the magnets.

Armatures are wound with a number of turns of wire in each coil, unless the machine is very large, and present an appearance more like Fig. 12. In this figure the brushes are arranged to make contact with the outer surface of the ring _C_, which is the commutator. The segments _s s_ are connected with the ends of the armature coils _c c c_, but are separated from each other by some kind of material that will not conduct electricity--that is, they are electrically insulated. As will be noticed from this, the armature in Fig. 11 acts as a commutator as well as an armature, its outer surface performing the former office. In the winding the difference between Figs. 11 and 12 is simply in the number of turns in each coil, there being one turn in Fig. 11 and several in Fig. 12.

The armature shown in Fig. 10 is of the type called drum armature, but it can be wound so as to produce the same result as the ring, although it is not so easy to explain this style of winding. It will be sufficient for the present explanation to say that whatever type of armature may be used, the winding is always such that the direction of the current through the wire coils is reversed progressively, so that the magnetic polarity is maintained practically at the same point; therefore there is a continuous pull between this point of the armature core and the poles of the field magnet. The commutator is secured to the armature shaft, and the brushes through which the current enters and leaves are held stationary; keeping this fact in mind, it can be seen at once that in Fig. 12 the current will flow from the brush _a_ through the two sides of the armature wire to brush _b_, hence all the coils on the right of the vertical line will be traversed by the current in the same direction--that is, either to or from the center of the shaft--and in the coils on the left the direction will be opposite, which is just the same order as was explained in connection with Fig. 11.

An electric motor can be turned into an electric generator by simply reversing the direction in which the armature rotates--that is, any electric machine is either a generator or a motor. This fact can be illustrated by means of Figs. 13 and 14, both of which show the armature and the poles of the field magnet. The first figure represents an electric motor, and, as can be seen, the pull between the _N_ pole of the armature and the _P_ pole of the field is in the direction of arrow _b_, hence the armature will rotate in the same direction, as indicated by arrow _a_. To obtain the polarity of the armature and field it is necessary to pass an electric current through both--that is to say, we must expend electrical energy to obtain power from the machine. As soon as the current ceases to flow, the polarity of the armature and field dies out, and the rotation of the former comes to an end. The magnetism, however, does not die out entirely; a small residue is always left, although it is never sufficient to produce rotation, and even if it were it could only cause the armature to revolve through one quarter of a turn. If, after the current has been shut off, the armature shaft is rotated in the reverse direction, as indicated by arrow _a_ in Fig. 14, the motion will be against the pull of the magnetism; therefore, although the poles may be very weak, an amount of power sufficient to overcome their attraction must be applied to the pulley, otherwise rotation can not be accomplished. In consequence of the backward rotation a current is generated in the armature coils, and this current, as it traverses the field coils as well as those of the armature, causes the polarity of both parts to increase. As a result of the increased polarity the resistance to rotation is increased, and more power has to be applied to the pulley. The increase in the strength of the poles results in increasing the current generated, and this in turn further increases the pole strength, so that one effect helps the other, the result being that the current, which starts with an infinitesimal strength, soon rises to the maximum capacity of the machine.

The motor shown in Fig. 10 does not in any way resemble an electric railway motor, nevertheless the principle of action is precisely the same in both. The design of a machine of any kind has to conform to the practical requirements, and this is true of railway motors, just as it is true of printing presses, sawmills, or any other mechanism. A railway motor must be designed to run at a comparatively slow speed and to develop a strong rotative force, or torque, as it is technically called. It must also be so constructed that it will not be injured if covered with mud and water. It must be compact, strong, and light, and capable of withstanding a severe strain without giving out. To render the machine water- and mud-proof it is formed with an outer iron shell, which entirely incases the internal parts. The first railway motors were not inclosed, and the result was that they frequently came to grief from the effects of a shower of mud. When the modern inclosed type of motor, which is called the iron-clad type, first made its appearance it was frequently spoken of as the clam-shell type, and the name is not altogether inappropriate, for while the outside may be covered with mud to such an extent as to entirely obliterate the design, the interior will remain perfectly clean and dry, and therefore its effectiveness will not be impaired.

