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need be said. It is admitted by the best authorities that we 

 know but little of the condition of the interior of the earth, 

 or how the forces with which we are familiar at the surface, 

 act within the earth so as to produce earthquake and volcanic 

 phenomena. 



We know that many, perhaps most, rocks even near the 

 surface, are in a state of strain, and that if at any time they 

 yield to this strain a vibration will result which will be propa- 

 gated through the earth as a tremor or shock. We know 

 also that at a short distance from the surface of the earth in 

 most parts of the world a very high temperature prevails. 

 Also that water is present in most rocks, and that either in 

 the liquid or gaseous state it appears to play a great part in 

 all volcanic eruptions, and to have been present during the 

 formation of most granite and other crystalline rocks. But 

 when we have said this we have to admit that almost all the 

 rest is still in the region of theory or hypothesis. 



Of course it is easy to shew that, if the temperature goes on 

 increasing at the rate of about 1° F. for 65ft. of deptli, as it does 

 near the surface, we should have at a depth of a few miles an 

 enormous heat. But then we are not sure that it does go on 

 thus increasing, and even if it does we don't know the 

 materials which exist within the earth, or how thew would 

 Dehave at temperatures, and under pressure of which we have 

 no experience at the surface. It is tolera^bly clear also that 

 volcanoes are allied to severe earthquakes, but whether all 

 earthquakes are due to similar causes is not so clear. 



We" know that vast masses of molten rocks must exist 

 within the earth in some places and at some times, since they 

 are poured out at the surface, but we are not, therefore, 

 justified in assuming that the whole interior of the earth is 

 liquid. 



Under these circumstances it is far better for those who 

 desire to advance the cause of science to confine themselves 

 to observing rather than to propounding theories. 



From what has been said it will be seen the directions in 

 which observations of earthquake phenomena are wanted, 

 and any intelligent person may be placed in a position where 

 careful and judicious observation will lead to valuable re- 

 sults. The time of shocks should be noted with especial 

 care, and if an observer is not sure of the exact time, that 

 should be stated, so that it may be tabulated accordingly. 

 Again, some rough form of seismometer may be devised to 

 determine approximately the direction of the wave. A basin 

 of mercury or treacle, a few pieces of wood, or similar 

 arrangement may furnish a good result if carefully attended 

 to, as an elaborate seismograph or seismometer which may 

 be out of order at the very time it is wanted. If clocks are 



