EARTHQUAKE PHENOMENA. 431 



or other mineral masses through which the speed of transit of the 

 earth- wave has has been carefully observed, as will enable the mean 

 modulus of elasticity of the mass to be determined. Where this is rock, 

 three specimens should be taken of maximum, minimum, and average 

 hardness, density, and compactness, as representatives of the whole, 

 noticing especially in stratified rock the depth from surface of ground 

 and from top of the formation at which taken; each specimen to be of 

 a size enabling a block to be sawn out of it of at least three feet in 

 length by four inches square. Where convenient, this operation may 

 be done on the spot. An iron wire stretched like a bowspring, with 

 some sharp sand and water, makes an excellent stone saw; still better 

 where continuous motion can be given by a band to the wire wheel 

 and winch handle. Where the district is a deep detrital or alluvial 

 one, the depth and characters of the loose materials should be care- 

 fully observed, and illustrative specimens, as far as possible, brought 

 home. It is in the highest decree important that the decree of shat- 

 teryness or compactness of the rock formations, the nature, directions, 

 closeness, or openness, and contiguity of the fissures be remarked, as 

 these conditions of comparative discontinuity most materially affect 

 the transit period of the shock in every formation. 



Collateral conditions to be observed are : Barometer before, during, 

 and after the earthquake; thermometer and rain gage; hygrometer 

 and electrical state of the air during the phenomena; magnetometrical 

 observations to be made where these are practicable; all unusual 

 meteorological appearances to be noted, and all changes or perturba- 

 tions of climate or season observable for a year before and after the 

 shock are desirable to be ascertained. Also, whether epidemic or other 

 diseases follow, and have a distinct connexion of cause and effect with 

 the earthquake, as by change of season, failure of crop or food, injury 

 to arterial drainage, the presence of fogs or exhalations, or like 

 events. 



The effects of the shock itself on man and the lower animals to bo 

 noticed. Nausea is undoubtedly a frequent effect upon human beings 

 at the instant of shock; but the nature of its production is uninvesti- 

 gated. Is it due to nervous perturbation, or to the movement, as in 

 the case of sea-sickness? Some animals appear to predict the shock 

 before men are conscious of its approach. Birds are often killed by 

 being throwm off their roosts while asleep at night. Flat fish on the 

 sea bottom are often killed by the direct blow of the steeply emer- 

 gent wave. All such modes of death should be noted. Active vol- 

 canic phenomena occurring before, during, or after the earthquake, 

 in adjacent or distant regions, will, of course, be recorded. 



Records or trustworthy traditions are to be sought for in new or little 

 explored volcanic countries, or those neighboring to them, as to the 

 state of activity or repose of these vents for a long period prior to 

 and during the earthquake; also as to their state before and during 

 any previous earthquakes — all remarkable facts as to which should be 

 collected. Where meteorological or tidal tables exist they should be 

 transcribed for the times correlative to the above records. The opinions 

 of old observers as to changes of climate or "season; the occurrence 



