SCIENTIFIC AMERICAN SUPPLEMENT, No. 525. 8387 rounded by a mass of lead (Fig. 2) . Moreover, to each of the light conductors there is soldered a conductor one-third of an inch in diameter t,hat communicates through a metallic contact embedded in a block of retort carbon, 3}4 ft. long by 2 wide. All these contacts together present a surface of more than twenty-four square yards. J'Tll . S The pipe that leads the conductors to the water and gas mains is a semi-cylinder of cast iron provided with

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... cover. The conductors are placed in this, and the E ipe i §... .filled with coal-tar pitch to prevent rusting ( Fig. 51. Fig. 4 shows the mode of communication of the conductors with the system of gas pipes. To the gas pipe, after its surface had been wel cleaned, was soldered, by means of tin, a sheet of copper one-third I)f an inch thick and 1� inch long, in which are ad· justed 16 brass screws with strong heads containing an aperture for the passage of the conductors. Each of these latter, then, communicates with two screws. The whole is well tinned, and then wound with cloth over which gas tal' has been spread. Finally, there is a masonry chamber into which an entrance may be effected through a manhole, inorder that the state of the contact may be inspected. Fm. 4. The-junction of the conductors with the water main was made as follows (Fig. 6) : For want of enough galvanized iron wire � in. in diameter, it became necessary to use wire about half that size. So, in order to obtain perceptibly the same total section for each of the three series, it became Ilecessary to employ twenty wires instead of eight in order to carry out this idea. The three series of subterranean conductors, then, ning rod. The water main used is 20 inches in diame ter and � inch in thickness.