At the meeting of the Quest Society Dr. Chatley spoke on the above subject. He commenced by describing in general terms the instruments which are used for observing the tremors of the earth's surface. The use of horizontal and inverted pendulums was referred to as an improvement on the older methods which employed vertical cylinders or balls in cups and some: details were gi of the very delicate Galitzin seismographs which are the last word in seismographic instruments. Reference was also made to the statistical and topographical study of shocks perceptible to all and to the general association of earthquake regions with fault lines, ocean abysses and volcanoes.
He went on to speak of the results of the analysis of the instrumental records, pointing out how comparison of the records at various stations of any one shock of known location enables the speed with which the tremor is transmitted to be calculated. The secondary waves due to direct transmission through the body of the earth and by reflexion from various parts of its surface indicate certain definite ideas the rigidity of the interior of the earth and provide a' means by which the position of a shock can be computed from instrumenta} records at a distant place. A study of the numerical frequency and relative magnitude of the shocks also serves as a rough guide to the future probabilities of quakes in any one locality.
Dealing with the cause of earthquakes he pointed out that the layers or strata of rock of which the surface of the earth is composed show cracks at various places which may -extend for many miles and along these cracks the rocks show clear signs of having moved. Such a crack is termed a "fault-line". and zones of great earthquake activity tend to lie on or near important fault lines. The varying thickness of the crust of the earth, as distinguished from the plastic "naga" beneath, is also a factor and it appears certain that the places where the surface slopes rapidly (as in the Tuscarora Deep east of Japan) are points of weakness. The continuous process by which rivers carve away the hills and deposit the material as silt or mud in the sea is one of the main factors in disturbing the balance of the crust; in addition to this there may be heat effects.
The mental effects of earthquakes are very important; in view of. the regularity and lack of discrimination shown by quakes they cannot be regarded as the "Decree of Heaven" in the Chinese moral sense, but there is still a wide belief in their retributive character.
Text read from the printed page and cleaned; old type leaves the occasional error.