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.
[Illustration: Professor John Milne.
_From a photograph by S. Suzuki, Kudanzaka, Tokio._]
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.
[Illustration: Professor Milne's Sensitive Pendulum, or Seismograph, as
it Appears Enclosed in its Protecting Box.]
[Illustration: The Sensitive Pendulum, or Seismograph, as it Appears
with the Protecting Box Removed.]
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?"
[Illustration: Gifu, Japan, after the Earthquake of 1891.
_This and the pictures following on pages 89, 101, 111, are from
Japanese photographs reproduced in "The Great Earthquake in Japan,
1891," by John Milne and W. K. Burton._]
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.
[Illustration: The Work of the Great Earthquake of 1891 in Neo Valley,
Japan.]
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.
[Illustration: Diagram Showing Vertical and Horizontal Sections of the
More Sensitive of Professor Milne's Two Pendulums, or Seismographs.]
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.
[Illustration: Seismogram of a Borneo Earthquake that Occurred
September 20, 1897.]
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.
[Illustration: Effect of the Great Earthquake of 1891 on the Nagara Gawa
Railway Bridge, Japan.]
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:
[Illustration]
"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:"
[Illustration]
"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.
[Illustration: Pieces of a Submarine Cable Picked Up in the Gulf of
Mexico in 1888.
_The kinks are caused by seismic disturbances, and they show how much
distortion a cable can suffer and still remain in good electrical
condition, as this was found to be._]
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.
[Illustration: Record Made on a Stationary Surface by the Vibrations of
the Japanese Earthquake of July 19, 1891.
_Showing the complicated character of the motion (common to most
earthquakes), and also the course of a point at the centre of
disturbance._]
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.