Chapter XXXV: Operation of Motors

In operating motors of any considerable size, whether connected to the public supply mains of a central generating station for combined lighting and power service, or to power service mains only, there are certain precautions to be observed in starting, stopping, and regulating the motor, in order that the efficiency of the supply, and indirectly the working of other motors and lamps connected to the mains in the immediate neighborhood, may not be affected by abnormal variations of pressure. These precautions should be observed also to prevent any danger of the motor itself being subjected to detrimental mechanical shocks and excessive temperatures in the working parts.

Before Starting a Motor.--The general instructions relating to inspection and adjustment, lubrication, etc., which have already been given, should be carefully followed preparatory to starting[E].

[E] NOTE.--In starting a motor, first see that the bearings contain sufficient oil and that the brushes bear evenly on the commutator. If a circuit breaker be used, close it; then close the main switch. Rotate slowly the handle of the starting rheostat as far as it will go. Care should be taken, in starting the motor, that the handle of the rheostat be not rotated too fast. To stop a motor, open the circuit breaker or switch, which will cut in the resistance of the starting box. Never attempt to stop a motor by forcibly pulling open the starting box, _Disregard of these instructions may cause burning out of the field coils._

Starting a Motor.--In starting a motor, resistance must be put in series with the armature because, since there is no reverse electromotive force to counteract the applied voltage when the motor is at rest, the switching of the latter direct to the motor would result in an abnormal rush of current. This, in addition to being uneconomical and productive of a drop of voltage in the mains, would injure all except the smallest motors. Hence motors above two horse power usually require a rheostat.

Ques. Describe a rheostat or "starting box."

Ans. It consists essentially of a suitable resistance to be inserted at starting to reduce the initial rush of current, and which can be cut out in sections by successive movements of a lever as the speed increases.

Ques. Describe what occurs in starting a motor.

Ans. When the lever of the starting box is moved to the first contact some of the resistance is cut out of the circuit and current flows through the motor. This produces a torque and starts the armature rotating. The movement of the armature induces a reverse voltage, which, as the speed increases, gradually reduces the applied current. With this reduction of current, the torque is reduced and the speed not accelerated as quickly as at first. When the applied current has been reduced to a certain value by the increasing reverse current, the handle of the starting box is moved to the next contact, and so on till all the resistance in the starting box has been cut out, the motor then attaining its normal speed.

Ques. What is the difference between a starting box and a speed regulator?

Ans. Motor starting rheostats or "starting boxes," are designed to start a motor and bring it gradually from rest to full speed. They are _not_ intended to regulate the speed and must not be used for such purpose.

_Failure to observe this caution will result in burning out the
resistance which, in a motor starter, is sufficient to carry the
current for a limited time only_, whereas in the case of speed
regulators sufficient resistance is provided to carry the full load
current continuously.

Ques. For what kinds of service are speed regulators used?

Ans. In cases when the speed must be varied, as in traction motors, organ blowers, machine tool drive, etc.

Ques. How long does it take to start a motor?

Ans. Usually from five to ten seconds.

Ques. How is the starting lever operated?

Ans. It is moved progressively from contact to contact, pausing long enough on each contact for the motor to accelerate its speed before passing to the next.

Ques. What are the conditions at starting in a series motor?

Ans. There is a rush of current, the magnitude of which depends on the amount of resistance cut out at each movement of the starting lever.

Ques. How are small series motors started on battery circuits?

Ans. By simply closing a switch to complete the circuit, the resistance of the battery being sufficient to prevent a great rush of current while starting.

Ques. How is a shunt motor started?

Ans. In starting a shunt motor, no trouble is likely to occur in connecting the field coils to the circuit. Since the resistance of the armature is very low, it is necessary on constant voltage circuits to use a starting rheostat in series with the armature.

The necessary connections are shown in fig. 756. The switch is first
closed thus sending current through the field coils, before any
passes through the armature. The rheostat lever P is then moved to the
first contact to allow a moderate amount of current to pass through
the armature. The resistance of the rheostat is gradually cut out by
further movement of the lever P, thus bringing the motor up to speed.

Ques. How does the reverse voltage affect the starting of a motor?

