SKPTBMr.ER 1, 1900.] 



KNOW LEDGE. 



lor 



current flows in the opposite direction, viz., through the 

 earth to the distant station, and back, through the 

 trunk wire, to the battery. Tiie holes in the paper are 

 so arranged that onlj* one brusli can touch the cylinder 

 at one time. So. according to the arrangement of the 



E F 



G 



r — > 





FiO. 2. — Diagram of the seuding apparatiisof the Polhik-A'iraj; 

 Telosrraph. A. Trunk or line wire ; B. Earth or return wire ; 

 C. Metal evliuder ; I). Batterv; E. Positive eleetrode or brush: 

 F. Xesjative electrode or brash ; G. Perforated sending slip ; 

 H. Self-induetion Coil for neutralising inductive disturbances 

 on line. 



holes on the paper ribbon, we have currents sent to the 

 far-away office which sometimes ilow in one direction 

 and sometimes in the other. A large number of clerks 

 prepare the paper ribbons, and the sending apparatus 

 can be fed at the pace required. This is extremely 

 simple and easily followed on the illustration. 



Now as to the receiving arrangements. These consist, 

 first, of a fairly powerful bar-magnet fixed in a kind of 

 box having one side composed of thin metal, or ferro- 

 type. The magnet is fixed in such a manner that it 

 draws in the metal side to a slight degree. Round that 

 part of the magnet which is near the metal side, or 

 diaphragm, of the box. is fixed a coil of fine wire. The 



B - 



Fig. .3. — Diagram of the reeeiving apparatus of the PoUak- 

 Virag Telegrapli. A. Trunk or line wire ; B. Earth or return 

 wire ; C. Condenser for neutralising disturbances due to the 

 " Capacity " of the line ; D. Coil; Sp. Mirror; L. Electric glow- 

 lamp ; T. Drum of sensitized paper. 



disposition of these parts can be easily distinguished 

 in Fig. 3. Remembering what has been said above 

 about the effect of an electric current on a magnet, we 

 can see what would be the result of a current passed 

 through the coil of wire fixed on the end of this magnet. 

 The end of the magnet near the diaphragm is a north 



pole. The wire on the coil is wound in such a way that 

 when the current Hows from A to B the power is in- 

 creased, whilst when it flows from B to A the power is 

 decreased. The result of increasing llie power of the 

 magnet is to draw the metal diaphragm nearer, whilst 

 if the power is decreased, the diaphragm is released, 

 and draws away from the magnet. With the sending 

 apparatus previously described the ciirrcnt is sent some- 

 times in one direction and sometimes in the other. 

 The diaphragm answers to this change in the direction 

 of the current by swerving towards or away from the 

 magnet. But at the pace of 100.000 words per hour, 

 the diaphragm would move '2G.400 times per minute. 

 So some means had to be devised to register these move- 

 ments in an intelligible way. This is done by enlisting 

 the aid of photography in the following ingenious way. 



In front of the diaphragm is fixed a large magnet 

 made in a peculiar manner. It is curled round some- 

 what like a horse-shoe. One end of it is cut into two 

 points, the other end into a pointed weak spring. A tiny 

 mirror (Fig. ■"?, Sp) with a .small plate of iron fastened to 

 its back is suspended to the two-pointed end, which holds 

 it by magnetic attraction. The spring end of thc 



FlO. 4.— The words " Lord Roberts " as they would appear 

 when written in the Morse code by (he Polbik-Virag Telegrajib. 



magnet touches another tiny iron plate on the back of 

 the mirror. A very small light metal rod is fixed to 

 the middle of the diaphragm, and to the spring end of 

 the magnet. Now if the diaphragm moves, this rod 

 communicates the movement to tlie spring, which in 

 turn moves the mirror. The two-pointed end of the 

 magnet acts as a sort of hinge with practically no 

 friction, upon which the mirror swings. 



Some little distance from the mirror, a small electric 

 glow-lamp is placed, which throws a light on to the 

 reflecting surface. This light is reflected on to a drum 

 covered by sensitized paper. These details can be 

 easily followed in Fig. 3. 



When the diaphragm is drawn inwards the lower 

 end of the mirror is drawn back and the light ray is 

 depressed. When the diaphragm moves away from the 

 bar-magnet the lower end of the mirror is thrust for- 

 ward and the light ray is raised. This results in a 

 line on the sensitized paper, which rises sometimes in 

 waves above the central line, and is sometimes depressed 

 in waves below the central line. The waves above the 

 line represent the " dashes " of the Morse alphabet, 

 those below represent the dots. In Fig. 4 the 

 words " Lord Roberts " are given as they would be 

 indicated by these waves. After the message has been 

 sent, the sensitized paper is taken from the drum and 

 the marks are " fixed," a process occupying about two 

 minutes, and then the message is ready to be written 

 up by a clerk.* 



• Herr PoUak writes to me as follows :— ' We are now using endless 

 slips and diagonal writing combined with an automatic system of 

 develojiment, so that messages are ready for transcrijition immediately 

 on receipt." 