To enable the motor to give a strong torque and run at a slow speed the number of poles in the field and armature is increased. The design of Fig. 10 has two poles in the field and two in the armature, and is what is known as the bipolar type. Machines having more than two poles in each part are called multipolar machines. The number of poles can be increased by pairs, but not by a single pole--that is, we can have four, six, eight, or any other even number of poles, but not five, seven, or any odd number. This is owing to the fact that there must always be as many positive as negative poles, no more and no less. Railway motors at the present time are made with four poles. The external appearance can be understood from Fig. 15, while Fig. 16 and Fig. 17 will serve to elucidate the internal construction. In Fig. 15 the motor casing is marked _M_, and, as will be seen, it forms a complete shell. The motion of the armature shaft is transmitted to the car-wheel axle _F_ through a pinion, which engages with a spur gear secured to the latter. In Fig. 16 the pinion and gear are marked _N_ and _L_ respectively. As it is necessary that the armature shaft and the axle be kept in perfect alignment, the motor casing _M_ is provided with suitable bearings for both, those for the armature shaft being marked _P P_ in Fig. 16, and one of those for the axle being marked _T_ in Fig. 15. It will be understood from the foregoing that the motor is mounted so as to swing around the car-wheel axle as a center, but, as it is not desirable to have all this dead weight resting upon the wheels without any elasticity, the motor is carried by the crossbars _B B_, Fig. 15, which rest upon springs _s s_ at each end. The beam _A_ and a similar one at the farther end of the _B B_ bars extend out to the sides of the car truck and are suitably secured to the latter. The coils _w w_ are the ends of the field coils and the armature connections, and to these the wires conveying the current from the trolley are connected. The cover _C_ on top of the motor at one end closes an opening through which access to the commutator brushes is obtained. The armature is shown at _H_ in Fig. 16 and the commutator at _K_ in the same figure. Directly under the armature may be seen one of the field magnet coils, it being marked _R_.

As will be noticed in Fig. 16, the motor casing is made so as to open along the central line, and the lower half is secured to the top by means of hinges, _g g_, Fig. 15, and also by a number of bolts, which are not so clearly shown. The gear wheels are also located within a casing, which (Fig. 16) is made so as to be readily opened whenever it becomes necessary. All the vital parts of the machine are entirely covered, and are not easily injured by mud or water.

The construction of the armature and commutator is well illustrated in Fig. 17, which shows this part of the machine by itself. The armature is marked _A_, the shaft _B_, and the commutator _C_. In the diagrams, Figs. 9, 10, 11, and 12, the wire coils are represented as wound upon the surface of the armature core, but, from Fig. 17, it will be noticed that they are located in grooves. A railway motor armature core, when seen without the wire coils, looks very much like a wide-faced cog wheel with extra long teeth, not very well shaped for gear teeth. In Fig. 17 the ends of the teeth are marked _D_, and the grooves within which the wire is wound are marked _E_. The coils are not wound so that their sides are on diametrically opposite sides of the armature core, but so that they may be one quarter of the circumference apart, and, as will be noticed, the wires are arranged so as to fit neatly into each other at the ends of the armature core. The bands marked _F F F F_ are provided for the purpose of holding the wire coils within the grooves. The flanges _H_ and _I_ are simply shields to prevent oil, grease, or even water, if it should pass through the bearings, from being thrown upon the commutator or armature. The pinion through which the armature imparts motion to the car-wheel axle is not shown in Fig. 17, but it is mounted upon the taper end of the shaft.

An electric railway motor is a machine that is characterized by extreme simplicity (there being only one moving part), compactness, and great strength. In addition, as none of the working parts is exposed it can not be injured, no matter how much mud may accumulate upon it. One of the reasons why the electric railway motor has met with such unparalleled success is that it is a machine that can withstand the roughest kind of usage without being damaged thereby. Another reason is that an electric motor can, if called upon, develop an amount of power two or three times greater than its full-rated capacity without injury, providing the strain is not maintained too long. A steam engine or any other type of motor that has ever been used for railway propulsion if loaded beyond its capacity will come to a standstill--that is, it will be stalled--but an electric motor can not be stalled with any strain that is likely to be placed upon it. If the load is increased the motor will run slower and the current will become greater, thus increasing the pull, but the armature will continue to rotate until the current becomes so great as to burn out the insulation. A railway motor calculated to work up to twenty-five-horse power will have to develop on an average about six-or seven-horse power, but if the car runs off the track on a steep grade, and has such a heavy load that the motor is called upon to develop one-hundred-horse power for a few seconds, the machine will be equal to the occasion. This result a steam, gas, or any other type of engine can not accomplish, and it is this fact as much as anything else that has given the electric motor the control of the street-railway field.

[_To be continued_.]

WOMAN’S STRUGGLE FOR LIBERTY IN GERMANY.

