Boats run regularly from the dock at San Francisco over to the end of a very long mole, where is located the large depot. This mole is one of the longest in the world, the distance from the mainland to the depot being 17,160 feet, or 34 miles. The water of San Francisco Bay along the line of the mole averages 20 to 30 feet in depth, according to the tides; and the construction of the long track-way was a very expensive undertaking.

None of the ordinary poles and trolley wheels are used on the railway. What is known as the "Brown roller trolley," the invention of Mr. J. Q. Brown, General Engineer of the line, has been adopted. A roller two feet long is attached to the top of a diamond-shaped iron device. By means of strong steel springs, the roller is pushed up and kept in constant contact with the overhead current wire. The device is so constructed as to allow a vertical play of six feet in order to conform to variations of grade.

With the roller trolley there is no "jumping the wires," as with the ordinary narrow-grooved wheel. This cannot occur unless the car itself leaves the track. The roller is of great advantage also in running around curves; for, even at high speed, it cannot possibly "skip" from the wire. It simplifies greatly the overhead construction, doing away with all trolley frogs and

switches except at rightangle crossings, where a simple special design is employed.

The wear on the trolley wire, also, is smaller than with the wheel. The roller soon wears smooth and bright, and does not become corrugated and pitted. The device is practically noiseless, for the roller is packed with nonresonant matter that almost entirely destroys the vibration. There is but very little jar even when moving at a high rate of speed, while the train runs very smoothly and steadily. The roller exerts an upward pressure of only 24 pounds against the trolley wire. To operate a train of eight cars moving at a speed of 50 miles per hour, requires from 2,500 to 3,000 amperes to be collected from the overhead conductor.

A Sledge Locomotive IN the Maine lumber districts a very

curious motor is utilized to haul logs through the woods in winter time. It is what might be called a "sledge locomotive," for, in place of the ordinary wheels, the front part is mounted on runners as well as the rear. Under the heaviest part of the motor, however, is placed a wheel

LOG-HAULING TRACTION ENGINE.

machine will haul two or three car-loads of logs along a fairly level road through the woods, at the rate of from four to six miles an hour. It is brought into use after the snow has fallen sufficiently to form a fairly smooth surface for the runners, and it will ascend quite a steep grade.

Compressed Air in

Bridge Repairing

on the Illinois Central, on both new and repair work. The machines are generally placed in care of the superintendent; and after they are started, little or no attention is necessary, except the filling of the oil-cups. The arrangement of the compressor is automatic and is under the control of the engine's governor, thus making it economical, both in the use of fuel and in effecting a great saving in attendance.

recently performed on the Illinois Central Railroad, shows the high state of efficiency that compressed-air machinery has attained, and the important new fields that it is invading. By the aid of a portable gasoline air-compressor, field riveting was done on a railroad bridge without in any way hindering traffic over the structure. The compressor was set outside the rail a sufficient distance to permit the passing of trains. An entirely new floor system was riveted in position in this particular bridge, without interfering with the passage of trains. The

Electricity

created by the increased cost of operation. of steam railroads and the increasing competition of electric roads. It has equipped 40 miles of the busiest portion of its line with electricity, using the third rail,

ENGLISH ELECTRIC RAILROAD TRAIN.

and has thus become a pioneer in the substitution of electrical for steam motive power.

It would be difficult to find a road where the conditions were more unfavorable for the success of electrical operation than on the Northeastern, but the promoters have already proclaimed the experiment an absolute success. Traffic over the forty miles is exceedingly heavy; there are four tracks nearly all the distance; and crossings and other obstacles are numerous. The electric trains that have been installed consist of two motor coaches, with one trailer coach between them. They are operated by a continuous current obtained from a single collector placed in the six-foot way, with a return circuit through the running rails. The collector rail weighs eighty pounds to the yard, and is placed 3 feet 111⁄2 inches from the center of the track, and, where necessary, is protected by two creosoted boards bolted against distance pieces on each side of the rail. Under the protected rights of way of English roads, a third rail needs little protection, which is extremely different from the condition presented by American roads.

The electric rolling stock consists of motor and trailer coaches of the opencorridor type, lighted and heated by electricity. Each motor car is equipped with two motors, each of 150 horse-power. The motors used in the freight service are capable of hauling a train of 150 tons up a grade of 1 in 27 at a speed of between nine and ten miles per hour. For the

present the accommodation trains between Newcastle and Tynemouth will run at an average speed of about 22 miles an hour, including stops; and the express trains, at about 30 miles an hour.

YSTEMATIC arrangement of circuits, avoiding all confusion such as often results in the wiring of large office buildings, is the result of a new type of panel - board installed in the great Railway Exchange Building in Chicago, Illinois. The panelboard is compact, and at the same time

gives great flexibility in connecting the various circuits in the building to the metering system.

The general arrangement and connections of the device are shown in the accompanying, illustrations. The board is mounted on a shallow steel box and is divided into two sections, vertically (Fig. 1).

At the top the feeders from the three-wire service enter, and are led through the fuses to the main switch. The neutral passes from the switch down to two bus bars in the lower portion of the board. These bus bars are common

Fig. 2. In the latter figure, one of the meters is shown as registering on the two right-hand circuits at the top and bottom of the panel. When the lower one of these offices is to be vacated and the other retained, the meter can readily be changed to the one circuit by merely removing the jumper wire connecting the two, thus disturbing no other wiring.

The wiring of all the meters served by each panel-board is brought in at the sides near the top (Fig. 1), and the lamp circuits lead out opposite their respective switches at the lower portion of the board. The wiring on both sides is identical, although Fig. 1 shows it as entering one side.

Unscrewing two marble slabs at the rear, covering the fuses and wiring, gives access to the panel itself. Two small doors at the top and bottom of the case near the edge (Fig. 1) can be opened, to show at a glance which leads are connected to the respective fuses.

World's Largest Stone Arch

SO rapid is the progress made these

days in almost every line, that already the record of the noted Luxembourg bridge, completed in 1903 (See THE TECHNICAL WORLD, November, 1904, p. 311), has been beaten by a single-span