Receiving Apparatus.

THE VARIOMETER.

A variometer is a tuning device in which two coils of wire are placed in series and connected so that the turns can be made to oppose one another. One coil is movable and by turning it the currents flowing through the adjacent coils oppose each other and decrease the self-induction of the whole and consequently the period of the circuit.

Fig. 161. Variometer.

The accompanying illustration shows the constructive details of an efficient form of variometer.

The coils are wound around two cardboard cylinders. One cylinder is 6 inches in diameter and the other 5 inches. Both are 2 inches long. The large cylinder is wound with twenty-five turns of No. 22 B. S. gauge single silk covered wire wound in two sections so as to leave a space 3/8 inch wide in the center. The small cylinder is wound in the same manner with the same size of wire but contains thirty turns so as to make the length of wire in each of the coils practically equal.

The space in the center of each of the coils allows a supporting rod to pass through without interfering with the wire. The shaft is a piece of 5/16 brass rod about 7 1/2 inches long. The upper end is provided with a knob and a pointer. The large coil is mounted on the under side of a wooden cover made to fit a containing case of the proper size to receive the variometer and of a style similar to that ordinarily used to enclose a variable condenser.

The shaft passes through the larger coil, at two points diametrically opposite, but should not fit tightly. It also passes through the smaller coil but is fastened to the latter by means of a cross bar so that when the knob is turned the coil will revolve also. The coils are connected by means of a piece of braided wire or flexible conductor, long enough so as not to interfere with the movement of the inner coil.

The outside terminals of the coils terminate in binding posts mounted on the top of the case. When making a variometer be careful not to employ any iron or steel in its construction, not even iron screws.

The variometer is placed in the receiving circuit by connecting it in series with the aerial before it reaches the tuning coil or loose coupler.

NEW CRYSTAL DETECTORS.

Silicon Detector.—The silicon detector is always interesting because it was one of the first mineral rectifiers to come into extended use. The photograph shown below illustrates one of the latest forms of the silicon detector.

Fig. 162. Silicon Detector.

The large cup supported by the left-hand standard contacts several pieces of fused silicon embedded in fusible alloy. The right-hand standard supports a movable "offset" cup the same as that used on the Perikon type of Detector. A small piece of arsenic is mounted in this cup and may be brought to bear against any portion of any of the silicon crystals.

Pyron Detector.—The Pyron detector is not new, but the photograph shows a very simple and efficient form in which a fine wire is brought to bear against a crystal of iron pyrites mounted in a small cup.

Fig. 163. Pyron Detector.

Galena Detector.—Although galena is named in the list of sensitive minerals on page 132 it has come into such extensive use as a detector since the first edition of this book to be worthy of special attention. Galena detectors are often spoken of as "cat-whisker" detectors because of the long fine wire used to secure a delicate contact with the mineral.

The mineral is usually placed in a cup and held in position by imbedding in fusible alloy or clamped with a set screw. The best surface of the mineral should be selected by testing previous to imbedding it in the cup. Contact is made with the surface of the mineral by means of a piece of No. 30 phosphor bronze wire mounted on the end of a short brass rod fitted with an adjusting screw so that by turning or twisting the surface of the mineral may be "searched" and the tension varied.

Fig. 164. Galena Detector.

Such an arrangement is illustrated in Fig. 164. The base is a hard rubber block 3 3/4 x 1 3/4 x 1/2. The binding posts are of the type commonly used on electrical instruments. One of the posts is pivoted by placing a spring washer under the head of the screw which holds the post to the base. A short piece of brass rod fitted with a hard rubber knob passes through the wire hole in the post. A piece of No. 30 phosphor bronze wire is soldered to the end of the rod. By twisting the post and sliding the rod any portion of the mineral surface may be selected. Twisting the rod varies the tension of the contact.

The galena detector is connected in the receiving circuit in the same manner as other detectors of the mineral type.

THE AUDION.

The Audion—is finding favor in many amateur wireless stations, because of its almost entire lack of adjustment and of the loud clear signals which it gives even when used for long distance work.

The illustration shows the latest form of audion, the plate and the grid both being on the same side of the filament.

