For some hours after the earthquake, shocks were so frequent in the meizoseismal area that the ground in places hardly ever ceased from trembling. Without instrumental aid, detailed record was of course impossible; but fortunately the buried seismographs at Gifu and Nagoya were uninjured, and in about seven hours both were once more in working order. To the energy by which this result was accomplished, we owe our most valuable registers of the after-shocks of a great earthquake. [Illustration: FIG. 52.--Monthly frequency of after-shocks at Gifu. (_Omori._)] Until the end of 1893--that is, in little more than two years--the total number of shocks recorded at Gifu was 3,365, and at Nagoya 1,298. None of these approached the principal earthquake in severity. Nevertheless, of the Gifu series, 10 were described as violent and 97 strong; while of the remainder, 1,808 were weak, 1,041 feeble, and 409 were sounds alone without any accompanying shock. The slight intensity of most of the shocks is also evident from the inequality in the numbers recorded at Gifu and Nagoya, from which it appears that nearly two-thirds were imperceptible more than about 25 miles from the chief origin of the shocks. Only 70 of the after-shocks during the first two years were registered at Osaka, and not more than 30 at Tokio. _Distribution of After-shocks in Time._--The decline in frequency of the after-shocks was at first extremely rapid, the numbers recorded at Gifu during the six days after the earthquake being 303, 147, 116, 99, 92, and 81, and at Nagoya 185, 93, 79, 56, 30, and 31; in fact, half of the shocks up to the end of 1893 occurred by November 23rd at Gifu, and by November 6th at Nagoya. The daily numbers at these two places are represented in Fig. 51, in which the crosses correspond to the numbers at Gifu, and the dots to those at Nagoya; and the curves drawn through or near the marks represent the average daily number of shocks from October 29th to November 20th. It will be seen that these curves are hyperbolic in form, the change from very rapid to very gradual decline in frequency taking place from five to ten days after the great earthquake. Fig. 52 illustrates the distribution in time of the after-shocks at Gifu to the end of 1893, the ordinates in these cases representing the number of shocks during successive months.[57]