HOW MESSAGES ARE SENT BY THE OCEAN CABLE.

New Zealand Times, Volume XXX, Issue 4579, 23 November 1875, Page 3

HOW MESSAGES ARE SENT BY THE OCEAN CABLE.

(From the Boston Herald.) He (the ocean telegraph operator) taps the “key” as in a land telegraph, only it is a double key. It has two lovers and knobs instead of one. The alphabet used is substantially the same as the Morse alphabet—that is, the different letters are represented by a combination of dashes and dots. For instance, suppose you want to write tho word “ boy.” It would read like this: “—...—• . 15. is one dash and three dots, O, three dashes, and Y, one dash, one dot, and throe dashes. Now, in the laud telegraph tho dashes and tho dots would appear on the strip of paper at the other end of the line, which is unwound from a cylinder, and perforated by a pin at tho end of a bar or armature. If the operator can read by sound, he would dispense with the strip of paper, and read the message by tho “click” of tho armature as it is pulled down and let go by the eleotric magnet. The cable operator, however, has neither of these advantages. There is no paper to perforate, no “ click” of the armature, no armature to “ click.” The is read by means of a moving flash of light upon a polished scale produced by the deflection of a very small mirror which is placed within a “ mirror galvanometer,” which is a small brass cylinder two or three inches in diameter, shaped like a spool or bobbin, composed of several hundred turns of small wire wound with silk to keep the metal from coming in contact. It is wound or coiled exactly like a bundle of now rope, a small hole being left in the middle about tho size of a common wooden pencil. In tho centre of this is suspended a a very thin, delicate mirror about as largo as a kernel of corn, with a correspondingly small

magnet rigidly attached to the back of it. The whole weighs but a little more than a grain, and is suspended by a single fibre of silk, much smaller than a human hair and almost invisible. _ A narrow horizontal scale is placed within a darkened box 2 or 3ft. in front of the mirror, a narrow slit being cut in the centre of the scale to allow a ray of light to shine upon the mirror from a lamp placed behind said scale, the little mirror in turn reflecting the light back upon the scale. This spot of light upon the scale is the index by which all messages are road. The angle through which the ray moves is double that traversed by the mirror itself, and is, therefore, really equivalent to an index 4 or 6ft. in length, without weight. _ To the casual observer there is nothing but a thin ray of light, darting to the right and left with irregular rapidity ; but to the trained eye of thekjperator every flash is replete with intelligence. Thus the word “boy,” already alluded to, would be road in this way; One flash to the right and three to the left is B. Three flashes to the right is 0. One to the right, one to the left, and two more to the right is Y, and so on. Long and constant practice makes the operators wonderfully expert in their profession, and enables them to read from the mirror as readily and as accurately as from a newspaper.