This Heliograph, or sunwriter, as we may translate the word, consists of little more than a round mirror so mounted that it can easily be turned in every direction. It has a small hole in the centre through which the operator can focus the sun’s rays on any desired spot. This work is further helped by a stick planted in the ground a few yards in front of the mirror. Upon this stick a little rod slides up and down, so that it can be adjusted to any required height. Suppose now that a signal is to be sent to a fort or a lull ten miles away : the mirror is first roughly adjusted to the position, so that flashes can be sent towards the fort; but in order to make all sure, the stick with the slid-ing-rod is placed in front, so that when the observer is looking through the hole at the back of the mirror, this sliding piece just comes in a line with his view of the fort. It therefore acts much in the same manner as that little notch of metal which projects over a gun-barrel, called the sight—it enables the operator to sight the object, and to fire his sun flashes across the country with a true aim, and exactly in the direction of the observers. But supposing that he has .sighted the object, he can do nothing without some method of giving these flashes a meaning, although he might amuse himself at his expense by flashing his signals into their faces, and making them wonder what it all meant. An alphabet composed of short and long flashes is contrived to meet all requirements. Now it is evident that by giving every letter in the alphabet a number, .expressed by this system of shorts and longs, any word could be transmitted, but this would be a most tedious business. A plan has therefore been adopted for reducing both the trouble and time occupied in flashing a message. This plan is founded on the knowledge that there must be certain sentences which in practice are constantly required.—“ Little Folks Magazine.”
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