Probably the most important of the inventions relating to submarine telegraphs is the siphon recorder, invented by Sir William Thompson, now Lord Kelvin (U. S. Pat. No. 156,897, Nov. 17, 1874). It is called a siphon recorder because the record is made by a little glass siphon down which a flow of ink is maintained like a fountain pen. This siphon is vibrated by the electric impulses to produce on the paper strip a zigzag line, whose varying contour is made to represent letters. In the illustration, Fig. 15, _m_ is an ink well, _o_ a strip of paper, and _n_ the ink siphon, one end of which is bent and dips down into the ink well, and the other end of which traces the record on the moving paper strip _o_. The siphon is sustained on a vertical axis _l_, and its lateral vibration is effected as follows: A light rectangular coil _b b_, of exceedingly fine insulated wire, is suspended between the poles N S of a powerful electro-magnet energized by a local battery. In the coil _b b_ is a stationary soft iron core _a_, magnetized by the poles N S. The coil _b b_ is suspended upon a vertical axis consisting of a fine wire _f f_, and the delicate electrical impulses over the submarine cable enter the coil _b b_ through the axial wire _f f_ as a conductor, and cause a greater or less oscillation of the coil _b b_ between the poles N S of the electro-magnet. The coil _b b_ is connected by a thread _k_ to the siphon, and pulls the siphon in one direction, while the siphon is pulled in the opposite direction by a helical spring attached to an arm on the siphon axis _l_. The jagged lines seen in Fig. 16 spell the words “siphon recorder.” [Illustration: FIG. 15.--SIPHON RECORDER.] [Illustration: FIG. 16.--SIPHON RECORDER MESSAGE.] To-day there lie in submerged silence, but pulsating with the life of the world, no less than 1,500 submarine telegraphs. Their aggregate length is 170,000 miles; their total estimated cost is $250,000,000, and the number of messages annually transmitted over them is 6,000,000. Thirteen cables work daily across the Atlantic, and an additional one is being laid from Germany. Messages now go across the Atlantic and are received on the siphon recorder at the rate of fifty words a minute, and at a cost of twenty-five cents a word. Our guns may thunder in the Philippines, and the news by cable, traveling faster than the earth on its axis, may reach the Western Hemisphere under the paradoxical condition of several hours earlier than it occurred. Cablegrams to Manila cost $2.38 a word, and the cable tolls for our War Department alone are costing at the rate of $325,000 a year. The logical outcome is a Pacific cable, a bill for which, connecting San Francisco and Honolulu, has already passed the United States Senate.