The filament of an audion is usually lighted by means of a six-volt storage battery. A small battery rheostat placed in series with the battery serves to regulate the amount of current flowing through the filament. Only one filament is used at a time, the other being saved as a reserve in case the first burns out.

Fig. 165. Audion.

The higher voltage necessary to operate an audion is supplied by a battery consisting of fifteen flashlight batteries, each flashlight battery being composed of three separate cells. The batteries are connected to an eight-point switch so that throwing the switch on the first point will connect five sets of batteries. The second point places five more in circuit and each additional point one set only. It is also a good plan to connect a four-point switch and three separate cells of battery in series with the eight-point switch so that they may be added to the circuit one at a time and the potential varied more closely than the steps on the eight-point switch permit. The maximum voltage of such a battery is approximately 56 volts.

The diagram in Fig. 166 shows exactly how an audion is connected. The wires A and B are the terminals leading to the tuning coil or loose coupler. It is not necessary that the telephone receivers used with an audion be wound to a high resistance in order to secure good results.

Fig. 166. Audion Circuit.

The audion is placed in operation by turning the rheostat until the filament lights brightly. Then adjust the voltage of the high potential battery until the signals are clearest. If the voltage is too high the audion will become filled with a bluish light and the voltage should be immediately reduced. The signals will be loudest when the filament is brilliantly lighted. No more current should be passed through the filament than is necessary to render the signals plain, for if "forced" its life will be limited to only a few hours.

Fig. 167. Rotary Variable Condenser.

APPENDIX.

[PUBLIC No. 264.]

[S. 6412.]

An Act to Regulate Radio Communication.

Be it enacted by the Senate and House of Representatives of the United States of America in Congress assembled. That a person, company, or corporation within the jurisdiction of the United States shall not use or operate any apparatus for radio communication as a means of commercial intercourse among the several States, or with foreign nations, or upon any vessel of the United States engaged in interstate or foreign commerce, or for the transmission of radiograms or signals the effect of which extends beyond the jurisdiction of the State or Territory in which the same are made, or where interference would be caused thereby with the receipt of messages or signals from beyond the jurisdiction of the said State or Territory, except under and in accordance with a license, revocable for cause, in that behalf granted by the Secretary of Commerce and Labor upon application therefor; but nothing in this Act shall be construed to apply to the transmission and exchange of radiograms or signals between points situated in the same State: Provided, That the effect thereof shall not extend beyond the jurisdiction of the said State or interfere with the reception of radiograms or signals from beyond said jurisdiction; and a license shall not be required for the transmission or exchange of radiograms or signals by or on behalf of the Government of the United States, but every Government station on land or sea shall have special call letters designated and published in the list of radio stations of the United States by the Department of Commerce and Labor. Any person, company, or corporation that shall use or operate any apparatus for radio communication in violation of this section, or knowingly aid or abet another person, company, or corporation in so doing, shall be deemed guilty of a misdemeanor, and on conviction thereof shall be punished by a fine not exceeding five hundred dollars, and the apparatus or device so unlawfully used and operated may be adjudged forfeited to the United States.

SEC. 2. That every such license shall be in such form as the Secretary of Commerce and Labor shall determine and shall contain the restrictions, pursuant to this Act, on and subject to which the license is granted; that every such license shall be issued only to citizens of the United States or Porto Rico or to a company incorporated under the laws of some State or Territory or of the United States or Porto Rico, and shall specify the ownership and location of the station in which said apparatus shall be used and other particulars for its identification and to enable its range to be estimated; shall state the purpose of the station, and, in case of a station in actual operation at the date of passage of this Act, shall contain the statement that satisfactory proof has been furnished that it was actually operating on the above-mentioned date; shall state the wave length or the wave lengths authorized for use by the station for the prevention of interference and the hours for which the station is licensed for work; and shall not be construed to authorize the use of any apparatus for radio communication in any other station than that specified. Every such license shall be subject to the regulations contained herein, and such regulations as may be established from time to time by authority of this Act or subsequent Acts and treaties of the United States. Every such license shall provide that the President of the United States in time of war or public peril or disaster may cause the closing of any station for radio communication and the removal therefrom of all radio apparatus, or may authorize the use or control of any such station or apparatus by any department of the Government, upon just compensation to the owners.

