216 BEPOBT — 1893. 



an instrument was described which gave a continuous record of tremors 

 and deflections of the vertical, and reference was made to earth-waves 

 which had a period of from fifteen to sixty minutes. The Reports for 

 1887 and 1888 formulated certain laws respecting the occurrence of earth 

 tremors or pulsations. Full accounts of all this work have been published 

 in the ' Transactions of the Seismological Society.' Last year I described 

 to this Association a method for the investigation of earth-pulsations and 

 earth-tilting, which consisted in making a continuous photographic i-ecord 

 of the spots of light reflected from mirrors carried by two horizontal 

 pendulums. These pendulums, which swing in planes at right angles to 

 each other, are each made from a piece of aluminium wire, 60 mm. in 

 length, tipped with a needle point resting in an agate cup. This is held 

 in a horizontal position by means of a quartz fibre. When adjusted so 

 that the period of swing is from five to six seconds, I find that a deflection 

 of the spot of hght upon the recording film of 1 mm. with one instrument 

 corresponds to a tilting of 0"54<", and with the other instrument of 0'68". 

 The distance of the lamp and film from the mirrors, which are arranged 

 to swing one above the other, is 3 feet. 



When describing this instrument iu 1892 I referred to it as being 

 new. In this I was mistaken, as similar arrangements have been used in 

 Potsdam and other places by Dr. E. von Rebeur-Paschwitz (see ' Der, 

 Ksl. Leop. -Carol. Deutschen Akademie der Naturforscher,' Band LX. 

 No. 1). In Japan the primary object of the observations was to obtain 

 continuous records of earth-waves (tremors), with the result that with 

 these records the records of other phenomena like those of earth-tilting 

 were found. In Potsdam the cycle of observations was reversed, the 

 primary object being to record small changes in the vertical, with the 

 unavoidable result that distant earthquakes, tremors, and other phenomena 

 were also recorded. 



The pendulums I have used have been exceedingly light, and intended 

 to follow the movements impressed upon them by a succession of earth- 

 waves. 



The pendulums of Dr. von Rebeur-Paschwitz were comparatively heavy, 

 and were adjusted to move with periods of from twelve to eighteen 

 seconds. 



The results obtained in December and January last are described in 

 detail in the ' Seismological Journal,' whilst that which has been done 

 between February and April is briefly as follows : — 



Daily Tilting. 



Almost every day the records show that the spots of light have been 

 displaced in a direction which would correspond with a displacement 

 should the N.E. or N.N.E. side of the column on which the pendulums 

 stand be gently raised, and then gently but rather more quickly lowered. 

 Occasionally the tilting is from the north, the pendulum in the meridian 

 which records the east and west motion remaining stationary. 



The movement commences about 7 p.m., and continues steadily up to 

 about 7 or 8 a.m. From this to about 10 a.m. there is a quick return 

 to the normal position, where it remains until evening. The amount of 

 tilting which would produce these deflections is from 2" to 10". The 

 average, as shown in the diagram, is about 4". 



