CHAPTER III

THE EARTHQUAKE MEASURER

_Professor John Milne's Seismograph_

Of all strange inventions, the earthquake recorder is certainly one of the most remarkable and interesting. A terrible earthquake shakes down cities in Japan, and sixteen minutes later the professor of earthquakes, in his quiet little observatory in England, measures its extent--almost, indeed, takes a picture of it. Actual waves, not unlike the waves of the sea blown up by a hurricane, have travelled through or around half the earth in this brief time; vast mountain ranges, cities, plains, and oceans have been heaved to their crests and then allowed to sink back again into their former positions. And some of these earthquake waves which sweep over the solid earth are three feet high, so that the whole of New York, perhaps, rises bodily to that height and then slides over the crest like a skiff on an ocean swell.

At first glance this seems almost too strange and wonderful to believe, and yet this is only the beginning of the wonders which the earthquake camera--or the seismograph (earthquake writer, as the scientists call it)--has been disclosing.

The earthquake professor who has worked such scientific magic is John Milne. He lives in a quaint old house in the little Isle of Wight, not far from Osborne Castle, where Queen Victoria made her home part of the year. Not long ago he was a resident of Japan and professor of seismology (the science of earthquakes) at the University of Tokio, where he made his first discoveries about earthquakes, and invented marvellously delicate machines for measuring and photographing them thousands of miles away. Professor Milne is an Englishman by birth, but, like many another of his countrymen, he has visited some of the strangest nooks and corners of the earth. He has looked for coal in Newfoundland; he has crossed the rugged hills of Iceland; he has been up and down the length of the United States; he has hunted wild pigs in Borneo; and he has been in India and China and a hundred other out-of-the-way places, to say nothing of measuring earthquakes in Japan. Professor Milne laid the foundation of his unusual career in a thorough education at King's College, London, and at the School of Mines. By fortunate chance, soon after his graduation, he met Cyrus Field, the famous American, to whom the world owes the beginnings of its present ocean cable system. He was then just twenty-one, young and raw, but plucky. He thought he was prepared for anything the world might bring him; but when Field asked him one Friday if he could sail for Newfoundland the next Tuesday, he was so taken with astonishment that he hesitated, whereupon Field leaned forward and looked at him in a way that Milne has never forgotten.

"My young friend, I suppose you have read that the world was made in six days. Now, do you mean to tell me that, if this whole world was made in six days, you can't get together the few things you need in four?"

And 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.

It is difficult to realise how very sensitive these earthquake pendulums really are. They will indicate the very minutest changes in the earth's level--as slight as one inch in ten miles. A pair of these pendulums placed on two buildings at opposite sides of a city street would show that the buildings literally lean toward each other during the heavy traffic period of the day, dragged over from their level by the load of vehicles and people pressing down upon the pavement between them. The earth is so elastic that a comparatively small impetus will set it vibrating. Why, even two hills tip together when there is a heavy load of moisture in a valley between them. And then when the moisture evaporates in a hot sun they tip away from each other. These pendulums show that.

Nor are these the most extraordinary things which the pendulums will do. G. K. Gilbert, of the United States Geological Survey, argues that the whole region of the great lakes is being slowly tipped to the southwest, so that some day Chicago will sink and the water outlet of the great fresh-water seas will be up the Chicago River toward the Mississippi, instead of down the St. Lawrence. Of course this movement is as slow as time itself--thousands of years must elapse before it is hardly appreciable; and yet Professor Milne's instruments will show the changing balance--a marvel that is almost beyond belief. Strangely enough, sensitive as this special instrument is to distant disturbances, it does not swerve nor quiver for near-by shocks. Thus, the blasting of powder, the heavy rumbling of wagons, the firing of artillery has little or no effect in producing a movement of the boom. The vibrations are too short; it requires the long, heavy swells of the earth to make a record.