SEC. 3. That every such apparatus shall at all times while in use and operation as aforesaid be in charge or under the supervision of a person or persons licensed for that purpose by the Secretary of Commerce and Labor. Every person so licensed who in the operation of any radio apparatus shall fail to observe and obey regulations contained in or made pursuant to this Act or subsequent Acts or treaties of the United States, or any one of them, or who shall fail to enforce obedience thereto by an unlicensed person while serving under his supervision, in addition to the punishments and penalties herein prescribed, may suffer the suspension of the said license for a period to be fixed by the Secretary of Commerce and Labor not exceeding one year. It shall be unlawful to employ any unlicensed person or for any unlicensed person to serve in charge or in supervision of the use and operation of such apparatus, and any person violating this provision shall be guilty of a misdemeanor, and on conviction thereof shall be punished by a fine of not more than one hundred dollars or imprisonment for not more than two months, or both, in the discretion of the court, for each and every such offense: Provided, That in case of emergency the Secretary of Commerce and Labor may authorize a collector of customs to issue a temporary permit, in lieu of a license, to the operator on a vessel subject to the radio ship Act of June twenty-fourth, nineteen hundred and ten.

SEC. 4. That for the purpose of preventing or minimizing interference with communication between stations in which such apparatus is operated, to facilitate radio communication, and to further the prompt receipt of distress signals, said private and commercial stations shall be subject to the regulations of this section. These regulations shall be enforced by the Secretary of Commerce and Labor through the collectors of customs and other officers of the Government as other regulations herein provided for.

The Secretary of Commerce and Labor may, in his discretion, waive the provisions of any or all of these regulations when no interference of the character above mentioned can ensue.

The Secretary of Commerce and Labor may grant special temporary licenses to stations actually engaged in conducting experiments for the development of the science of radio communication, or the apparatus pertaining thereto, to carry on special tests, using any amount of power or any wave lengths, at such hours and under such conditions as will insure the least interference with the sending or receipt of commercial or Government radiograms, of distress signals and radiograms, or with the work of other stations.

In these regulations the naval and military stations shall be understood to be stations on land.

REGULATIONS.

NORMAL WAVE LENGTH.

First. Every station shall be required to designate certain definite wave length as the normal sending and receiving wave length of the station. This wave length shall not exceed six hundred meters or it shall exceed one thousand six hundred meters. Every coastal station open to general public service shall at all times be ready to receive messages of such wave lengths as are required by the Berlin convention. Every ship station, except as hereinafter provided, and every coast station open to general public service shall be prepared to use two sending wave lengths, one of three hundred meters and one of six hundred meters, as required by the international convention in force: Provided, That the Secretary of Commerce and Labor may, in his discretion, change the limit of wave length reservation made by regulations first and second to accord with any international agreement to which the United States is a party.

OTHER WAVE LENGTHS.

Second. In addition to the normal sending wave length all stations, except as provided hereinafter in these regulations, may use other sending wave lengths: Provided, That they do not exceed six hundred meters or that they do exceed one thousand six hundred meters: Provided further, That the character of the waves emitted conforms to the requirements of regulations third and fourth following.

USE OF A "PURE WAVE"

Third. At all stations if the sending apparatus, to be referred to hereinafter as the "transmitter," is of such a character that the energy is radiated in two or more wave lengths, more or less sharply defined, as indicated by a sensitive wave meter, the energy in no one of the lesser waves shall exceed ten per centum of that in the greatest.

USE OF A "SHARP WAVE."

Fourth. At all stations the logarithmic decrement per complete oscillation in the wave trains emitted by the transmitter shall not exceed two-tenths, except when sending distress signals or signals and messages relating thereto.

USE OF "STANDARD DISTRESS WAVE."

Fifth. Every station on shipboard shall be prepared to send distress calls on the normal wave length designated by the international convention in force, except on vessels of small tonnage unable to have plants insuring that wave length.

SIGNAL OF DISTRESS.

Sixth. The distress call used shall be the international signal of distress: dot dot dot, dash dash dash, dot dot dot.

