APPENDIX. 91 



which the shock travels are useless ; general impressions of the nature of the shock 

 should be carefully noticed, as also any effects it may have on the lower animals. 



The time at which the shock is felt should, of course, he noted ; but this, which in 

 India it is impossible to expect done with accuracy, is fortunately of comparatively 

 small importance, its purpose being mainly to obtain the rate of transmission of the 

 wave impulse through various media ; but, though the actual time at which the 

 principal shock is felt may not be determinable with accuracy, the intervals between a 

 great shock and the numerous minor ones which follow it should, if possible, be 

 determined with rigorous accuracy. And here we may diverge to say that it is not by 

 any means the great and disastrous shocks which are of greatest scientific interest ; in 

 them the chief wave is so interfered with by minor cross undulations that the general 

 motion, instead of being simple, is much complicated. Let every fact that can be ascer- 

 tained about such a shock be recorded, but let it be taken rather as a warning to be on the 

 alert and notice any following shocks, to read off the instruments and set them again 

 ready for the next shock, than as the main point to which observation should be directed. 

 The duration of the shock should be noticed ; this, as given in most ordinary 

 accounts, is very misleading : for instance, the shock may be said to have lasted for 

 ' several minutes' or ' quarter of an hour/ whereas what is really meant is, that during 

 that period there was a rapid succession of shocks. If possible, in the case of a violent 

 earthquake, the main wave should be distinguished from the accompanying minor 

 undulations, and it should be noticed to what extent the latter precede or follow it. 



The nature of any sounds heard should be recorded, and whether they accompanied, 

 preceded, or followed the shock. 



It is but seldom that any of the Indian earthquakes originate under the sea, and 

 consequently sea-waves are seldom found accompanying earthquakes ; but in the case of 

 observers residing near the seashore, any such phenomenon should be carefully recorded. 



Often chandeliers, trees, or other flexible objects are set swinging by the shock, 

 in which case the direction of movement, with reference to external objects, should be 

 noticed, and the actual direction of this motion afterwards observed with the compass. 

 Among those observations which should be made after the passage of the shock, 

 the principal are those of damage done to buildings. These should in every case be 

 carefully observed, and drawings should be made of the faces of the building cracked, 

 and particulars given of size and construction, thickness of walls, number and size 

 of doorways and other openings. From these particulars valuable information may 

 often be derived ; but as a rule little can be expected, unless the observer is acquainted 

 with the principles on which these facts are interpreted. Should, however, any walls or 

 other structures be overthrown, they should be most carefully described. A rough, or, 

 if possible, a detailed ground plan of the overthrown structure should be made, 

 accompanied by drawings and a description of the structure as it originally stood. The 

 direction in which the mass is overthrown should be carefully recorded ; in the case 

 of bodies projected by the shock their dimensions and nature should be detailed, and 



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