ON THE EARTHQUAKE AND VOLCANIC PHENOMENA OF JAPAN. 107 



disturbance which gaA^e them birth. If this is not done, then a large 

 disturbance which took place, for example, near the end of the winter 

 months may have the long series of shocks which follow, and which indi- 

 cate that the conditions which lead to earthquakes are being destroyed, 

 added in with the summer disturbances, and the rule that earthquakes 

 are more frequent in winter is obliterated. An effect of this description 

 is shown in the tables for 1889, which might have been drawn up omit- 

 ting 281 secondary disturbances which occurred in Hiogo. In connection 

 with these analyses it would .=!eem desirable that earthquakes should be 

 grouped according to their origins, and, in addition to what is done at 

 present, separate analyses be made for each group. Some of the earth- 

 quakes which occur in the north of Japan do not appear to have any 

 more connection with those which occur in the south of Japan than the 

 earthquakes of Great Britain have with the earthquakes of Switzerland. 

 The earthquakes from all these regions may conform with the law of 

 winter frequency, but it is also desirable to know the relationship between 

 earthquakes of a given group. Do the earthquakes which originate 

 beneath the ocean follow the same laws as those which originate in our 

 mountains ? Is the occurrence of earthquakes at one particular origin 

 more in accordance with some rule than the occurrence of similar dis- 

 turbances at some other focus ? With the aid of the four or five thousand 

 maps showing the area shaken by every earthquake since 1885 such 

 questions might be answered, but time and means for their analysis are 

 thus far wanting. 



On a New Method which may be Employed foe Investigating Earth 



Tremors or Earth Tips. 



In Reports to this Association in 1887 and 1888 I gave an epitome 

 of the work which had been accomplished in investigating small earth 

 movements called earth tremors. The more important results were, 

 that tremors were most frequent with a low barometer, and they were 

 especially noticeable if there was a steep barometric gradient. They 

 often occuri'ed when it was absolutely calm in Tokio, and often heralded 

 the approach of a wind from the south-west. The instrument employed 

 was automatic in its action, the records being made at intervals of five 

 minutes. Being, like all other tromometers, of the ordinary pendulum 

 type, it only indicated when tremors were strong and the time of their 

 occurrence. The instruments which I have been using for the last few 

 months give perfectly continuous records of earth tremors, measure them 

 as to amount and direction, and throw considei-able light upon the nature 

 of these movements. From the character of the records it is also seen 

 whether the column on which ihe instruments are placed remains 

 horizontal or suffers tilting. Anyone possessing a small metal stand 

 which has three levelling screws and a metal upright can, with a silk 

 fibre, a small sewing-needle, a small shot, and a glass fibre, construct one 

 of these instruments. In the sketch, a h represents the needle, with the 

 shot fixed at a, and a c the fibre, which is secured at a and c by shellac. 

 The glass fibre is joined to 6 a as a continuation of its length. This acts 

 as a pointer, and moves above a mirror, on which there is a finelj'- divided 

 scale. The fibre may be replaced by a rigid wire, when it must be properly 

 pivoted. Agate cups at b and c give greater sensibility. A complete- 