USE OF "BROAD INTERFERING WAVE" FOR DISTRESS SIGNALS.

Seventh. When sending distress signals, the transmitter of a station on shipboard may be tuned in such a manner as to create a maximum of interference with a maximum of radiation.

DISTANCE REQUIREMENT FOR DISTRESS SIGNALS.

Eighth. Every station on shipboard, wherever practicable, shall be prepared to send distress signals of the character specified in regulations fifth and sixth with sufficient power to enable them to be received by day over sea a distance of one hundred nautical miles by a shipboard station equipped with apparatus for both sending and receiving equal in all essential particulars to that of the station first mentioned.

FOR DISTRESS SIGNALS.

Ninth. All stations are required to give absolute priority to signals and radiograms relating to ships in distress; to cease all sending on hearing a distress signal; and, except when engaged in answering or aiding the ship in distress, to refrain from sending until all signals and radiograms relating thereto are completed.

REDUCED POWER FOR SHIPS NEAR A GOVERNMENT STATION.

Tenth. No station on shipboard, when within fifteen nautical miles of a naval or military station, shall use a transformer input exceeding one kilowatt, nor, when within five nautical miles of such a station, a transformer input exceeding one-half kilowatt, except for sending signals of distress, or signals or radiograms relating thereto.

INTERCOMMUNICATION.

Eleventh. Each shore station open to general public service between the cost and vessels at sea shall be bound to exchange radiograms with any similar shore station and with any ship station without distinction of the radio systems adopted by such stations, respectively, and each station on shipboard shall be bound to exchange radiograms with any other station on shipboard without distinction of the radio systems adopted by each station respectively.

It shall be the duty of each such shore station, during the hours it is in operation, to listen in at intervals of not less than fifteen minutes and for a period not less than two minutes, with the receiver tuned to receive messages of three hundred meter wave lengths.

DIVISION OF TIME.

Twelfth. At important seaports and at all other places where naval or military and private or commercial shore stations operate in such close proximity that interference with the work of naval and military stations can not be avoided by the enforcement of the regulations contained in the foregoing regulations concerning wave lengths and character of signals emitted, such private or commercial shore stations as do interfere with the reception of signals by the naval and military stations concerned shall not use their transmitters during the first fifteen minutes of each hour, local standard time. The Secretary of Commerce and Labor may, on the recommendation of the department concerned, designate the station or stations which may be required to observe this division of time.

GOVERNMENT STATIONS TO OBSERVE DIVISION OF TIME.

Thirteenth. The naval or military stations for which the above mentioned division of time may be established shall transmit signals or radiograms only during the first fifteen minutes of each hour, local standard time, except in case of signals or radiograms relating to vessels in distress, as hereinbefore provided.

USE OF UNNECESSARY POWER.

Fourteenth. In all circumstances, except in case of signals or radiograms relating to vessels in distress, all stations shall use the minimum amount of energy necessary to carry out any communication desired.

GENERAL RESTRICTIONS ON PRIVATE STATIONS.

Fifteenth. No private or commercial station not engaged in the transaction of bona fide commercial business by radio communication or in experimentation in connection with the development and manufacture of radio apparatus for commercial purposes shall use a transmitting wave length exceeding two hundred meters, or a transformer input exceeding one kilowatt, except by special authority of the Secretary of Commerce and Labor contained in the license of the station: Provided, That the owner or operator of a station of the character mentioned in this regulation shall not be liable for a violation of the requirements of the third or fourth regulations to the penalties of one hundred dollars or twenty-five dollars, respectively, provided in this section unless the person maintaining or operating such station shall have been notified in writing that the said transmitter has been found, upon tests conducted by the Government, to be so adjusted as to violate the said third and fourth regulations, and opportunity has been given to said owner or operator to adjust said transmitter in conformity with said regulations.

SPECIAL RESTRICTIONS IN THE VICINITIES OF GOVERNMENT STATIONS.

Sixteenth. No station of the character mentioned in regulation fifteenth situated within five nautical miles of a naval or military station shall use a transmitting wave length exceeding two hundred meters or a transformer input exceeding one-half kilowatt.

SHIP STATIONS TO COMMUNICATE WITH NEAREST SHORE STATIONS.

