25G ' EEPORT— 1808. 



Beitisii Assoctation for the Advancement of Science : 



Burlington House, 



London, W. 



Sir, — It is, I think, remarkable that there appears to be no publica- 

 tion which shows the corresponding value in Greenwich mean time of 

 the local time employed throughout the world. 



Such a table is indispensable in order to determine accurately the 

 instant of occurrence of earthquakes, sea waves, magnetic phenomena, the 

 despatch of telegrams, and many other events, the sequence of which in 

 absolute time has to be determined. 



Although application has been made to the Eoyal Observatory at 

 Greenwich, to the Royal Geographical Society, to the Central Telegraph 

 Office in London, to the offices of cable companies, and to other possible 

 sources of information, very little has been obtained. 



As a Secretary of the British Association Committee whose names 

 are appended, T desire to publish in their forthcoming Report a table 

 showing the differences between Greenwich mean time as used in England 

 and Scotland and that of the civil times used in various parts of the 

 world. 



By civil time I mean the time used by railways, telegraphs, and for 

 ordinary public affairs. 



If different times are used in various parts of your country, 1 trust 

 that you will be able to give information relating to the same. 



Feeling assured of the value of the table it is intended to compile, I 

 sincerely trust that you will favour me with a full and explicit statement 

 of the time generally employed in your country. If it is mean time, state 

 the meridian ; the observatory, or the place to which this refers ; and 

 also, as a check against any misunderstanding, please state distinctly the 

 equivalent of December 1, 9 a.m. G.M.T. in the local time, or times adopted 

 in your own country. 



I have the honour to remain, Sir, 



Your obedient servant, 



John Milne. 



X. Great Circle Distances and Chords of the Earth} 



The highest velocity which can be calculated for the transmission of 

 an earthquake wave is that which is determined when we assume that its 

 path from its origiti to an observing station has followed a great circle over 

 the surface of the earth, whilst a lower velocity is obtained on the hypo- 

 thesis that the movement has passed along a chord through the earth. 



Inasmuch as an earthquake origin, especially if submarine, cannot be I 

 determined with any degree of accuracy, whilst the origin itself may have 

 dimensions measured by several tens of miles, a simple and sufficiently 

 accurate method of determining great circle distances is to measure the 

 same with a flat steel tape or a piece of thread upon the surface of a | 

 globe. 



' A table giving the lengths in kilometres of .iics and chords of the earth has been ' 

 drawn up by Mr. James Arnott, and the same may be had on application to Mr. J.j 

 Milne, a secretary of this committee. 