Professor Milne tells some odd stories of his early experiences with the earthquake measurer. At one time his films showed evidences of the most horrible earthquakes, and he was afraid for the moment that all Japan had been shaken to pieces and possibly engulfed by the sea. But investigation showed that a little grey spider had been up to pranks in the box. The spider wasn't particularly interested in earthquakes, but he took the greatest pleasure in the swinging of the boom, and soon began to join in the game himself. He would catch the end of the boom with his feelers and tug it over to one side as far as ever he could. Then he would anchor himself there and hold on like grim death until the boom slipped away. Then he would run after it, and tug it over to the other side, and hold it there until his strength failed again. And so he would keep on for an hour or two until quite exhausted, enjoying the fun immensely, and never dreaming that he was manufacturing wonderful seismograms to upset the scientific world, since they seemed to indicate shocking earthquake disasters in all directions.

Mr. Cleveland Moffett, to whom I am indebted for much of the information contained in this chapter, tells how the reporters for the London papers rush off to see Professor Milne every time there is news of a great earthquake, and how he usually corrects their information. In June, 1896, for instance, the little observatory was fairly besieged with these searchers for news.

"This earthquake happened on the 17th," said they, "and the whole eastern coast of Japan was overwhelmed with tidal waves, and 30,000 lives were lost."

"That last is probable," answered Professor Milne, "but the earthquake happened on the 15th, not the 17th;" and then he gave them the exact hour and minute when the shocks began and ended.

"But our cables put it on the 17th."

"Your cables are mistaken."

And, sure enough, later despatches came with information that the destructive earthquake had occurred on the 15th, within half a minute of the time Professor Milne had specified. There had been some error of transmission in the earlier newspaper despatches.

Again, a few months later, the newspapers published cablegrams to the effect that there had been a severe earthquake at Kobe, with great injury to life and property.

"That is not true," said Professor Milne. "There may have been a slight earthquake at Kobe, but nothing that need cause alarm."

And the mail reports a few weeks later confirmed his reassuring statement, and showed that the previous sensational despatches had been grossly exaggerated.

Professor Milne is also the man to whose words cable companies lend anxious ear, for what he says often means thousands of dollars to them. Early in January, 1898, it was officially reported that two West Indian cables had broken on December 31, 1897.

"That is very unlikely," said Professor Milne; "but I have a seismogram showing that these cables may have broken at 11.30 A.M. on December 29, 1897." And then he located the break at so many miles off the coast of Haiti.

This sort of thing, which is constantly happening, would look very much like magic if Professor Milne had kept his secrets to himself; but he has given them freely to all the world.

Professor Milne has learned from his experiments that the solid earth is full of movements, and tremors, and even tides, like the sea. We do not notice them, because they are so slow and because the crests of the waves are so far apart. Professor Milne likes to tell, fancifully, how the earth "breathes." He has found that nearly all earthquake waves, whether the disturbance is in Borneo or South America, reach his laboratory in sixteen minutes, and he thinks that the waves come through the earth instead of around it. If they came around, he says, there would be two records--one from waves coming the short way and one from waves coming the long way round. But there is never more than a single record, so he concludes that the waves quiver straight through the solid earth itself, and he believes that this fact will lead to some important discoveries about the centre of our globe. Professor Milne was once asked how, if earthquake waves from every part of the earth reached his observatory in the same number of minutes, he could tell where the earthquake really was.

"I may say, in a general way," he replied, "that we know them by their signatures, just as you know the handwriting of your friends; that is, an earthquake wave which has travelled 3,000 miles makes a different record in the instruments from one that has travelled 5,000 miles; and that, again, a different record from one that has travelled 7,000 miles, and so on. Each one writes its name in its own way. It's a fine thing, isn't it, to have the earth's crust harnessed up so that it is forced to mark down for us on paper a diagram of its own movements?"

He took pencil and paper again, and dashed off an earthquake wave like this:

"There you have the signature of an earthquake wave which has travelled only a short distance, say 2,000 miles; but here is the signature of the very same wave after travelling, say, 6,000 miles:"

"You see the difference at a glance; the second seismogram (that is what we call these records) is very much more stretched out than the first, and a seismogram taken at 8,000 miles from the start would be more stretched out still. This is because the waves of transmission grow longer and longer, and slower and slower, the farther they spread from the source of disturbance. In both figures the point A, where the straight line begins to waver, marks the beginning of the earthquake; the rippling line AB shows the preliminary tremors which always precede the heavy shocks, marked C; and D shows the dying away of the earthquake in tremors similar to AB.

