east of the tunnel house.

At intervals of about five built in the Edison tube

hundred feet, manholes are portion, as well as in the conduit portion, of the trunk line, thus affording a quick means of locating low-insulation points as they develop. Each of the tubes and cables is provided with an amperemeter at

station No. 1, and with switches at both ends, so that they may be completely disconnected from the system in case of trouble. Two of the 3,000,000circular-mils tubes are provided with throwover switches and arranged so that they may be quickly connected either to the positive or neutral or negative

or neutral at will.

All of the cables are provided with throwover switches on both ends, so that they may be operated either as positive or negative at will, thus providing for any possible contingency that may arise. At the Adams street sub-station the trunk line feeds into the main 'bus-bar in the distribution room, and from the switchboard forty-two feeders radiate to various points in the business district, ranging in size from 250,000 circular mils to 1,000,000 circular mils, and in length from 290 feet to 2,831 feet, the average size being 485,000 circular mils, and the average length of feeder 1,373 feet.

The maximum current in amperes carried over the trunk line and distributed from the Adams street sub-station last December was 34,400 amperes, the maximum loss of pressure on the trunk line being 12.4 per cent, and to the customers' meter 22.8 per cent, the distance to farthest feeder end being 6,171 feet. In addition to the current furnished to the trunk line, station No. I also delivers from its main 'bus-bar current to the two 1,000,000-circular-mil feeders that feed into two points in the southern portion of the business district. One of these feeders, terminating at Wabash avenue and Harrison street, is 3,800 feet in length, and carries, with maximum station. pressure, 780 amperes on each side; the other, terminating at Eldredge court and State street, is 4,800 feet in length, and carries, with maximum station pressure, 620 amperes on each side. The supplying of district No. 1 by station No. 5 is done in much the same manner as that just described by the two feeders from station No. 1 into the southern portion of the district. From station No. 5 eight feeders, varying in size from 400,000 circular mils to 1,000,000

circular mils, and in length from 2,175 feet to 4,445 feet, terminating at different points in the northern section of district No. 1, deliver a total of 7,600 amperes at maximum station pressure of 140 volts, the amount of current furnished during the run being only enough to maintain standard system pressure at the feeder ends, the curve of station voltage following very closely that of station No. 1.

Station No. 2, which is now really a rotary-transformer sub-station, is 17,500 feet from station No. 1, and 14,300 feet from Adams street sub-station. The load diagram "B" shows the amperes delivered to district No. 2, the cross-hatched portion representing the current furnished through the rotary transformers and the unshaded portion representing the current furnished by the dynamos in station No. 2, the dynamos and rotary transformers operating in parallel on the three-wire system. The upper curve shows the total amperes delivered to district No. 2.

Station No. 4, which now operates only from dusk till midnight, and will later become a sub-station, is 11,500 feet from station No. 1, 9,000 feet from station No. 5, and 8,000 feet from Adams street substation. The load diagram "C" shows the amperes delivered to district No. 4. The portion of the curve from midnight until 3.30 p. m. on the winter day and until 6.30 p. m. on the summer day is furnished from district No. 1 through the inter-connected underground network, the district No. 4 being, during these hours, merely an extension of district No. 1, and having no distinct supply delivered through its own switchboard. From dusk till midnight the generating plant in station No. 4 is operated, and the current is delivered as shown by the next to the highest curve on the diagram, the low curve marked No. 5 representing

the amperes furnished by station No. 5 to district No. 4 over a direct-current tie line between the

switchboards of the two stations. The tie line is made up from one feeder running out of station. No. 5, originally feeding into district No. 1 and now connecting, by means of river cables, with a feeder

out of station No. 4, which formerly fed into the district at a southern point.

This tie line is also used pressure in district No. 4

on dark days to keep up the by connecting onto the main 'bus in station No. 5 and allowing it to take a small current and deliver it to station No. 4 switchboard, thus relieving the network

between districts No. 1 and No. 4 of some of the work. Between the hours of midnight and eight o'clock in the morning there is only one low-tension, direct-current generating station operating (station No. 1), supplying direct current to district No. 1, and through the network to district No. 4.

District No. 2 is supplied from station No. 1 by means of a converse rotary transformer connected to the 250-volt direct-current 'bus-bars, converting to three-phase alternating current at about 160 volts. By means of step-up transformers, this is raised to 4,500 volts and at this pressure the energy is transmitted by three-phase underground transmission line to station No. 2, where it is reduced by step-down transformers to about eighty volts and converted by means of rotary-current transformers to direct current at about 115 volts.

For the permanent conversion of station No. 2 into a sub-station, a pair of special pair of special 200-kilowatt generators are being installed, directly coupled to the existing 600-horse-power, triple-expansion engines in station No. I. Each generator is provided with a commutator and a set of three collector rings, and is designed to deliver from the same armature direct currents and three-phase alternating currents; the directcurrent sides of each pair of machines being connected in series to form a three-wire unit, and the alternatingcurrent sides, after passing through transformers stepping up to 4,500 volts, being connected in multiple. The alternating current from these machines. will be taken to supply the transmission line to station No. 2, and the balance of the capacity of the machines will be delivered directly into the main direct-current 'bus-bar of station No. 1, thus keeping the unit operating at full load and maximum efficiency