Ans. When a motor is standing still, there is no reverse voltage, and the current taken at first is governed principally by the resistance of the circuit. If the motor be series wound, there is a momentary reverse voltage, due to self-induction while the field is building up. If the motor be shunt wound, self-induction delays the current through the field coils, but that through the armature is not impeded by such cause. When the armature begins to revolve, reverse voltage is developed which increases with the speed. The resistance of the starting box may be gradually cut out as the armature comes to speed. Thus the reverse voltage gradually replaces ohmic drop in limiting the current as the motor comes to speed.

Fig. 742.--Compound starter. Rheostats designed for the double duty of starting a motor and regulating its speed are commonly known as compound starters, the resistance provided being a combination of armature resistance for starting duty and shunt field resistance for speed regulation.]

Failure to Start.--This fault, which is liable to occur in a motor of any description, is similar to failure to excite in a dynamo, and is liable to be produced by any of the causes mentioned in connection with the latter fault, excluding insufficient speed, and insufficient residual magnetism.

When a motor fails to start, it should first be ascertained if a supply of electrical energy be available in the mains. This may readily be discovered by means of a voltmeter, or if low tension service, by means of the fingers bridging across the main terminals. If the supply of energy be present, the contact arm of the starter should be moved into such position that all resistance is inserted into circuit with the motor. This is important, as the motor may start suddenly while trying to ascertain the cause of the stoppage.

Having closed the switch, if the motor fail to start, it will be advisable to remove the load if possible, as the failure may arise from an overload of the machine. This being effected and the motor not starting, the terminals of the latter should be tested by the means already described for voltage. If no voltage be generated, a broken circuit or a defective contact may be looked for in the main fuse, switch, or starting box. The resistance coils of the latter, through the heat developed, frequently break in positions out of sight. If a defective contact of this nature cannot readily be seen, the contact arm should be moved slowly over the contacts, as it is possible the broken coil may be cut out of circuit by this means.

If a difference of pressure exist between the motor terminals, the
field magnets will, if shunt or compound wound and in good order,
be excited, which may be ascertained by means of a bar of iron. If
no magnetism be present, it will of course, indicate a broken or
bad connection, either between the terminals of the field coils, or
one or more of the coils themselves. If the bar pull strongly, the
position of the brushes upon the commutator in regard to the neutral
points should be ascertained, and the rocker adjusted, if necessary,
to bring them into their correct positions. If this fail to start the
motor, the connecting leads from the motor terminals to the brushes
and the brushes themselves should be carefully examined for broken
or bad connections, and defective contact of the brushes with the
commutator. In the latter case, it may arise from a dirty state of
the commutator, or from the brushes not being fed properly. If due
to these causes, pressing the brushes down upon the commutator with
the fingers will probably start the motor. If the failure to start
arise from none of these causes, it is probably due to the field coils
acting in opposition, or to a short circuited armature. This latter
remark applies more especially to motors provided with drum armatures.

Precautions with Shunt Motors.--With motors of this type, because of the large amount of self-induction in the shunt windings, it is important to note: 1, that in switching on the field magnet, the current may take an appreciable time to grow to its normal value, and 2, that in switching off, especially with quick break switches, high voltages are induced in the windings, which may break down the insulation.

Fig. 750.--Monitor automatic starter, equipped with relay for push button control.]

Ques. What provision is made so that the magnetizing current will have time to reach its normal value?

Ans. The field connections are generally separated from the actual starter, and taken to the main switch, so that wherever the main switch is closed, the current flows through the field coils, before the starting lever is moved.

Ques. How are the connections arranged to avoid excessive voltage in the windings due to self-induction?

Ans. Generally the armature and field magnet circuits are placed in a closed circuit that is never opened.

In other cases, in order that the rise of voltage may not injure the
insulation when the shunt is opened, a special form of main switch
is sometimes used which, before breaking from the supply, puts a
non-inductive resistance across the shunt of the motor. This is known
as a _flashing resistance_.

Ques. How can shunt motors be controlled from a distant point?

Ans. The starter and switch are placed at the desired point and the two main wires and the field wires run from that point to the motor.

This requires additional wire which increases the cost and line loss.

Regulation of Motor Speed.--Motors are generally run on constant voltage circuits. Under these conditions, the speed of series motors varies with the load and at light loads becomes excessive. Shunt motors run at nearly constant speeds.

For many purposes, particularly for traction, and for driving tools, it is desirable to have speed regulation, so that motors running on constant voltage circuits may be made to run at different speeds.

