Gents Mag 1822 part 2 p.358
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Gentleman's Magazine 1822 part 2 p.358
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The Heliotrope
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The Heliotrope
THE HELIOTROPE, A NEW INSTRUMENT. When Professor Gauss was engaged in 1820 at Luneberg, in trigonometrical observations, to combine the Hanoverian with the Danish triangles, he perceived that when he directed his telescope towards the steeple of St. Michael's Church at Hamburgh, which was seven German (32 English) miles distant, the little round window in the upper part of it reflected the image of the sun towards him, and thus impeded him in his operations. This gave him the idea of using the sun's light for signals, by catching it with a mirror, and reflecting it to the place to which a signal was to be given. He made a calculation of the strength of the sun's light, and of the diminution it suffers in the atmosphere; from which it appeared a small mirror, two or three inches in diameter, was sufficient to reflect the sun's image to the distance of ten or more German miles. This is the Heliotrope, described to be of great imprtance in the measureing of large triangles, and as likely to supersede the methods hitherto employed. These consisted of placing or fastening by night several Argand lamps, with reflectors, at those places which it was intended to observe from a great distance. This measuring by night is very inconvenient, and by day the light of the lamps is much too faint to be always seen at the distance of several miles through a telescope. The inventor of the Heliotrope, on the other hand, had full proof of the great advantage to be derived from it, when he was last year on the summit of the Brocken Mountain, to determmine the three corners of the triangle for measuring the meridian of the North of Germany; on which occasion Professor Gauss gave signals with this instrument to his assistants, stationed at 14 German miles from him, upon the Inselbergh, in the forest of Thuringia. But the great use of the Heliotrope is not confined to such operations. It will be found greatly to excel the telegraph for giving signals, and in time will probably supersede it (provided the Professor could ensure the appearance of the sun). As the reflected image of the sun is visible at so great a distance, the signal stations may be much fewer. the mode of using it is likewise more simple, it being merely necessary alternately to shew and hide the mirror; the intervals, measured by a stop watch, are the signals. |
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