They were installed by a company that was acquired by purchase by the one first mentioned. As this company had long since adopted alternating current for its entire distribution, it was extremely desirable to be able to operate these city lamps from its large direct-connected alternators, thereby saving in fuel, attendance, floor space and reserve investment.

After a few months' trial of an experimental circuit with alternating current, it was found perfectly feasible to operate the same direct-current lamps, slightly remodeled, on the same circuits of sixty or eighty lamps in series. A system of this kind was, therefore, adopted and the company now has 2,300 of these lamps in regular operation by alternating current in this way. The circuits are each provided at the station with a regular step-up transformer of a maximum capacity of 4,000 volts and ten amperes, and the feeders to these transformers are treated on the switchboard in the same way as the feeders for incandescent lighting. It is quite usual for one generator to carry 2,000 of these lamps. The lighting is satisfactory to the city and the lamps give better service than when operated by direct current. There has been a very marked saving in fuel and attendance. The indicated horse-power per arc lamp is considerably less than with the direct-current arc lamps operated in the usual manner. Figure 4 shows this system in diagram.

I know of no other place where this is being done, and it stands as a very pronounced example of the flexibility and adaptability of alternating currents.

There have been a great many problems in the operation of large alternating-current stations that have been discouragingly difficult of solution. The handling of high potentials on switchboards, the operation of generators in multiple, with facility, and

scores of more or less important difficulties, have, one by one, been surmounted, the burden of the work usually falling on a few of the pioneer stations.

FIG. 4. A.G. SERIES ARC-LIGHT SYSTEM.

In summing up, we find the following marked features in which the alternating current, properly

installed, has been shown to have pronounced superiority over the direct current:

Highest possible efficiency of distribution and operation.

Best regulation.

Largest territory desired readily supplied from one station.

Comparatively small cost of feeders, effecting enormous saving in investment.

Least cost of real estate.

Cost of installing and operating sub-stations entirely voided.

The only system in which all classes of service can be supplied from one type of generator.

Greatest flexibility.

In closing, I wish to thank my friends and co-laborers of the direct-current faith, from several of whom I have had the pleasure of learning much that has proved of great value to me.

THE PRESIDENT: I will ask Mr. Ferguson to read his paper on general distribution from central stations by direct currents.

Mr. Ferguson read his paper, as follows:

GENERAL DISTRIBUTION FROM CENTRAL

STATIONS BY DIRECT CURRENTS

Mr. President and Gentlemen of the National Electric Light Association:

The subject of central-station distribution by direct currents is one that is so familiar to many of you that I hesitated when asked to write this paper, feeling that it would be difficult to present to you any new thoughts or experiences, so I trust you will pardon me if in the attempt to precipitate discussion and bring to the attention of the meeting the ideas and experiences of others, which is, after all, the object of my paper, I may trespass upon ground previously explored.

Nor do I wish to be construed as advocating blindly the general use of direct currents under all conditions for both transmission and distribution of electricity for lighting and power purposes in cities and towns, for records will, I think, clearly show that the writer was the first of the so-called Edison central-station men (who have represented the direct-current idea in central-station lighting) to advocate the introduction of the alternating current as a means of effecting important economies in the operating of the direct-current distribution systems, and also vastly extending their field of operation, which, without the combination of alternating currents, might have remained, despite their distinct advantages, unfortunately limited to a comparatively small and closely-populated area.

The general design of the modern direct-current

central station and its equipment has been fairly well established within the past five years, and while it was originally the custom to erect the generating stations as nearly as possible in the electrical centre of the city or town, it is now generally conceded that direct current may be more economically distributed from a condensing station situated even a mile distant from the electrical centre than from a non-condensing station located at the electrical centre of the city; and it has been further demonstrated that the former practice of building many central generating stations in various centres of distribution in cities is to be supplanted by the use of one or two large condensing stations, generating direct current for distribution throughout the business district if the station be within one mile of the electrical centre of the district, and alternating current for transmission to sub-stations located at the electrical centres of districts

remote from the main generating station. In some cities, water for condensing purposes may not be easily obtainable within a distance of one mile, and the location is then merely a question of total cost of land, building, and transmission lines to the various distributing stations; proper consideration being given, of course, to the limitations of line voltage and insulation.

In order to show the workings of the first-mentioned type of modern direct-current central-station systems, I will explain in a general way the method. of distribution employed in the system of the Chicago Edison company, which I think fairly represents the latest development in direct-current distribution, and will leave the explanations of the methods of directcurrent distribution in other cities to the representatives of the companies operating them.