The following two methods are generally used for regulating the speed of motors operated on constant voltage circuits:

1. By inserting resistance in the armature circuit of a shunt wound motor;

2. By varying the field strength of series motors by switching sections
of the field coils in or out of circuit.

Ques. Describe the first method.

Ans. This method is illustrated in fig. 756. When the main switch is closed, the field becomes excited, then by moving the lever P of the starting rheostat the various contacts (1, 2, 3, 4, 5), more or less of the rheostat resistance is cut out of the armature circuit, thus varying the speed correspondingly.

This is the same as the method of starting a motor, that is, _by
variation of resistance in armature circuit_, but it should be
noted that when this method is used for speed regulation, _a speed
regulating rheostat should be used instead of the ordinary starting
box_, because the latter, not being designed for the purpose, _will
overheat and probably burn out_.

Ques. Describe the second method.

Ans. This method of regulating the speed of a series motor is shown in fig. 757. The current through the armature will flow through all the field windings when the position of the switch lever S, is on contact 4, and the strength of the field will be the maximum. By moving the arm to contact 3, 2, etc., sections of the field winding are cut out, thus reducing the strength of field and varying the speed.

Ques. How does the speed vary with respect to variation of field strength?

Ans. Decreasing the field strength of a motor increases its speed, while increasing the field strength decreases the speed.

Under the conditions of maximum field strength, as with switch S on
point 1, the torque will be greatest for any given current strength
and the reverse voltage also greatest at any given speed. The current
through the armature of the motor, to perform any given work, will
thus be a minimum, as well as the speed at which the motor has to run,
in order to develop sufficient reverse voltage to permit this current
to flow. Regulation of speed by varying the field strength is limited
in range of action, since the field saturation point is soon reached,
moreover, with too low a field strength, armature reaction produces
excessive field distortion, sparking, etc.

Ques. How is the speed of shunt and compound motors varied with respect to the normal speed in the two methods?

Ans. The first method (variable resistance in armature circuit) reduces the speed _below_ the normal or rated speed of the machine, while the second method increases the speed _above_ the normal.

In the first method the amount of speed reduction depends partly upon
the amount of resistance introduced into the armature circuit, and
partly upon the load.

In the second method the amount of speed increase depends entirely
upon the amount of resistance placed in the shunt winding circuit.

Eighty-five per cent. is about the maximum speed reduction obtainable by armature resistance but so great a reduction is seldom satisfactory since comparatively slight increases in the load will cause the motor to stall.

Shunt field regulation may be obtained up to any point for which the
motor is suited, the only limitation in this case being the maximum
speed at which the motor may be safely operated.

It should be remembered, however, that speed increase by shunt field
weakening increases the current in proportion to the increase in
speed, and care should be taken not to overload the armature.

NOTE.--A compound motor may be made to run at constant speed, if
the current in the series winding of the field be arranged to act in
opposition to that of the shunt winding. In such case, an increase
of load will weaken the fields and allow more current to flow through
the armature without decreasing the speed of the armature, as would be
necessary in a shunt motor. Such motors, however, are not very often
used, since an overload would weaken the fields too much and cause
trouble. If the current in the series field act in the same direction
as that in the shunt fields, the motor will slow up some when a heavy
load comes on, but will take care of the load without much trouble.

NOTE.--Motors have much the same faults as dynamos, but they make
themselves manifest in a different way. An open field circuit will
prevent the motor starting, and will cause the melting of fuses or
burning out of the armature. A short circuit in the fields, if it cut
out only a part of the winding, will cause the motor to run faster and
very likely spark badly. If the brushes be not set exactly opposite
each other, there will also be bad sparking. If they be not at the
neutral point, the motor will spark badly. Brushes should always be
set at the point of least sparking. If it become necessary to open the
field circuit, it should be done slowly, letting the arc gradually
die out. A quick break of a circuit in connection with any dynamo,
or motor is not advisable, as it is very likely to break down the
insulation of the machine. The ordinary starting box for motors is
wound with comparatively fine wire and will get very hot if left in
circuit long. The movement of the arm from the first to the last point
should not occupy more than thirty seconds and if the armature do not
begin to move at the first point, the arm should be thrown back and
the trouble located.

Ques. How is a wide range of speed regulation secured?

Ans. By a combination of the two methods.

