Page:Popular Science Monthly Volume 88.djvu/405

 Populor Science Monihly

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��quarter revolution the distributors con- nect on the Hne four operators using one duplex "channel" set, which consists of a sender and receiver at each end.

The operation of the two distributors is perhaps the most important new thing in this system, since it is through them that the line can be used successively by each of the four groups of four oper- ators. The simple fact that in printing telegraphs over three-cjuarters of the to- tal time of operation is used for prepar- ing to send, and in printing the letters,

��plished in one-tifth of a second, and dur- ing each quarter of this period, or one- twentieth of a second, each set of in- struments is connected to the line. In the three-twentieths of a second the re- ceiving printer operates and the trans- mitter prepares to send the set of five impulses corresponding to the next letter in its message.

The other photograph shows the eight operators, four sending and four receiv- ing, who work at one end of a trunk line using this new c[uadruple-duplex printer.

���The problem of bridging a mountain stream, circling the edge of a precipice and "tacking" up a steep grade forced the engineers responsible for the electric railway up Mt. Lowe to

make this queer "circular bridge"

��while less than one-quarter will suffice for the actual transmission of the five electrical impulses, has made possible this distribution and simultaneous op- eration. The distributors are merely special rotary switches which revolve, one at each end of the wire, at exactly the same efifectixe speed. For each quarter revolution the duplex line is con- nected to one set of instruments and the impulses forming one letter are transmitted in both directions. If the distributor rotates at three hundred rev- olutions per minute, three hundred let- ters or fifty words per minute will be sent in each direction through each of the four channels, making a total of four hundred words per minute. Each revolution of the distributor is accom-

��A Circular Bridge on Stilts

THE circular bridge shown in the il- lustration is unusual both in its de- sign and in its location. The trestle work forming almost a complete circle, practically all of which is "on stilts," is a part of a mountain inclined road. At the point where the roads almost meet, one track is about six feet higher than the other. The circle formed by this track is seventy feet in diameter.

This bridge is also noteworthy be- cause it is located nearly five thousand feet above sea level. It is a portion of what is known as "The Mt. Lowe in- cline railway," a line which winds its way up the side of Mt. Lowe. The turn seems to show how crooked is this three- mile line.

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