72 report— 1879. 



direction of Mr. Edward Druce, C.E., the resident engineer in charge of 

 the Admiralty Works at Dover. It will remain, of course, in the hands 

 of, and under the control of the Board of Trade. 



The Committee having secured for the simultaneous tidal observa- 

 tions in the English Channel and in the Irish Sea, their main duty, the 

 hearty co-operation of the Admiralty, of the Board of Trade, of the 

 French Minister of Public Works, as well as of the Minister of the same 

 department in Belgium, and also of a number of private observers, both 

 in this country and on the Continent, a programme of observations at 

 different times during the spring and summer of 1878 was arranged, in 

 accord with the different observers, a copy of which will be found in 

 Appendix I. These simultaneous observations extended on the English 

 side of the Channel from Portland to Yarmouth, while on the Continent 

 they embraced the coast from Havre to the mouth of the North Sea 

 Canal, leading up to Amsterdam. 



Comparative tables are given in Appendix II., which show the 

 times and the levels of the high waters and of the low waters at the 

 different places, during the equinoctial tides observed in the month of 

 March ; which may be taken as typical of the two other months. They 

 are all reduced to Greenwich time and to the level of twenty feet below 

 the Ordnance datum of Great Britain. This is in accordance with the 

 suggestion of the Committee on the Ordnance datum of Great Britain. 1 

 The level proposed as a datum of comparison for tidal observations of 

 an international character, viz., ' 20 feet below the Ordnance datum of 

 Great Britain,' is a point which practically coincides with ' 5'50 metres 

 below the French Zero du Nivellement ' (Bourdaloue), and with ' 12 

 feet 6 inches below the Ordnance datum of Ireland.' Some of the tidal 

 curves from different points of observation are also appended ; several 

 distinctive peculiarities, such as double tides, &c, are exhibited in them. 

 See Plates. 



A careful consideration of the observations shows that on one point 

 alone, that of tidal constants, much valuable information might be added 

 to that already available, if a series of simultaneous observations, of a 

 somewhat similar character to those just obtained, were carried out 

 uninterruptedly, over a considerable period, of not less than twelve 

 months, and over a large extent of coast. The Committee, however, 

 feel that such a duty hardly falls within their province. They beg to 

 suggest that, possibly at some future time, this subject might be 

 entrusted to some suitable body; the more so, that the basis of the 

 means of obtaining the necessary observations is already furnished by 

 the labours of this Committee, with a considerable extension, however, in 

 the number of points of observation. 



Before concluding their labours, the Committee request that the 

 thanks of the British Association be conveyed to the First Lord of the 

 Admiralty, the President of the Board of Trade, the French Minister of 

 Public Works, the Belgian Minister of Public Works, and to the several 

 other authorities and private individuals, both in this country and on the 

 Continent, who have kindly and gratuitously had the various observations 

 carried out and communicated to this Committee ; and more especially 

 would they beg to thank the French Association for the Advancement of 

 Science for its cordial assistance in supporting the proposal of the British 



1 See p. 219 of the present volume. 