BY MARY MILLS PATRICK, PH. D.,

PRESIDENT OF THE AMERICAN COLLEGE FOR GIRLS AT CONSTANTINOPLE.

It is during the latter part of the present century that a general movement has arisen to give women their rights in business life and in political and social affairs. It is the intention of this article to treat of this movement, especially in its relation to education, in Germany, where, of all civilized lands, it has had apparently the smallest results. Progress in the direction indicated has been, however, far greater than appears on the surface, and the movement is slowly taking shape in a form that will gain official recognition and support, and the way is being prepared for scholarly attainments among the women of Germany, superior, possibly, to those of the women of other nations.

There is, moreover, an ideal side to this movement in Germany not altogether found in other lands. The motive for advanced study is more largely joy in the study itself, and desire to supply the spiritual needs of an idle life. In order to understand this ideal tendency it is necessary to cast a glance backward over nearly three hundred years.

Let us begin with the contest which was waged so successfully for the development and protection of the German language, first against the Latin and later against the French. In this struggle women took a prominent part, especially through membership in the society called the “Order of the Palms,” which, before the beginning of the Thirty Years’ War, united the strongest spirits of Germany for this purpose. The first woman to join this society was Sophie Elizabeth, Princess of Mecklenburg, married in 1636 to the Herzog of Braunschweig. She was followed by many others, both of the nobility and the common people, and was named by virtue of this leadership “The Deliverer.”

In the eighteenth century we have the founder of the German theater, Caroline Neuber. In the artistic sense she was the first director of the German stage, the first to turn the attention of the greatest actors of her day to the ideal side of dramatic presentation. Early in the eighteenth century women began to take up university studies. A certain Frau von Zingler received a prize from the University of Wittenberg for literary work, and the wife of Professor Gottscheds entered upon a contest for a prize in poetry with her husband.

We find some old verses published in Leipsic, in a book of students’ songs, in 1736, recognizing the fact that women attended lectures in the university there, although the reference is rather sarcastic, speaking of “beauty coming to listen in the halls of learning.”

In 1754 the first woman received her degree of Doctor of Medicine in Halle--Dorothea Christine Erxleben, _née_ Leborin, a daughter of a physician, who attained to this result only after many years of painstaking effort. With her father’s help she studied the classics and medicine, and gradually, in spite of the objections of his brother physicians, began to practice as a doctor under her father’s protection. She is said to have cured her patients _cito tuto_, _jucunde_, and in 1742 she published a book on the right of women to study, the title of which, according to the custom of the day, included the full table of contents. This book passed through two editions, and enabled her to gain the attention of Frederick II, who was persuaded to order the University of Halle to grant her the privilege of taking her examination there. The day arrived, and the hall was crowded for the occasion; the candidate passed the ordeal in a brilliant manner, and took the oath for the doctor’s degree amid a storm of applause from the listeners present.

In the present century the germ of the movement for educational rights for women came into consciousness in Germany in the stormy year 1848, and first found expression and life through the work of two women--Louise Otto Peters and Auguste Schmidt. The former founded the Universal Association for Women in Germany, and through this society both these women worked for thirty years and did much toward preparing the way for the broader efforts of the present time.

It is a fact granted by all the educational world that scholarship attains a depth and thoroughness in Germany not found in other lands, and this very perfection has been in part the cause of the backwardness of the educational movement among the women, for a high degree of scholarship has often been acquired by the men at the expense of the devoted service of the women connected with them. Yet when the women of Germany demand their educational rights it will be to share also in the rich intellectual inheritance of their land.

The majority of the men thus far regard the movement with distrust and suspicion, but are powerless to crush it out. An amusing instance occurred last year in the family of an official in one of the large university towns. He was a conservative man who had his immediate family in a proper state of subjection, but his mother-in-law, alas! he could not control, and to his dismay she enrolled herself at the university as a _Hospitant_, and, in spite of the protestations of her son-in-law, she was a regular attendant upon the courses of lectures that she had elected.

The regular schools for girls in Germany, above the common schools attended by girls and boys together, are of two grades--the middle schools and the high schools. The avowed object of these schools is to fit girls for society and for the position of housewife, as Herr Dr. Bosse, the Minister of Public Instruction for the German Empire, states in his report on the condition of girls’ schools in Germany, and as he publicly declared before the German Parliament in the discussion regarding the establishment of a girls’ gymnasium in Breslau, referred to later on in this paper.