EXTRACTS FROM LETTERS OF MR. HOLLIS FRENCH TO GEORGE G. SHEDD, RELATIVE TO DIRECT CURRENT TRANSMISSION.

With regard to the plan of electrical transmission of power proposed by Lord Kelvin in this case, one recognizes with difficulty, from the description in the newspaper article submitted, any known system. From Lord Kelvin's attitude in other matters, however, there is reason to believe that he refers to the socalled direct or continuous constant current system of transmission as distinguished from that making use of alternating current at constant potential.

Ignoring the reporter's incoherent description of the plan, it may be said that the direct current system has been discussed considerably in Europe where lis most ardent advocate is M. Rene Thury, chief engineer of the Campagnie ae L'Industrie Electrique et Mecanique of Geneva. Largely through his efforts at least two plants have been installed on the Continent where this system has been adopted.

One of these plants supplies the town of Lausarne, Switzerland, with direct current transmitting about 5,000 h. p. from St. Maurice, a distance of 35 miles, at 23,000 v. potential.

The other plant transmits several thousand horse power at 60,000 v. from Montiers to Lyons, France, a distance of 110 miles.

This plan has also been considered for the great Victoria Falls project where from 150,000 v. to 200,000 v. have been figured on. At the present time, however, it is believed that the Lyons project above referred to is the largest and most important transmission of this kind ever attempted, though some interesting experiments were carried on at Geneva a few years ago, using direct current at seventy thousand volts potential.

It cannot be said that the majority of engineers, particularly in this country, consider this scheme very seriously, but it must be admitted that it has made sufficient headway in Europe to be entitled to a good deal of thought.

Briefly described, it is a system using direct current at a constant strength with a varying potential, just as is used on the direct current arc system in operation in this country though on a different scale. It is, therefore, quite the reverse of the constant potential system where the current varies with the road.

For fong distance transmission of any size it means that a large number of generating units must be used, connected in series. Each dynamo generates a constant current at a certain voltage. Two will, therefore, generate the same current, and when connected in series will double the voltage. Three will give thrice the voltage, and so on, the current remaining at constant strength.

The line voltage is thus raised by the necessary addition of generating units to a point as high as is desired for the tranmission.

This plan possesses the great disadvantage of requiring a large number of generating units, which is thus quite the reverse of modern practice of using as few units as possible. It also has the objection of requiring a similar number of units at the receiving end of the line to step down to working voltages. All of these machines, being constant current dynamos, are of course provided with commutators, which are entirely done away with at great advantage in the alternating current system. Altogether the number of machines with this system is greatly in excess of those that would be provided with an alternating current plant, which means that floor space and attendance are at a maximum with continuous current. These machines, moreover, have to be thoroughly insulated from the ground, requiring very careful construction.

On the other hand, the switchboard arrangements are very simple indeed and the use of direct current on the line considerably lessens the problem of insulation and strain on the insulators, which requires such careful consideration in alternating current lines.

As for the question of copper, the inevitable loss in conductors has to be faced whether constant current or constant potential is adopted, because no

amount of figuring can escape Ohm's law. At equal maximum voltage for a given amount of energy transmitted, the full load current on the line is the same whether we work at constant potential or constant current. The difference is that at constant current the energy loss is constant at all loads, while at constant potential the insulation strain is constant.

The relative importance of these two conditions at high voltage remains to be determined.

It may safely be said that for the project under discussion, there is no question but that a proper alternating current system of transmission can easily be worked out along the lines of standard practice in this country, and it may very easily be doubted if a direct current system would offer any advantage in this case, either from point of view of operation or of first cost, especially when it is remembered that the machinery and devices required would have to be imported from abroad for the purpose.

(Signed) HOLLIS FRENCH.

APPENDIX C.

REPORT UPON VALUE OF BUILDINGS INCLUDED WITHIN THE LIMITS OF THE PROPOSED GENESEE RIVER STORAGE RESERVOIR IN TOWNS OF GENESEE FALLS, PORTAGE, GRANGER, HUME, AND CANEADEA.

MR. JOHN R. FREEMAN, Consulting Engineer, Providence, R. I.: DEAR SIR. Responding to your request to present a brief report upon the value of all buildings within the limits of the proposed Genesee storage reservoir at Portage, N. Y., I respectfully submit the following outline and results of my estimate.

Each house or building in the five towns of Genesee Falls, Portage, Granger, Hume and Caneadea, within the limits of the proposed reservoir, was visited between December 10th and 23d, inclusive, 1907, and approximate dimensions of all buildings noted, together with my judgment of the value per cubic foot, guided by a carefully prepared and checked schedule of unit values for varying types of buildings.

The values of the buildings thus obtained were checked in as many instances as possible by means of the assessed valuation, or otherwise, as opportunity offered. The information thus obtained is summarized for the five towns in table attached.

It will be noted that, including the village of Houghton, which may not be disturbed, there are 1,096 buildings in all, classified as follows:

349 dwellings.

630 minor buildings connected therewith.

8 churches.

9 schoolhouses.

30 stores.

70 other buildings.

These "other buildings are principally small shops, quarry sheds, cheese factories, saw mills, hotels, etc. There are no large manufacturing concerns in the valley, the largest being the new plant of the L. C. Roberts Mfg. Co. at Fillmore, where they are just starting in to manufacture concrete machinery.

There are two quarries which would be flooded out: The Portageville Bluestone Co., which is said to do business of about $40,000 to $50,000 a year (gross value of stone shipped) and the Genesee Valley Bluestone Co., now shut down and in the hands of a receiver.

The estimated present market value of all buildings in the five towns is $515,626. Adding 50 per cent. to this value for the extra cost due to condemnation proceedings and other legal expenses, brings the total amount required to purchase this property for reservoir purposes to $773,439.

It will be noticed that this value of the buildings alone is in excess of Mr. George W. Rafter's estimate, in 1896, of the total land damages for this reservoir, which presumably included all buildings. When we add the value of land to be acquired it will be found that my estimate is more than 100 per cent. in excess of Mr. Rafter's figures, but, even with this marked discrepancy, I believe that my figures are conservative and are no more than should be estimated upon to cover all contingencies.

The full details of estimate will be found on sheets Nos. 1-67, inclusive, attached to full report, dated January 23, 1908. Very respectfully submitted,

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GEORGE G. SHEDD.