170 
SCIENCE. 
AN IMPROVED ELECTRO-MOTOR* 
By Theodore Wiesendanger. 
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 (e. 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 of 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 a long time past clung to 
the idea that the efficiency of an electro-motor — or the 
amount of energy r to be obtained from such a machine by 
means of a current of given strength circulating in the coils 
of its armature only' — bears 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- 
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 g of the armature only' approaches the pole A of 
the field-magnets while moving from r to if, 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 are 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- 
trates a machine in which the armature during nearly the 
whole of its motion either approaches to or recedes from 
*A paper read before the British Association. 