Seventeenth. In general, the shipboard stations shall transmit their radiograms to the nearest shore station. A sender on board a vessel shall, however, have the right to designate the shore station through which he desires to have his radiograms transmitted. If this can not be done, the wishes of the sender are to be complied with only if the transmission can be effected without interfering with the service of other stations.

LIMITATIONS FOR FUTURE INSTALLATIONS IN VICINITIES OF GOVERNMENT STATIONS.

Eighteenth. No station on shore not in actual operation at the date of the passage of this Act shall be licensed for the transaction of commercial business by radio communication within fifteen nautical miles of the following naval or military stations, to wit: Arlington, Virginia; Key West, Florida; San Juan, Porto Rico; North Head and Tatoosh Island, Washington; San Diego, California; and those established or which may be established in Alaska and in the Canal Zone; and the head of the department having control of such Government stations shall, so far as is consistent with the transaction of governmental business, arrange for the transmission and receipt of commercial radiograms under the provisions of the Berlin convention of nineteen hundred and six and future international conventions or treaties to which the United States may be a party, at each of the stations above referred to, and shall fix the rates therefor, subject to control of such rates by Congress. At such stations and wherever and whenever shore stations open for general public business between the coast and vessels at sea under the provisions of the Berlin convention of nineteen hundred and six and future international conventions and treaties to which the United States may be a party shall not be so established as to insure a constant service day and night without interruption, and in all localities wherever or whenever such service shall not be maintained by a commercial shore station within one hundred nautical miles of a naval radio station, the Secretary of the Navy shall, so far as is consistent with the transaction of governmental business, open naval radio stations to the general public business described above, and shall fix rates for such service, subject to control of such rates by Congress. The receipts from such radiograms shall be covered into the Treasury as miscellaneous receipts.

SECRECY OF MESSAGES.

Nineteenth. No person or persons engaged in or having knowledge of the operation of any station or stations shall divulge or publish the contents of any messages transmitted or received by such station, except to the person or persons to whom the same may be directed, or their authorized agent, or to another station employed to forward such message to its destination, unless legally required so to do by the court of competent jurisdiction or other competent authority. Any person guilty of divulging or publishing any message, except as herein provided, shall, on conviction thereof, be punishable by a fine of not more than two hundred and fifty dollars or imprisonment for a period of not exceeding three months, or both fine and imprisonment, in the discretion of the court.

PENALTIES.

For violation of any of these regulations, subject to which a license under sections one and two of this Act may be issued, the owner of the apparatus shall be liable to a penalty of one hundred dollars, which may be reduced or remitted by the Secretary of Commerce and Labor, and for repeated violations of any of such regulations, the license may be revoked.

For violation of any of these regulations, except as provided in regulation nineteenth, subject to which a license under section three of this Act may be issued, the operator shall be subject to a penalty of twenty-five dollars, which may be reduced or remitted by the Secretary of Commerce and Labor, and for repeated violations of any such regulations, the license shall be suspended or revoked.

SEC. 5. That every license granted under the provisions of this Act for the operation or use of apparatus for radio communication shall prescribe that the operator thereof shall not wilfully or maliciously interfere with any other radio communication. Such interference shall be deemed a misdemeanor, and upon conviction thereof the owner or operator, or both, shall be punishable by a fine of not to exceed five hundred dollars or imprisonment for not to exceed one year, or both.

SEC. 6. That the expression "radio communication" as used in this Act means any system of electrical communication by telegraphy or telephony without the aid of any wire connecting the points from and at which the radiograms, signals, or other communications are sent or received.

SEC. 7. That a person, company, or corporation within the jurisdiction of the United States shall not knowingly utter or transmit, or cause to be uttered or transmitted, any false or fraudulent distress signal or call or false or fraudulent signal, call, or other radiogram of any kind. The penalty for so uttering or transmitting a false or fraudulent distress signal or call shall be a fine of not more than two thousand five hundred dollars or imprisonment for not more than five years, or both, in the discretion of the court, for each and every such offense, and the penalty for so uttering or transmitting, or causing to be uttered or transmitted, any other false or fraudulent signal, call, or other radiogram shall be a fine of not more than one thousand dollars or imprisonment for not more than two years, or both, in the discretion of the court, for each and every such offense.

