170 



SCIENCE. 



AN IMPROVED ELECTRO-MOTOR.* 

 By Theodore Wiesend.ynger. 



While recently many minds have been at work, with more 

 or less of success, to produce improvements in dynamo- 

 generators of electric energy, very few have given their 

 special care and attention to the development of the elec- 

 tro-motor. Experience has taught us hitherto that the effi- 

 ciencies of one and the same machine for action and reac- 

 tion, or for use either as a generator, or by the inverted 

 process as an electro-motor, stand in a certain and direct 

 proportion to each other, or that our most efficient genera- 

 tors, such as the Siemens, Brush and Gramme, machines 

 prove also the most effective motors, and on the other hand 

 that inferior dynamo-machines invariably are inefficient 

 motors. It would, however, be hazardous to conclude from 

 these results that this rule should hold good for all future ma- 

 chines, and from the results of researches I have recently 

 made, I come to the conclusion that the motors which are to 

 supersede those now in use could not be employed as gen- 

 erators. Dynamo-machines, such as now constructed, only 

 prove efficient when their field-magnets are able to retain at all 

 times (^. g., even when the machine stands at rest) a certain 

 and very considerable amount of residual magnetism, and 

 for that reason their cores are made oi retentive material, 

 hard cast iron, as is the case in the Brush and Gramme ma- 

 chines ; or if the cores consist of soft iron they are attached 

 to large masses of hard cast iron, in such a manner that the 

 latter are inclosed in the magnetic circuit, and form part of 

 the cores. 



Generators of the same kind, when made small in size, 

 have cores much larger and heavier in proportion, and, 

 moreover, the baseplate, or, as in the Weston machine, a 

 heavy retentive cylinder, is made to form a portion of the 

 field-magnets. But all efforts hitherto made to produce 

 efficient small dynamo-machines with cores of soft iron 

 only, have resulted in absolute failure, although men of the 

 highest genius have made repeated and prolonged efforts 

 to solve that most difficult of problems. 



These curious facts conclusively prove that the theory 

 explanatory of the action of dynamo-machines, as now uni- 

 versally adopted, viz., the theory of inductive action and 

 reaction between the field-magnets and the armature, can- 

 not any longer be considered complete or satisfactory ; for 

 even wrought iron, especially when occurring in large 

 masses, always contains an appreciable amount of residual 

 magnetism, more especially after it has once been subjected 

 to strong magnetization, and if the above theory were cor- 

 rect and complete, then the smallest possible amount of 

 residual magnetic energy, augmented by repeated action 

 and reaction, would be sufficient for the starting of such a 

 machine to action. This, however, experience proves not 

 to be the case, and the theory, although stoutly adhered to, 

 must be either abandoned or amended. 



The inventors of the most recent electro-motive engines 

 have worked — perhaps unconsciously — upon the idea that 

 the construction and action of electro-motors are based al- 

 together upon the same laws as those of dynamo or mag- 

 neto machines, and, in accordance with that assumption, 

 the field-magnets of the Desprez motor are made to consist 

 of large and heavy masses of magnetized steel. 



Experimenters have also for along time past clung to 

 the idea that the efficiency of an electro-motor — or the 

 amount of energy to be obtained from such a machine by 

 means of a current of given strength circulating in the coils 

 of its armature only — hears a definite and direct proportion 

 to the magneto-inductive power of its field-magnets, and 

 that an increase of power in the field-magnets alone must 

 necessarily produce greater capabilities of the machine. 