Regulation by Armature Resistance.--Speed regulators for this method of regulation, are designed to carry the normal current on any contact without overheating and when all the resistance is in the circuit, they will reduce the speed of the motor about 50 per cent. provided the motor be taking the normal current. When operating without resistance in the armature circuit, shunt wound and compound wound motors will regulate to approximately constant speed regardless of load. This characteristic of inherent regulation is lost, however, when armature resistance is employed to reduce the speed of the motor, fluctuations in load resulting in fluctuations in speed, which become more noticeable as the amount of resistance inserted in the armature circuit is increased. Accordingly, it becomes necessary to move the lever of the speed regulator forward or backward to again obtain the speed at which the machine was operating before the load changed.

When the speed of a motor driving a constant torque machine is
reduced by inserting resistance in the armature circuit there is
no corresponding reduction in current consumed. The motor runs more
slowly simply because a part of the energy impelling it is shunted
into the resistance and there dissipated in the form of heat. Hence,
whether the motor be operating at full speed or half speed, the amount
of current consumed is the same; the only difference being that in the
one case all the energy taken from the line is expended in driving the
motor while in the other case only one half is utilized for power,
the other half being dissipated in the resistance. Speed regulation
by armature resistance only is therefore open to two objections:
1, the difficulty of maintaining constant speed under varying load
conditions, and 2, the necessity of wasting energy to secure speed
reduction. These objections are, in part, offset by the fact that
speed reduction by armature resistance may be applied to any motor of
standard design and requires nothing more than the simplest and least
expensive speed regulating rheostat.

In cases where the motor will be operated nearly always at full speed,
the difference in first cost of the installation may justify the
use of the armature resistance method of control. As a rule, speed
regulation by shunt field resistance is preferable.

Regulation by Shunt Field Resistance.--Since regulation by this method is for speeds above normal, a starter must be used to bring the motor up to its rated speed. Usually the starter is combined with the regulator, as shown in fig. 761, the device being called a _compound starter_.

LOCATION AND SETTING.--The motor should be placed in as cool, clean and well ventilated a location as possible, away from acid or other fumes which would attack the metal parts or insulation, and should be easily accessible for cleaning and oiling. Do not put it in some corner where care of motor will be neglected because of the trouble of getting at it. The motor should be set so that the shaft is level and parallel with the shaft it is to drive so that the belt will run in the middle of the pulleys. Do not use a belt which is much too heavy or too light for the work it has to do, as it will materially reduce the output of the motor. The belt should be about one-half inch narrower than the pulley.

ROTATION.--In order to reverse the direction of rotation, interchange leads A and B, and shift brush ring as shown in the diagram above.

SUSPENDED MOTORS.--Motors with ring oil bearings may be used on the wall or ceiling by taking off end caps and revolving 90 or 180 degrees until the oil wells come directly below the bearings.

STARTING.--Before starting the motor see that the armature revolves freely, that the bearings are full of oil, and the oil rings are in place and free to turn.

Examine connections carefully to see that they are according to above diagram, after which proceed as follows:

1. Close the main knife switch. This action should not allow any current
to pass through the motor (see Note 2);

2. Move the lever of the starting rheostat quickly and squarely onto the
first segment, and hold it there for about a second;

3. Move the lever to the second segment and hold it there for about a
second;

4. Move the lever to the third segment and hold it there for about a
second, and so on from one segment to the next until the lever has
been moved over all the segments to the short circuit position,
where it should be held firmly by the retaining magnet.

If the motor do not start when the lever of the starting rheostat is on the third segment, open the main knife switch and look for the trouble. This may consist of any of the following:

a. Wrong connections;

b. Too great a load on the motor;

c. The motor brushes not in proper position;

d. An open circuit of some kind;

e. A short circuit of some kind.

NOTE 1.--It is always advisable, in case of trouble, to make sure that the fields of the motor are magnetized. This test is easily made by first closing the main knife switch, then moving the lever of the starting rheostat to the first segment, and finally having an assistant place a screw driver or other piece of iron against the pole pieces of the motor. If the fields be magnetized, a heavy pull on the iron should result.

NOTE 2.--Any possibility of arcing on the first contact of the starting rheostat when starting can be obviated by _first_ moving the lever onto the initial contact, holding it there, and then closing the main line switch, after which proceed as per paragraphs 3 and 4.