SEC. 8. That a person, company, or corporation shall not use or operate any apparatus for radio communication on a foreign ship in territorial waters of the United States otherwise than in accordance with the provisions of sections four and seven of this Act and so much of section five as imposes a penalty for interference. Save as aforesaid, nothing in this Act shall apply to apparatus for radio communication on any foreign ship.

SEC. 9. That the trial of any offense under this Act shall be in the district in which it is committed, or if the offense is committed upon the high seas or out of the jurisdiction of any particular State or district the trial shall be in the district where the offender may be found or into which he shall be first brought.

SEC. 10. That this Act shall not apply to the Phillippine Islands.

SEC. 11. That this Act shall take effect and be in force on and after four months from its passage.

Approved, August 13, 1912.

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Illustrated. 8vo., cloth, 5 vols. The set $15.00. Each $3.50

Vol. I. Illustrated. 8vo., cloth, 90 pp $1.50

Illustrated. 8vo., cloth, 74 pp Net, $1.50

KINZBRUNNER, C. Continuous-Current Armatures; their Winding and Construction.

79 Illustrations. 8vo., cloth, 80 pp Net, $1.50

KLINGENBERG, G. Large Electric Power Stations.

Their design and construction, with examples of existing stations. 180 illustrations, 7 plates, 7 x 10, cloth, 260 pp Net, $5.00

A practical and theoretical treatise on the development, design, construction, equipment and operation of hydroelectric transmission plants. Second Edition. 500 illustrations. 4to., cloth, 475 pp. Net, $5.00

LANCASTER, M. Electric Cooking, Heating and Cleaning.

Edited by W. E. Lancaster, American Edition by S. L. Coles, 305 illustrations, 6 x 8 1/2, cloth 340 pp Net, $1.00

LARNER, E. T. The Principles of Alternating Currents for Students of Electrical Engineering. Illustrated with Diagrams. 12mo., cloth, 144 pp Net, $1.25

LEMSTROM, S. Electricity in Agriculture and Horticulture.

Illustrated. 8vo., cloth Net, $1.50

Being a practical treatise on the proper method of operating a street-railway motor-car; also giving details how to overcome certain defects. Second Edition. Illustrated. 16mo., cloth, 247 pp Net, $1.00

122 illustrations. 5 1/2 x 8 3/4, cloth, 228 pp Net, $3.50

LOCKWOOD, T. D. Electricity, Magnetism, and Electro-Telegraphy.

A Practical Guide and Handbook of General Information for Electrical Students, Operators, and Inspectors. Fourth Edition. Illustrated. 8vo., cloth, 374 pp $2.50

Being a description of the work of Hertz and his successors. Third Edition Illustrated. 8vo., cloth Net, $2.00

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MALCOLM, W. H. Theory of the Submarine Telegraph Cable.

In Press

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MASSIE, W. W., and UNDERBILL, C. R. Wireless Telegraphy and Telephony Popularly Explained.

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MIESSNER, B. F. Radiodynamics.

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Berlin, 1827. Translated by William Francis. With Preface and Notes by Thos. D. Lockwood. Second Edition. Illustrated. 16mo., cloth, 269 pp. (No. 102 Van Nostrand's Science Series.) 50 cents

(The Ward Leonard System.) 13 illustrations. 12mo., paper, 27 pp. (U. S. Navy Electrical Series No. 1.) Net, .50

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Electric Lighting. Translated from the French by G. W. Patterson, Jr., and M. R. Patterson. Second Edition. Fully Illustrated. 8vo., cloth, 324 pp $4.00

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Third Edition. With 140 full-page Plates, 65 Tables, and 165 pages of descriptive letter-press. 4vo., cloth, 300 pp. $7.50

PATCHELL W. H. Application of Electric Power to Mines and heavy Industries.

91 illustrations 6 1/2 x 9 1/4, cloth, 203 pp Net, 4.00

139 illustrations, 5 1/4 x 7 1/4. cloth, 203 pp Net, $2.00

PERRINE, F. A. C. Conductors for Electrical Distribution: Their Manufacture and Materials the Calculation of Circuits, Pole Line Construction, Underground Working, and other Uses.

