The Calcutta Earthquake

Abstract

IN a previous number of NATURE (June 24, vol. lvi. p. 174), Mr. T. Heath gave an account, re the Indian earthquake, of the oscillations set up in the bifilar pendulum of the Edinburgh Observatory between the times June 11, 23h. 18m., and June 12, oh. 33m. The reproduction of the photographic record accompanying the letter did not, however, show any of the minor details of the effect produced. We have received a communication from Prof. P. Blaserna, in which these details are clearly depicted on the records obtained with the instruments erected at the Royal Geodetic Observatory of Rocca di Papa (Rome). The curves here shown illustrate the movements of the N.–S. (Fig. 1), and the E.–W. (Fig. 2) components of a horizontal pendulum, and show better than any description the increase and decrease in the length of swing of the pendulum at the times (intervals of ten minutes) indicated by the short arrows. We may mention that a second set of curves, made with another quite independent instrument (seismometograph with a vertical pendulum carrying a mass of 200 kilograms), recorded nearly similar disturbances at the same times. This latter instrument is also situated at Rocca di Papa, and directed by Dr. A. Cancani. The above curves, besides indicating the effect produced by the shocks caused by the Calcutta earthquake, show how very efficient the Roman instruments are for recording the minute details of the earth's movements.