TO STOP THE MOTOR.--Open the main knife switch and let the starting rheostat take care of itself. The lever will not fly back immediately, but will hold until the motor has slowed down considerably.

NOTE.--The above directions apply only to starters of the sliding contact type.

TEMPERATURES.--If located as instructed above, these motors will carry full load as indicated on the name plate on the motor with a temperature rise of not over 40 degrees Centigrade, or 75 degrees Fahrenheit above the surrounding air. This will feel hot to the hand but is far below the danger point. If the motor feel too hot, get a thermometer and measure the temperature. To do this, place the bulb of the thermometer for 10 minutes against the frame, cover with a cloth or piece of waste, and note temperature as compared with that of room. If the motor run in a small, enclosed space with no ventilation, the temperatures will be somewhat higher than those given above.

OILING.--Fill the oil wells to the overflow before starting and keep them full. Use good "dynamo oil." Be sure that the oil rings turn freely while the motor is running. If in a dirty place, draw off the old fluid and fill with new every two or three months.

CARE OF MOTOR.--The motor must be kept clean. If the commutator become rough, smooth it up with No. 00 sandpaper moistened with oil. When fitting new brushes or changing them, always sandpaper them down until they fit the commutator perfectly, by passing to and fro beneath the brush a strip of sandpaper, having the rough side toward the brush.

Brushes must _always_ be renewed before the metal of the holder comes in contact with the commutator.

Don't use anything on commutator except good mineral machine oil, or kerosene, and this only in very small quantities applied with a cloth having no lint or threads.]

The weakening of the shunt field of a motor by the insertion of resistance in the shunt field circuit causes the armature to revolve more rapidly. One advantage of this method of control is that the motor will inherently regulate to approximately constant speed under widely varying load conditions. Another advantage is found in the fact that all of the current taken from the line is utilized for power, the changes in speed being obtained not by dissipating a portion of the effective energy in the resistance (as in the case of the armature resistance method of control) but by weakening the reverse voltage by inserting resistance in the shunt field circuit. Speed increase by shunt field weakening is limited, however, to about 10 to 15 per cent. above the normal speed in motors of standard construction. Greater ranges of speed can be obtained from motors especially designed for shunt field control but should not be attempted with motors of standard design without first ascertaining from the manufacturer the maximum safe speed.

Combined Armature and Shunt Field Control.--Regulation by combined armature and shunt field resistance is by far the easiest way of obtaining a wide range of speeds. Rheostats embodying these methods are known as _compound speed regulators_, one form being shown in fig. 762. Standard regulators can be obtained giving a wide range of speed variation, and special regulators may be constructed giving practically any desired range.

Selection of Starters and Regulators.--Unsatisfactory operation of these devices is, in nearly all cases, due to lack of precaution in selecting the proper piece of apparatus for the work to be done. One of the commonest errors is to select a rheostat of insufficient capacity. If the current required to operate the motor at full speed with no resistance in circuit be greater than the rated capacity of the rheostat, overheating of the resistance will result. An increase in temperature even to a point where the hand cannot be held on the enclosing case need cause no apprehension, but should the resistance become red hot it indicates that the apparatus is being worked far beyond its capacity, and the load on the motor should be reduced or a regulator of greater capacity substituted.

If the current required to operate the motor at full speed with no resistance in circuit be less than the rated capacity of the rheostat no overheating will occur, but it will not be possible to secure the full 50 per cent. speed reduction the rheostat is designed to give with all resistance in circuit.

In ordering a starter or regulator, the manufacturer should be furnished with the following information:

1. Horse power of motor with which speed regulator will be used;

2. Voltage of motor;

3. Winding of motor, whether series, shunt, or compound wound;

4. Nature of the machine which motor is to operate;

5. Normal rated speed of motor to be used;

6. Maximum speed at which it is desired to operate the motor;

7. Minimum speed at which it is desired to operate the motor;

8. Whether controller will ever be required to reverse direction of
motor or to operate it in one direction only;

9. If reversible controller be desired, whether or not full range of
speed control is required in both directions;

10. Whether the regulator shall be equipped with any of the following
devices: no voltage release, overload release, knife switch, fuses;

11. Whether button contacts or renewable contact segments are preferred;

12. Giving, also, if possible, the resistance of the shunt field
cold, and the shunt field current at the maximum speed required.
If this cannot be ascertained, give horse power, voltage, normal
speed, maximum speed required, serial number of motor and name of
manufacturer.