Second Edition. Illustrated. 8vo., cloth, 287 pp Net, $3.50

A Handbook for Electricians and Operators. Seventeenth Edition. Illustrated. 8vo., cloth, 234 pp $1.50

Third Edition In Press

52 illustrations. 5 x 7, cloth, 187pp Net, $2.00

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85 illustrations. 4 1/2 x 6 3/4, cloth, 123 pp. (Installation Manuals Series) .50

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A series of laboratory experiments for first and second-year students in electrical engineering. Illustrated with many Diagrams. 8vo., cloth, 218 pp Net, $2.00

Printed on deckle edge Japan paper 400 pp. of text, 152 full-page plates. 8vo., cloth Net, $5.00

Translated from the German by James Erskine-Murray. Illustrated. 5vo., cloth, 224 pp Net, $3.50

71 Illustrations. 8vo., cloth, 275 pp Net, $3.00

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Second Edition, revised and enlarged. Illustrated. 8vo., cloth, 269 pp Net, $2.50

Second Edition, corrected. Illustrated . 8vo., cloth, 229 pp Net, $2.00

SEWELL, T The Construction of Dynamos (Alternating and Direct Current).

A Text-book for students, engineering contractors, and electricians-in-charge. Illustrated. 8vo., cloth, 316 pp $3.00

SHELDON, S., and HAUSMANN, E Dynamo-Electric Machinery: Its Construction, Design, and Operation.

Vol.1.: Direct-Current Machines.

Ninth Edition, completely re-written. Illustrated. 12mo., cloth, 281 pp Net, $2.50

Tenth Edition, rewritten. cloth, 353 pp Net, $2.50

SLOANE, T. O'CONOR. Elementary Electrical Calculations.

A Manual of Simple Engineering Mathematics, covering the whole field of Direct Current Calculations, the basis of Alternating Current Mathematics, Networks, and typical cases of Circuits, with Appendices on special subjects. 8vo., cloth. Illustrated. 304 pp Net, $2.00

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The Transmission and Distribution of Electric Power by Continuous and Alternating Currents. With a Section on the Applications of Electricity to Mining Work. Second Edition. Illustrated. 8vo., cloth, 411 pp Net, $4.00

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Edited, with Preface, by T. Commerford Martin. Folding Plate and Numerous Illustrations. 16mo., cloth, 241 pp. (No. 109 Van Nostrand's Science Series.) 50 cents

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With an Introduction and Notes by Frank L. Pope and H. R. Butler. Illustrated 16vo., cloth, 214 pp. (No. 66 Van Nostrand's Science Series.) 50 cents

TOWNSEND, FITZHUGH. Alternating Current Engineering.

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VOSMAER, A. Ozone. Its Manufacture and Uses.

76 illustrations. 6 x 9, cloth, 210 pp Net, $2.50

Second Edition, corrected 265 illustrations. 8vo., cloth, 501 pp. Net, $4.00

A simple practical pocket guide on the construction, operation, maintenance, and testing of primary batteries for automobile, motorboat, and stationary engine ignition service. 26 illustrations. 5 x 7, cloth, 79 pp Net, 0.50

Third Edition. Illustrated. 16mo., cloth, 104 pp. (No. 68 Van Nostrand's Science Series.) 50 cents.

WATT, ALEXANDER. Electroplating and Refining of Metals

New Edition, rewritten by Arnold Philip. Illustrated 8vo., cloth, 704 pp Net, $4.50

WEBB, H. L. A Practical Guide to the Testing of Insulated Wires and Cables

Sixth Edition. Illustrated. 12mo., cloth., 118pp $1.00

Second Edition, completely revised. 313 illustrations. 8vo., cloth, 580 pp Net, $6.00

300 illustrations. 6 x 9, cloth, 355 pp Net, $2.50

19 Illustrations. 16mo., cloth, 88 pp. (Installation Serious Manuals.) Net, 50 cents.

Illustrated. 8vo., cloth, 264 pp Net, $4.00

160 Illustrations. 8vo., cloth, 188 pp Net, $2.00

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