"Now, it is chiefly in the preliminary tremors that the various earthquakes reveal their identity. The more slowly the waves come, the longer it takes to record them, and the more stretched out they become in the seismograms. And by carefully noting these differences, especially those in time, we get our information. Suppose we have an earthquake in Japan. If you were there in person you would feel the preliminary tremors very fast, five or ten in a second, and their whole duration before the heavy shocks would not exceed ten or twenty seconds. But these preliminary tremors, transmitted to England, would keep the pendulums swinging from thirty to thirty-two minutes before the heavy shocks, and each vibration would occupy five seconds.

"There would be similar differences in the duration of the heavy vibrations; in Japan they would come at the rate of about one a second: here, at the rate of about one in twenty or forty seconds. It is the time, then, occupied by the preliminary tremors that tells us the distance of the earthquake. Earthquakes in Borneo, for instance, give preliminary tremors occupying about forty-one minutes, in Japan about half an hour, in the earthquake region east of Newfoundland about eight minutes, in the disturbed region of the West Indies about nineteen or twenty minutes, and so on. Thus the earthquake is located with absolute precision."

Most earthquakes occur in the deep bed of the ocean, in the vast valleys between ocean mountains, and the dangerous localities are now almost as well known as the principal mountain ranges of North America. There is one of these valleys, or ocean holes, off the west coast of South America from Ecuador down; there is one in the mid-Atlantic, about the equator, between twenty degrees and forty degrees west longitude: there is one at the Grecian end of the Mediterranean; one in the Bay of Bengal, and one bordering the Alps; there is the famous "Tuscarora Deep," from the Philippine Islands down to Java; and there is the North Atlantic region, about 300 miles east of Newfoundland. In the "Tuscarora Deep" the slope increases 1,000 fathoms in twenty-five miles, until it reaches a depth of 4,000 fathoms.

And this brings us to the consideration of one of the greatest practical advantages of the seismograph--in the exact location of cable breaks. Indeed, a large proportion of these breaks are the result of earthquakes. In a recent report Professor Milne says that there are now about twenty-seven breaks a year for 10,000 miles of cable in active use. Most of these are very costly, fifteen breaks in the Atlantic cable between 1884 and 1894 having cost the companies $3,000,000, to say nothing of loss of time. And twice it has happened in Australia (in 1880 and 1888) that the whole island has been thrown into excitement and alarm, the reserves being called out, and other measures taken, because the sudden breaking of cable connections with the outside world has led to the belief that military operations against the country were preparing by some foreign power. A Milne pendulum at Sydney or Adelaide would have made it plain in a moment that the whole trouble was due to a submarine earthquake occurring at such a time and such a place. As it was, Australia had to wait in a fever of suspense (in one case there was a delay of nineteen days) until steamers arriving brought assurances that neither Russia nor any other possibly unfriendly power had begun hostilities by tearing up the cables.

There have been submarine earthquakes in the Tuscarora, like that of June 15, 1896, that have shaken the earth from pole to pole; and more than once different cables from Java have been broken simultaneously, as in 1890, when the three cables to Australia snapped in a moment. And the great majority of breaks in the North Atlantic cables have occurred in the Newfoundland hollow, where there are two slopes, one dropping from 708 to 2,400 fathoms in a distance of sixty miles, and the other from 275 to 1,946 fathoms within thirty miles. On October 4, 1884, three cables, lying about ten miles apart, broke simultaneously at the spot. The significance of such breaks is greater when the fact is borne in mind that cables frequently lie uninjured for many years on the great level plains of the ocean bed, where seismic disturbances are infrequent.

The two chief causes of submarine earthquakes are landslides, where enormous masses of earth plunge from a higher to a lower level, and in so doing crush down upon the cable, and "faults," that is, subsidences of great areas, which occur on land as well as at the bottom of the sea, and which in the latter case may drag down imbedded cables with them.

It is in establishing the place and times of these breaks that Professor Milne's instruments have their greatest practical value; scientifically no one can yet calculate their value.

In addition to the first instrument set up by Professor Milne in Tokio in 1883, which is still recording earthquakes, there are now in operation about twenty other seismographs in various parts of the world, so that earthquake information is becoming very accurate and complete, and there is even an attempt being made to predict earthquakes just as the weather bureau predicts storms. In any event Professor Milne's invention must within a few years add greatly to our knowledge of the wonders of the planet on which we live.