Speed Regulation of Traction Motors.--The speed regulator for motors of this class is called a _controller_, and being located in an exposed place is enclosed in a metal casing. Controllers are designed to be used for starting, stopping, reversing, and regulating the speed of motors where one or more of these operations have to be frequently repeated.

The controller used with a single motor equipment is practically
the same as any other single motor starting box, excepting that
the resistance has sufficient carrying capacity to be left in the
circuit some time. When the motor is to operate at full speed all the
resistance is cut out. To reverse, a reversing notch is placed in the
armature or field circuit, but not in both.

Ques. What provision is made to overcome the arc when the circuit is opened?

Ans. A magnetic field is used with such polarity that it blows out the arc.

Magnetic blow out coils are used on all controllers designed for 500
volt circuits, and on types designed for lower voltages requiring more
than 60 amperes normal capacity.

The coils are wound with either copper wire or flat strips of
sufficient capacity to carry full load current continuously without
undue heating, and after being wound they are treated with an
insulating compound making them moisture proof.

Ques. What provision is made to prevent reversal before bringing the controller lever to the "off" position?

Ans. Controllers having separate reversing cylinders are fitted with mechanical interlocks making it necessary to place lever in off position before reversing.

Two Motor Regulation.--With a two motor equipment, the controller becomes more complicated because it must be arranged to switch the motors in series or in parallel, so as to secure economy at half and full speed. The various connections of series-parallel regulation are shown in figs. 772 to 782.

From these diagrams it is seen that the motors are first operated in
series until all the resistance is cut out by the controller (figs.
772 to 777).

The next point on the controller puts the two motors in parallel
with some resistance in the circuit (fig. 778), which resistance is
gradually short circuited on the remaining controller points, until
at full speed all the resistance is cut out, the two motors remaining
in parallel (figs. 778 to 782).

Stopping a Motor.--If it be desired to stop a motor, the main switch is opened. As the armature of the motor continues to operate, due to its inertia, it generates an electromotive force which sends a current through the shunt connected field circuit and helps to maintain the field excitation. When the speed of the motor has decreased sufficiently so as not to endanger the motor should the main switch be thrown, the current in the series magnet becomes weakened, and the spring throws back the starting box arm.

It should be noted that in stopping a motor having a starting box provided with a no voltage release simply open the main switch and do not touch the lever because otherwise, the self induced voltage of the field circuit may puncture the field winding or the insulation of the adjoining wires in the starting box.

HAWKINS PRACTICAL LIBRARY OF
ELECTRICITY
IN HANDY POCKET FORM PRICE $1 EACH

_They are not only the best, but the cheapest work published on
Electricity. Each number being complete in itself. Separate numbers
sent postpaid to any address on receipt of price. They are guaranteed
in every way or your money will be returned. Complete catalog of
series will be mailed free on request._

ELECTRICAL GUIDE, NO. 1

Containing the principles of Elementary Electricity, Magnetism,
Induction, Experiments, Dynamos, Electric Machinery.

ELECTRICAL GUIDE, NO. 2

The construction of Dynamos, Motors, Armatures, Armature Windings,
Installing of Dynamos.

ELECTRICAL GUIDE, NO. 3

Electrical Instruments, Testing, Practical Management of Dynamos
and Motors.

ELECTRICAL GUIDE, NO. 4

Distribution Systems, Wiring, Wiring Diagrams, Sign Flashers,
Storage Batteries.

ELECTRICAL GUIDE, NO. 5

Principles of Alternating Currents and Alternators.

ELECTRICAL GUIDE, NO. 6

Alternating Current Motors, Transformers, Converters, Rectifiers.

ELECTRICAL GUIDE, NO. 7

Alternating Current Systems, Circuit Breakers, Measuring
Instruments.

ELECTRICAL GUIDE, NO. 8

Alternating Current Switch Boards, Wiring, Power Stations,
Installation and Operation.

ELECTRICAL GUIDE, NO. 9

Telephone, Telegraph, Wireless, Bells, Lighting, Railways.

ELECTRICAL GUIDE, NO. 10

Modern Practical Applications of Electricity and Ready Reference
Index of the 10 Numbers.

Theo. Audel & Co. Publishers 72 FIFTH AVENUE, NEW YORK