214 REPORT— 1887. 



Since 1883 several improvements have been introduced into the Gray- 

 Milne seismograph, and the instruments embodying these improvements 

 are now being manufactured by Mr. James White, of Glasgow. In the 

 original form of the instrument, as with all instruments with which we 

 are acquainted, after the occurrence of an earthquake the instrument 

 required to be provided with a new recording surface and reset. Unless 

 this was done successive earthquake-diagrams would be superimposed 

 upon each other, and even a single earthquake, if its duration exceeded 

 forty-five or sixty seconds, had the diagram of its later movements super- 

 imposed upon its first ; a method of recording which often resulted in con- 

 fusion. Further, the diagrams were written upon a surface of smoked 

 paper or smoked glass to preserve which varnishing was a necessity. In 

 the new form of instrument the horizontal and vertical motions are 

 written in ink, side by side, upon a straight baud of paper. Ordinarily 

 this band of paper is moving very slowly beneath the syphon pointers of 

 the seismograph. At the time of an earthquake the speed of the paper is 

 automatically increased for a definite period, after which it is automati- 

 cally slowed down to its ordinary rate. In this way earthquake after 

 earthquake may be recorded without the intervention of the observer, 

 whose only duty is to see that the instrument is supplied with paper and 

 the clockwork wound. A separate clock, arranged to keep accurate time, 

 impresses a mark on the paper ribbon every five minutes, and during 

 an earthquake every second. This improved seismograph is fully described 

 by Mr. Thomas Gray, who has taken great pains to perfect the apparatus, 

 in the ' Philosophical Magazine ' for April 1887. 



The importance of the instrument in its present form for the investi- 

 gation of special seismological problems — such, for instance, as the relation 

 of the 'Uri Kaishi,' or ' return shake,' which apparently succeeds all large 

 distui'bances to the disturbances which precede them — is evident to all 

 who have given attention to earthquake investigation. 



Remarks on the Earthquahes of 1886-87. 



From the preceding list it will be seen that between the end of May 

 1886 and May 1887 seventy-four earthquakes were recorded at the 

 Meteorological Observatory in Tokio. On the low ground in the same 

 city it is probable that a slightly greater number were sensible, and in 

 Yokohama, sixteen miles distant, which appears to be nearer to the origin 

 of many of the earthquakes felt in Tokio, the number may have been still 

 greater. During the two preceding years the number of disturbances 

 recorded in Tokio were respectively seventy-three and fifty-six. 



In 1886, as recorded by the 600 post-card stations distributed through 

 the empire, 472 earthquakes were felt, and for each of them the Earth- 

 quake Bureau, which is a branch of the Meteorological Department, has 

 drawn a map. I trust that at a future date I may be enabled to give the 

 British Association an epitome of the results obtained from these obser- 

 vations, similar to that which I had the honour of presenting in 1886. 



In looking at the catalogue published in this report, and also at the 

 catalogue iu the report for 1886, it will be noticed that there are several 

 records of vertical motion, which is a component of earthquake movement 

 about which we as yet know but very little, Frora these records it 

 appears that the vertical motion relatively to the horizontal is very quick, 

 so that two or three vertical movements are superimposed as ripples on a 

 horizontal wave. Professor K. Sekiya, in a model made of bent wire 