This, however, is a mischievous theory, because erron- 

 eous in its very principles, and development would only 

 lead to the hypothesis of perpetual motion. On the con- 

 trary, starting from the consideration of the fact that a very 

 small magnetic needle, if acted upon by one of the poles of 

 another and very powerful magnet, has its polarity des- 



*A paper read before the British Association. 



troyed or reversed, and that if one of its poles, say the N 

 pole, is presented to a similar (N) pole of the large mag- 

 net, the former will instantly lose its characteristic qualities 

 and be attracted by its overpowering opponent, we can only 

 come to the one rational conclusion that the power or the 

 field-magnets of an electro-motor, as compared to that 

 of the magnet or magnets constituting its armature, 

 should not surpass the limit of some certain ratio, to be 

 determined yet by experiments carefully conducted, and 

 that, if it surpasses the limit, the capabilities of the ma- 

 chine must be impaired. Acting on this principle, I have 

 constructed a motor in which the power of the field mag- 

 nets is as nearly as possible equal to that of an armature, the 

 core of the former being very light and made entirely of 

 soft iron ; and the satisfactory results obtained from this 

 machine are a sure sign that further investigation of the 

 subject and experiments made with a view of determining 

 the exact ratio of power between the magnets and armature 

 will result in further improvement. 



Another and very important consideration in the con- 

 struction of dynamo-machines and electro-motors has 

 not yet received that care and attention from scientific in- 

 vestigators which would lead to immediate progress. It is 

 the method of motion of the revolving armature with regard 

 to its approaching to, or receding from the poles of the field- 

 magnets. In nearly all the machines now constructed the 

 polar faces of the cores of the field-magnets and those of the 

 armature are of such a shape, and the latter is caused to re- 

 volve in such a manner, that only in a small portion of 

 the revolution its poles either approach the poles 

 of the field-magnets or recede from them. But the most 

 successful production of induced currents will be achieved, 

 and the greatest amount of power will be derived from a 

 motor, if attention is paid not merely to the one condition, 

 that the armature should revolve in the most highly con- 

 centrated magnetic field possible, but also that nearly the 

 entire motion of the revolving armature should be either 

 one of approach or of withdrawal. Let us first of all con- 

 sider the case of a machine with two poles only of field- 

 magnets and two poles of the revolving armature. 



It is usual to give the active faces of the former such a 

 shape that a section of the same represents a portion of a 

 true circle. See Fig. 7. 



In the ordinary machines now in use the radius of the 

 circle described by the outline of the revolving armature, 

 and that of the larger circle described in portion by the sec- 

 tion of the inner or active faces of the poles are nearly the 

 same, and the two circles are concentric. (See Fig. 7.) 

 The pole^ of the armature only approaches the pole A of 

 the field-magnets while moving from c to d, or where the 

 intensity of the magnetic field of A is at its minimum. 

 When continuing its motion from d to rand to/, the pole 

 g can no longer be said to approach A, because the dis- 

 tance between the respective surfaces remains constant. 



I therefore propose that the devices shown in Figs. 9 and 

 6 should be adopted. The radius of the circle, part of 

 which is formed by the section d, r, c, is considerably 

 larger than that of the circle described by the outline of 

 the field of motion of the armature ; d, r, c is, moreover, 

 considerably less than the half of a circle and the three 

 circles d, r, c, f, e, h, and that described by the outline of 

 the field of motion of the armature are not concentric. The 

 pole^- of the armature, when in motion, approaches the 

 pole, A, not only in its course from e to C, but also when 

 in the most intense magnetic field of A, viz., whilst moving 

 from C to z and d. Fig. 11 represents a section of the field- 

 magnet's cones E F and G H, and pole's pieces N and S cast 

 in two halves and mounted on a base board, to which they 

 are fixed by the two bolts R and T. The same principles 

 may be applied to machines with field-magnets of more 

 than two poles (see Fig. 3) ; or the armature itself may be 

 made of such a shape as to work under the conditions 

 above stated (Fig. 4). But even if the poles of the arma- 

 ture and those of the field-magnets arc of the ordinary 

 shape, a machine with more magnets will be more perfect 

 in its action than one with two poles only. Fig. 10 illus- 

 tiates a machine in which the armature during nearly the 

 whole of its motion either approaches to or recedes from 



