ON THE EARTHQUAKE AND VOLCANIC PHENOMENA OF JAPAN. 139 



balanced on the extremities of beams carried upon knife edges. One box 

 had a bottom made of tin and the other of fine wire netting, and each was 

 filled with earth. Excepting when they were weighed, by placing weights 

 at the other ends of the beams, they Avere allowed to rest on the soft 

 earth of my garden. Sometimes it was found that during a night both 

 boxes would lose weight, but at other times it was found that the weight 

 of the box with the tin bottom had not changed, whilst the one with the 

 wire netting had gained from 2 to 2-5 ounces, which apparently showed 

 that there had been a condensation of moisture coming up frona beneath 

 of 10 ounces per square yard, or about one-eighth of that which might 

 have been removed during a day by evaporation. As my notes upon 

 these experiments were destroyed by fire, what is here said can only be 

 taken as indicating the character of a phenomenon which hitherto has not 

 received attention. 



Whether the causes which have been described are sufficient to account 

 for the diurnal movements of a horizontal pendulum remains for future 

 investigators to decide. 



The gradual taking away of weight, followed by a gradual addition of 

 weight unequally on the two sides of a pendulum during each period of 

 24 hours, will account for the observed movements, and iii the evapora- 

 tion of moisture during the day and the precipitation of moisture on 

 the surface, together with its condensation beneath the surface during the 

 night, we have phenomena which relieve or load surfaces in the required 

 manner. 



(h) Tremors. 



In the third Report to the British Association, 1883, after observing 

 tremors with the ordinary Italian form of tromometer, I attributed their 

 origin either to the effects of high winds or to small but rapidly recurring 

 variations in atmospheric pressure, such as may be observed during a 

 typhoon. 



After analysing a long series of records of these movements, which 

 were obtained from an automatic tremor recorder, and comparing the 

 results with observations made in Italy, the conclusion arrived at was that 

 tremors were at a maximum when the barometrical gradient was steep, 

 no matter whether at the place where the tremors were observed the 

 barometer was high or whether it was low. 



This relationship between tremors and the state of the barometric 

 gradient, although it did not explain the origin of tremors, tended to 

 destroy the distinction between tremors which occur with a low barometer, 

 and are called haro-seismic motions, and those which appear during periods 

 of high pressure, which are called volcano -seismic disturbances. 



An examination of the photograms obtained from the horizontal 

 pendulums, which permit of more accurate analysis than those previously 

 obtained, although it does not show that tremors only occur at the times 

 when the bai-ometric gradient is steep, shows that at such times tremor 

 storms are marked. These same diagrams, however, on account of the 

 relationship they show between tremors, the changes in the position of a 

 horizontal pendulum, barometrical pressure, and the diurnal wave, lead 

 me to withdraw the suggestion that, because steep gradients are usually 

 accompanied by wind, such winds, whether they are local or distant, may 

 be the immediate cause of tremors. In their times of occurrence winds 



