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resistance low enough to relieve the line, before the arc can extinguish, the synchronous apparatus has been thrown out of step and the line shut down. The line, however, can at once be put into service again, which would not be the case if the insulation had punctured. The place for horns, then, is along the pole line at short intervals, as described before, and the gaps should be set for very high-voltage arc-over.
For constant-current arc-lamp circuits, horns form an excellent arrester, as only a small current is required to relieve the line, and resistance can be used. For mercury-arc rectifier arclamp circuits, this arrester is especially well adapted, as the multigap arrester will not operate on direct current.
LIQUID ELECTRODE ARRESTER
CHOKE COILS Choke coils should be used in conjunction with lightning arresters in all cases where the arrester protects station apparatus, except, 'however, on cable systems. The inductance of the coils must not be high, or they become a source of danger rather than protection. It is very important to have as low capacity as possible between turns, as with appreciable capacity high frequency, such as the coil is supposed to protect against, passes easily through from turn to turn.
REPORTS It is, of course, our common hope that in the near future lines may be run for longer distances at very much higher voltages than to-day. To accomplish this, much will depend upon the development of protective apparatus and a better understanding of the phenomena involved. For the common good, the designer of protective apparatus should be given every opportunity to study cause and effect, and it is not enough that he be told in a general way whether the operation of a line is satisfactory or not. He should receive regular definite reports, and observations should be carefully and scientifically made. Almost every line requires a certain amount of adjustment and experimenting after installation, and a careful record of disturbances should be kept in any case. Of course, there is a certain amount of trouble involved in keeping such a record, but it is decidedly worth the while. The writer is prepared to co-operate with any line wishing to keep such a record, and, if necessary, will supply instructions, record blanks and special fireproof test papers.
The new graded-resistance multigap arrester is especially suited to the study of lightning disturbances, for, as explained above, the various discharges of different nature take place by different paths through the resistances and gaps. It is hoped that, at least where these arresters are installed, the station men may be induced to become interested in the study of lightning.
The meeting then adjourned until Wednesday morning.
ORDER OF BUSINESS
WEDNESDAY, June 5, 1907
THIRD SESSION, 10 A. M.
Paper-New Developments in Arc Lamps and High-Effi
ciency Electrodes. By G. M. LITTLE Paper-Indefinite Candle-Power in Municipal Contracts.
By E. LEAVENWORTH ELLIOTT 3 Announcement-National Bureau of Standards. DR. S. W.
STRATTON 4 Paper-Indefinite Obligations in Municipal Contracts. By
HENRY FLOY 5 Report-Committee to Consider Specifications for Street
Lighting. DUDLEY FARRAND, Chairman 6 Report-Committee on Protection from Lightning and Other
Static Disturbances. Alex Dow, Chairman 7 Paper-Electric Heating Without Special Concessions from
the Central Station. By C. D. WOOD, JR.
FOURTH SESSION, 8 P. M.
I Paper-Efficiency of Various Methods of Illumination. By
E. A. NORMAN 2 Paper-The Frequencies of Flicker at Which Variations in
Illumination Vanish. By A. E. KENNELLY and S. E.
WHITING 3 Paper-Application of Gas Power to Gentral-Station Work.
By J. R. BIBBINS 4 Paper-The Future of the Gas Engine. By Lewis Nixon 5 Address—Lightning and Lightning Protection. By C. P.
STEINMETZ 6 Executive Session
President Williams called the meeting to order at ten o'clock Wednesday morning, and announced the first order of business to be the paper by Mr. G. M. Little, of Pittsburgh, entitled New Developments in Arc Lamps and High-Efficiency Electrodes.
Mr. Little presented the paper, as follows: NEW DEVELOPMENTS IN ARC LAMPS AND
Arcs for lighting may be formed between electrodes of many different kinds. This paper deals with the development of the so-called magnetite electrodes and of a lamp suitable for burriing them. A few points of comparison between these metallicoxide electrodes and carbon electrodes will be considered, and some of the many interesting advantages possessed by the metallic-oxide electrodes and lamp will be touched on. Among these are the long life, high efficiency and good distribution and color of light.
The magnetite electrodes were so named because magnetite is usually one of the constituents of the negative or cathode, but it would be more satisfactory to call them metallic-oxide elec
rodes, as in addition to the magnetite there are always at least two other oxides present, namely, oxide of titanium and oxide of chromium.
These electrodes are made in a very different manner from the carbon electrodes. As is well known, the latter are squirted or molded from a plastic mixture and are baked; the carbon furnishing sufficient mechanical strength and electrical conductivity. A metallic-oxide electrode can not be made this way, for it is a familiar fact that a fine powder is a poor conductor, no matter of what it is composed, and as these electrodes are made for the most part from finely powdered oxides, it is evident that a conducting binder or a conducting case would have to be used. In practice, the mixture of oxides is tamped into a thin iron tube and the end sealed in an arc.
The oxides have distinct and separate reasons for their presence. The titanium oxide has the property of rendering the arc luminous; and it may be here noted that the metallic-oxide arc is a flame arc, the light not coming from a crater as with carbons. The oxide of iron gives conductivity to the fused mixture when cold, the other oxides being conductors only when hot. The oxide of chromium prevents a too-rapid consumption, so that by its use an electrode may be given a very long life.