IJ4. REPORT 1860. 



A few Corals have been recorded from the Upper Lias, but they are smaller and less 

 frequent than the above. 



On the Velocity of Earthquake Shocks in the Laterite of India. 

 By John Allan Broun, F.R.S. 



Mr. Mallet's interesting observations on the velocity of earthquake shocks had 

 drawn my attention to the subject ; and when earthquakes were remarked in Travan- 

 core, the part, South of India, where I resided, I endeavoured to add something to 

 our knowledge of the subject. 



Four earthquakes were perceived in Travancore during the year 1856; that to 

 which I am about to allude was observed at the Trevandrum Observatory, August 22, 

 where the commencement of the shock was noted accurately by the Observatory 

 clock, at 4 b 25 m 10 s of Trevandrum mean time. The magnets in the magnetic 

 observatory were dancing up and down with sharp jerks, but without any change 

 of mean positions ; a vessel containing water was wetted highest on the points to 

 W.N.W. and E.S.E. The vibration of the bifilar magnet was 3"0 scale divisions a 

 few minutes after the shock. On the 11th of the same month a shock had been 

 felt at Trevandrum, and I had addressed a circular to several persons in the district 

 for information as to the time, direction, and character of the shock : this circular 

 had drawn attention to the questions of interest in connexion with such shocks. 

 One gentleman at Quilon (thirty-seven miles N.W. of Trevandrum) was writing 

 an account of the former shock when the shock of August 22nd occurred. Four 

 gentlemen and one lady noted the time of the shock at Quilon ; these times were 

 as follows:— Mr. D'Albed'yhll and Mr. Newas (same watch), 4 h 20™; Capt. Carr, 

 4t> 25 m - Mr. Stone, 4 h 19 m ; Mrs. Wilkins, 4 h I6 m . A box chronometer by Dent 

 was sent by me to Quilon, for the purpose of comparing it with the different 

 watches or clocks used in the determination of the time of the shock : the rate of the 

 chronometer was +8 seconds, and the error was determined before and after the 

 comparisons, which were made August 27th. The following are the facts connected 

 wth the observations: — Mr. Newas had set his watch, on the 17th of August, to 

 6 h m at sunrise ; allowing for the height of the chain of Ghats where the sun rose, 

 I have computed that sunrise must have been about 3 minutes before six o'clock : 

 the watch had been allowed to run down after the shock, so that it could not be 

 compared with the chronometer. Supposing the watch without any marked rate, 

 the Trevandrum mean time of the shock was 4 h 18£ m . Mr. Stone had set his watch 

 August 17, bv the time of the Trevandrum Observatory (where a ball is dropped 

 daily at eleven o'clock) . When compared with the chronometer, it had gained 3 m 35 s 

 giving a daily rate of about +21 s, 5; so that on the 22nd the error of the watch 

 roust have been about l m 47% and the shock must have occurred about 4" 17i m 

 Trevandrum mean time. This is by far the most important observation ; the others 

 can be considered only as approximate determinations. Capt. Carr's watch was 

 found fourteen minutes fast of Trevandrum time on the 27th ; supposing the rate 

 zero the time of shock was 4 h ll m . Mrs. Wilkins's clock had been compared with 

 the mess clock of the native regiment at Quilon, which was regulated by persons 

 proceeding from Trevandrum, with the Observatory time, and which was found 

 correct when compared with the chronometer. Mrs. Wilkins's clock was three mi- 

 nutes slow of Trevandrum mean time, making the time of the clock 4 h 19 ra . The 

 four observations, therefore, corrected to Trevandrum mean time, gave— 



h m 



Mr. Newas 4 18 2 



„ Stone 4 17i 



Capt. Carr 4 11 



There can be no doubt that Mr. Stone's observation is the most trustworthy, as 

 his time depends on two comparisons with the Trevandrum Observatory, viz. on the 

 17th and 27th ; and the deduced error for the middle of the interval (the 22nd) can- 

 not be far from the truth. Mr. Newas's observation, which agrees with it within 

 about a minute, depends wholly on the observation for the sunrise ; it is so far con- 

 firmatory. Rejecting Capt. Carr's observation, as differing too much from the others, 

 the mean of the remaining three is 4 b 18J m . 



If we suppose the shock to have travelled in the direction from Quilou to Trevan- 



h m 



Mrs. Wilkins 4 19 



The mean gives 4 l6i 



