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Because it was found that a load of about 1,000 lb., made up of men and boys standing outside my observatory wall at a distance of 15 feet from pendulum A, would deflect it 2 mm., the following experiment was made.

In my garden a strong beam was rested on knife edges on the top of a stake driven into the ground. On one end of this a box 1 foot 6 inches square, and 6 inches deep, was hung, so that it could swing freely in a hole cut in the ground. The box was filled with earth which came from the hole, and was covered with turf like the surrounding lawn. This load was balanced by weights suspended at the other end of the beam attached to which there was a pointer moving over a scale. During three fine days it was found that the box lost weight at the rate of about lb. per day per square foot of surface, and as the surface of the material in the box was similar to that of the surrounding ground with which it was level, it was concluded that similar ground in the neighbourhood lost weight at about

the same rate.

During a night the gain by precipitation of dew was sometimes as much as 1.2 oz. per square foot. No doubt many accurate observations have been made on the variation in the rate of evaporation and condensa

tion of moisture from and upon various natural surfaces, but I have not been able to consult them.

In open ground 30 per cent. of the rainfall may percolate, but in a forest as much as 80 per cent. may find its way downwards, the difference being due to evaporation; but as evaporation may cease or even be represented by condensation during the night, it would seem that the volume of water in surface wells especially on hot days following rainy weather might have a daily fluctuation. Such a fluctuation would, however, only account for the rising of water during the night and for an additional rise about midday.

Another point to be noted is the fact that the alternations of evaporation and condensation mean that neighbouring areas, some of which are open and others covered with forest every 12 hours, are unequally relieved of considerable loads. For example, from an area of about 140 feet square in front of my house, which faces south, every day during fine weather about 5 tons of moisture are removed. From the back of the house, which is sheltered from the sun, and where the ground is always damp, comparatively but little is evaporated. The underground chamber is sheltered by a grove of trees on its south and west sides, and on the east side it is open, and pendulum E behaves as if a load were removed from the east side during the morning and afternoon, and that side of the ground had consequently risen. Pendulum A in my house, where there is an evaporation area on the east, south, and partly on the west side, usually behaves like E, to which, however, it is at right angles.

By comparing the table of daily waves with the rainy days when there was no sunshine, when it may be assumed that evaporation was small, as, for example, between March 8 and 11, it will be observed that the daily curves for A and E were not measurable. On sunny days, even if it rained, the curves were pronounced, but they were also large on other days, when, however, evaporation may possibly have been great.

To settle this question future diagrams must be compared with the records obtained from a hygrometer exposed to the open or by two pendulums in parallel positions, but on the opposite sides of a piece of forest land. Two pendulums thus placed ought at the same time to move in opposite directions, that is, during the day each boom ought to move towards the forest.

An observation entirely opposed to what is here suggested is that made by Professor Kortazzi at Nicolaiew, who placed a hydrograph in the cellar where a horizontal pendulum was established, and found that the diagrams given by the two instruments were very similar. This he attributed to the stone column carrying the pendulum behaving like a sponge and absorbing moisture. When the openings to the cellar were closed and the pillar covered with a waterproof material the effect of moisture almost entirely disappeared.

(m) Effects produced by emptying a Well.

To determine what effect a slight disturbance of subterranean water would produce on a horizontal pendulum, on May 21 I employed men to rapidly empty a well which is 104 feet distant in an E.N.E. direction from pendulum A. The well is 42 feet 7 inches deep, 2 feet 7inches in diameter, and on this particular day it contained 13 feet 1 inch, or about 2 tons of

water.

For several days the pointer of the pendulum had been fairly steady, pointing at division 70 on the scale of millimetres. What happened when the well was emptied is given in the table below.

The photographic trace with interruptions in it when the light was removed is shown in fig. 7, Plate II. The movement of the pointer from 70 to 79 indicates a tilt of 136 and the direction of motion was as if a load had been taken away on the well side, and the ground on that side had therefore risen. This may be explained by the fact that as the water came to the surface it was run into a gutter to flow away quickly down a hill. The pendulum remained between 77 and 82 until May 27, when the experiment was repeated. It started at 80, and in 6 hours and 40 minutes it reached 86, and here it has remained with a tendency to get higher but not to return.

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Not only was tilting produced by these operations, but as seen in the photograph tremors were induced.

It might have been anticipated that by emptying the well and the subsequent inflow of water to refill the same-if in consequence of this operation a superficial movement took place-this would have assumed the form of a quaquaversal dip towards the well. What happened was exactly the reverse, from which it may be inferred that the motion of the pendulum was due to the removal of a weight rather than to the movement of the subterranean water.

(n) Earthquakes.

