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[No date]
Dear Sir,―
It will be a great favour if you will send to the above address a copy of your Earthquake Register, commencing with the first of your records, or with the entry following the last of the series relating to your Station published in the British Association Report for 1899, and ending on December 31st of this year. This request is being forwarded to all Stations with similar instruments. The replies will it is hoped be printed and issued about the end of March, 1900.
To facilitate comparison between the various Registers, it is desirable that they be drawn up in tabular form, the headings to seven columns being as follows:
(1) Number. This is the number of the Earthquake in your Register.
(2) Date. Month and day.
(3) Commencement. This is the Greenwich Mean Civil Time of the first trace of motion, given in hours, minutes, and decimals of the same.
(4) D. first P.T’s. Or the duration of the first Preliminary Tremors. This refers to the first uniform thickening of the race or to the first phase of motion.
(5) Maxima. These entries refer to the times of the large movements, the principal of which will be recognized by its amplitude given in the next columns.
(6) Amplitude. To be stated in seconds of arc, and placed opposite to the times at which they were noted.
(7) Duration. Hours and minutes
At the end of the table, remarks may be given, each prefixed by a number corresponding to that of the Earthquake to which it refers.
On any important Seismogram which may be sent, it is necessary that at least one point in the same (the commencement or any well marked phase) should have the exact Greenwich Mean Civil Time of its occurrence indicated, and also (if the hour marks are not visible) there should be a statement of the exact number of milimetres equivalent to one hour.
Yours faithfully,
J. MILNE,
Hon. Sec. Seismological Investigation Committee,
British Association. |