Boys' Second Book of Inventions. Baker Ray Stannard
Milne sailed the next Tuesday to begin his lifework among the rough hills of Newfoundland. Then came an offer from the Japanese Government, and he went to the land of earthquakes, little dreaming that he would one day be the greatest authority in the world on the subject of seismic disturbances. His first experiments – and they were made as a pastime rather than a serious undertaking – were curiously simple. He set up rows of pins in a certain way, so that in falling they would give some indication as to the wave movements in the earth. He also made pendulums made of strings with weights tied at the end, and from his discoveries made with these elementary instruments, he planned earthquake-proof houses, and showed the engineers of Japan how to build bridges which would not fall down when they were shaken. So highly was his work regarded that the Japanese made him an earthquake professor at Tokio and supplied him with the means for making more extended experiments. And presently we find him producing artificial earthquakes by the score. He buried dynamite deep in the ground and exploded it by means of an electric button. The miniature earthquake thus produced was carefully measured with curious instruments of Professor Milne's invention. At first one earthquake was enough at any one time, but as the experiments continued, Professor Milne sometimes had five or six earthquakes all quaking together; and once so interested did he become that he forgot all about the destructive nature of earthquakes, and ventured too near. A ton or more of earth came crashing down around him, half burying him and smashing his instruments flat. All this made the Japanese rub their eyes with astonishment, and by and by the Emperor heard of it. Of course he was deeply interested in earthquakes, because there was no telling when one might come along and shake down his palace over his head. So he sent for Professor Milne, and, after assuring himself that these experimental earthquakes really had no serious intentions, he commanded that one be produced on the spot. So Professor Milne laid out a number of toy towns and villages and hills in the palace yard with a tremendous toy earthquake underneath. The Emperor and his gayly dressed followers stood well off to one side, and when Professor Milne gave the word the Emperor solemnly pressed a button, and watched with the greatest delight the curious way in which the toy cities were quaked to earth. And after that, this surprising Englishman, who could make earthquakes as easily as a Japanese makes a lacquered basket, was held in high esteem in Japan, and for more than twenty years he studied earthquakes and invented machines for recording them. Then he returned to his home in England, where he is at work establishing earthquake stations in various parts of the world, by means of which he expects to reduce earthquake measurement to an exact science, an accomplishment which will have the greatest practical value to the commercial interests of the world, as I shall soon explain.
But first for a glimpse at the curious earthquake measurer itself. To begin with, there are two kinds of instruments – one to measure near-by disturbances, and the second to measure waves which come from great distances. The former instrument was used by Professor Milne in Japan, where earthquakes are frequent; the latter is used in England. The technical name for the machine which measures distant disturbances is the horizontal pendulum seismograph, and, like most wonderful inventions, it is exceedingly simple in principle, yet doing its work with marvellous delicacy and accuracy.
In brief, the central feature of the seismograph is a very finely poised pendulum, which is jarred by the slightest disturbance of the earth, the end of it being so arranged that a photograph is taken of every quiver. Set a pendulum clock on the dining-table, jar the table, and the pendulum will swing, indicating exactly with what force you have disturbed the table. In exactly the same way the delicate pendulum of the earthquake measurer indicates the shaking of the earth.
The accompanying diagram gives a very clear idea of the arrangement of the apparatus. The "boom" is the pendulum. It is customary to think of a pendulum as hanging down like that of a clock, but this is a horizontal pendulum. Professor Milne has built a very solid masonry column, reaching deep into the earth, and so firmly placed that nothing but a tremor of the hard earth itself will disturb it. Upon this is perched a firm metal stand, from the top of which the boom or pendulum, about thirty inches long, is swung by means of a "tie" or stay. The end of the boom rests against a fine, sharp pivot of steel (as shown in the little diagram to the right), so that it will swing back and forth without the least friction. The sensitive end of the pendulum, where all the quakings and quiverings are shown most distinctly, rests exactly over a narrow roll of photographic film, which is constantly turned by clockwork, and above this, on an outside stand, there is a little lamp which is kept burning night and day, year in and year out. The light from this lamp is reflected downward by means of a mirror through a little slit in the metal case which covers the entire apparatus. Of course this light affects the sensitive film, and takes a continuous photograph of the end of the boom. If the boom remains perfectly still, the picture will be merely a straight line, as shown at the extreme right and left ends of the earthquake picture on this page. But if an earthquake wave comes along and sets the boom to quivering, the picture becomes at once blurred and full of little loops and indentations, slight at first, but becoming more violent as the greater waves arrive, and then gradually subsiding. In the picture of the Borneo earthquake of September 20, 1897, taken by Professor Milne in his English laboratory, it will be seen that the quakings were so severe at the height of the disturbance that nothing is left in the photograph but a blur. On the edge of the picture can be seen the markings of the hours, 7.30, 8.30, and 9.30. Usually this time is marked automatically on the film by means of the long hand of a watch which crosses the slit beneath the mirror (as shown in the lower diagram with figure 3). The Borneo earthquake waves lasted in England, as will be seen, two hours fifty-six minutes and fifteen seconds, with about forty minutes of what are known as preliminary tremors. Professor Milne removes the film from his seismograph once a week – a strip about twenty-six feet long – develops it, and studies the photographs for earthquake signs.
Besides this very sensitive photographic seismograph Professor Milne has a simpler machine, not covered up and without lamp or mirror. In this instrument a fine silver needle at the end of the boom makes a steady mark on a band of smoked paper, which is kept turning under it by means of clockwork. A glance at this smoked-paper record will tell instantly at any time of day or night whether the earth is behaving itself. If the white line on the dark paper shows disturbances, Professor Milne at once examines his more sensitive photographic record for the details.
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