In the last column of the table showing the wandering of pendulums, the number of earthquakes which occurred on various days is given. These are the earthquakes which were recorded by seismographs in Tokio, and it is only one or two of these like the disturbances of March 22, when earth waves were produced, that are recorded by the pendulums. As already stated when speaking of the Kamakura records, although it is probable that most of these shocks were of local origin, this fact cannot be ascertained until the records accumulated at the Meteorological Department have been analysed. Two things, however, are very remarkable, the first being that at about the time of nearly all the shocks, pendulum A has shown abnormally large movements, and secondly there are only three occasions when the movements of A have been moderately

large that earthquakes have not occurred. The tremor storms which were numerous in the early part of the year have no doubt obliterated many of the unfelt earthquakes to which the pendulums were sensitive. Notwithstanding this, there are a considerable number of disturbances on the traces, the record of which must be left for a future report. The most remarkable of these was recorded by pendulum F, which at the time was steady and producing a clear sharp straight line (see fig. 3). This was on June 3, when at 4.36 P.M. the pendulum commenced to move from side to side, and, with the exception of two or three intervals of about five minutes, it continued to move until 10 P.M. Although 14 points of maximum may be counted, the photograph represents what is practically a continuous earthquake of 5 hours 24 minutes' duration. The picture is that of a series of small flat cones, each inverted, with their axes in one straight line. No displacement of the pendulum took place, and after the

FIG. 3.

About half actual size.

The gap at or near noon represents an interval of one hour.

disturbance it continued to draw the same thin line. I do not know where this or the other unfelt earthquakes originated. The rate at which the decided movements are propagated is from 2-5 to 4 kilometres per second, and there are reasons for believing that many of them, like that of March 22, originated beneath the bed of the ocean.

(0) Tremors.

In the extracts from the Journal (pp. 96 to 99) it will be seen that tremors or earth pulsations have often been recorded, and that sometimes these were greater underground than on the surface. During the last two months they have been greater on the surface. Previous analyses have shown that they nearly always accompany a steep barometric gradient. They are sometimes marked when the daily curve is barely visible, but small tremors at least usually accompany these waves, and they are more pronounced during the night and early morning, when the rate at which a pendulum is being displaced is relatively slow. The fact that small tremors were produced at the time the well was emptied is a fact not to be overlooked when considering their origin.

I regret to say that a more careful examination of the tremor records must be left for a future report.

(p) Observations at Yokohama and Kanagawa.

As already stated, the instruments at Kanagawa (1) and (G and H) at Yokohama are underground, and stand on short brick columns rising from soft tuff rock. The softness of this rock may be judged of from the fact that when a person stands near one of the columns, the boom of the pendulum is deflected from 5 to 17 mm., from which it appears that, as a foundation to resist loading effects, the tuff rock is no better than a slab of concrete on the alluvium in Tokio. Owing to the collapse of the roof of the Yokohama cave, which caused a delay of two weeks, and owing to the fact that the clocks have been continually stopping, and good clocks cannot be found

in Tokio or Yokohama, the records from this place are extremely few. Those which have been obtained, extending over two or three days, show straight lines like fig. 1, Plate II. There are neither daily curves nor tremors.

From Kanagawa, although the cave is very wet and the conditions for observing very unfavourable, for about two months everything has worked satisfactorily. Like the Kamakura records they do not show tremors or daily waves, but they do show unfelt earthquakes and wandering. For example, on May 5 the boom moved as if by a N.E. tilting as much as 14". This it reached on May 7. From this date it slowly returned to its starting point, which it reached on May 12. Small shocks occurred on the 2nd, 4th, and 6th.

(q) Conclusions.

Inasmuch as the analysis of materials already accumulated is not yet completed, and as certain experiments require to be repeated or amplified, it is premature to formulate definite conclusions. All that can therefore be done is to outline the form which conclusions may possibly assume.

Although I understand that Italian observers have found that tremors are as marked underground, even on the rock, as they are on the surface in Japan, this seems to be only true for the alluvium. Underground on the rock at three stations, with such instruments as I have employed, there has not been even an indication of tremors. Neither have daily waves been observed. All the pendulums, whether on the rock or on the alluvium, from time to time leave their normal position, moving for two or three days in one direction and then slowly returning. These movements, which have been called wanderings, sometimes indicate a tilting of as much as 14". Because these movements have often been accompanied by local earthquakes, it seems possible that they may actually represent rock bending, the earthquakes announcing the fact that resistances to the process are being overcome.

Some of the wanderings noted on the alluvium may possibly be attributed to disturbances in the subterranean circulation of water after rainfall.

Although the daily movement of the pendulums has been most marked by those which are nearest to water level, because they only show a single wave during the day, while the water in a neighbouring well rises and falls twice during the 24 hours, the daily wave cannot altogether be attributed to the movement of subterranean water. Because certain diagrams have shown a superimposed wave, it is possible that the character of the daily wave may now and then be influenced by subterranean water. Because a wave may be produced by relieving an area in the vicinity of a pendulum of a load, as, for example, by taking 2 tons of water out of a well which is 104 feet distant from pendulum A, and pouring the water away down a slope, it seems likely that the daily wave is produced by an action of this description. The action suggested is that which takes place every day when the sun shines or the wind blows across ground which is open and that which is covered, for example, by forests or buildings. By evaporation one area is rapidly relieved of a load, while the adjacent area loses but little. For example, experiment shows that on fine days an open grass-covered area 140 feet square in front of my house, which is 120 feet long and runs E. and W., loses in 12 hours about 5 tons of moisture. At the back of the house, where the ground is sheltered from the sun, evaporation is small. As confirming this view it

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