The method adopted is simple and beautiful, — a modification of the Wheatstone system. The message is first punched as a series of holes in a paper tape. This perforated tape is then run through an automatic transmitter, and by means of a system of small levers the re quired signals are transmitted at any desired speed. The operator has a wooden stick in each hand with which he strikes one or other of the three keys of the small perforator directly in front of him. One key punches a right-hand hole, another key a left-hand hole and the mid dle key makes a space. In this way the cable gram before him is transmitted at the rate of about 20 words a minute into a perforated tape. From the perforator the tape runs into an au tomatic transmitter, or °auto.* There is a row of small central holes in the tape, and on each side is a row of larger holes. The latter rep resent the message. A small star wheel in the °auto' engages with the central line of holes and feeds the tape along at a uniform rate. A couple of small steel rods about the size of a knitting-needle, one for each of the two rows of message holes, continually vibrate against the paper. When either of them enters a per foration in the paper, a lever connected with it moves and makes an electric contact, sending a short, sharp signal into the cable.
Cable Recently several still more wonderful inventions have been perfected. On land relays are used. For instance, messages from New York to Chicago are automatically repeated at Buffalo or Meadville and by auto matic repeating every 600 or 800 miles tt is an every-day occurrence to telegraph direct be tween New York and San Francisco. A relay capable of performing similar work for cables has been a dream of cable engineers and in ventors for years, and in default of such an instrument °human relays' have been em ployed; that is, at the end of one section of a cable an operator takes the paper record of a cablegram as it comes from the siphon recorder and retransmits it.
. But the cable relay is now an accomplished fact. The only hope of constructing such an instrument was to utilize the siphon recorder. One difficulty has been that the movements of the siphon, as shown by the paper records, have till recently been most irregular. There has been what photographers would describe as °lack of definition' about the signals, rendering it hopeless to attempt to relay them automatic ally by machinery. The first thing to do was, therefore, to straighten and sharpen up the sig nals a bit, and a very able group of cable engi neers, including H. A. C. Saunders, electrician in-chief of the Eastern and associate cable companies, his assistant, Walter Judd, with Dr. Muirhead, inventor of the cable duplex, and Messrs. Brown and Dearlove, succeeded in sharpening them. They secured very regular signals, usually described as °square signals.'
This result was obtained by means too techni cal to be described here, but the chief device used is known as an °inductive shunt.° Having squared the signals, it was now possible, though by no means easy, to construct a cable relay. Two have been perfected. One is known as the Brown & Dearlove relay, the principal inventor of it being S. G. Brown. The other has been invented by Dr. Muirhead. In both a fine wire terminating in a platinum contact-point takes the place of the IA in the siphon of a re corder. The contact-point instead of resting on the paper tape rests on a rapidly moving metal lic surface divided into two parts. In the Brown & Dearlove relay this contact-surface consists of a constantly revolving metallic drum or wheel. The siphon, with its wire and con tact-point, °skates,-° as the inventor describes it, with the utmost freedom on the periphery of this wheel. The drum looks like a phonograph cylinder. As the siphon skates upon the right or left half of this drum it makes a positive or a negative electric contact and automatically transmits a corresponding signal with renewed energy into the next section of cable. In the Muirhead relay the moving metallic surface consists of a small plate vibrating rapidly. The result is the same. Able in this way to make definite electrical contacts through a long ocean cable, an operator can easily work, by means of these contacts, local apparatus moved by more powerful currents. In this way both Mr. Brown and Dr. Muirhead have devised perfora tors which reproduce at the receiving station perforated tape identical with that used for transmitting the message at the sending station. This tape is available for transmission through an this plan having the advantage that the signals are retransmitted in as perfect form as the original signals; and, theoretically at any rate, the process may be repeated indefinitely, so that it would be possible to send a cable mes sage automatically through a dozen stations from England to Australia. This will no doubt be done in time, but it is a very slow process getting such complicated and delicate inventions Into commercial use. It is a question of time and growth. The Brown & Dearlove relay has been adopted by the Eastern Company, and has been in commercial use. Dr. Muirhead's relay has also proved very successful in several long distance tests.
Cable Statistics.— In all there are now about 291,000 nautical miles of submarine cables, enough to go about 13 times around the globe. They have cost about $250,000,000, but their market value is considerably higher, as deep-sea cables are solid and profitable investments. All told there are about 50 cable steamers in the world, including those owned by the cable-con struction companies and governments, with gross tonnage of perhaps 85,000 tons.