Harmonic Analysis of Tidal Observations. 557 



Mr. J.N. Shoolbred, the Secretary of both Committees, was instructed 

 to intrust the curves to me, in order that they might be submitted to 

 harmonic analysis. He afterwards was so good as to obtain from 

 Mr. Druce the continuation of the Dover curves. As the reduction 

 of the whole series of curves would have been very expensive, it was 

 determined that only the curves for 1883-4-5 should be treated ; these 

 years were selected because there was reason to suppose that the 

 curves were more accurate than the earlier ones. 



To meet the expense of the reduction, Sir William Thomson obtained 

 50 from the Royal Society Grant, and this sum was afterwards 

 handed to me. The amount would, however, have been pjtogether 

 insufficient if Major Baird had not interested himself in the matter, 

 and introduced me to Mr. E. Connor, of the Tidal Department of the 

 Survey of India. Mr. Connor then generously offered to devote his 

 spare time to the work, and undertook the superintendence of the 

 native computers at Poona. The reductions of three years of Dover 

 curves, and of the same three of Ostend curves, have been made with 

 all the thoroughness and care of the Indian work. The computations 

 themselves are now in my hands, arid the curves have been returned 

 to Mr. Shoolbred. 



The tidal record was frequently interrupted at Dover, for there are 

 34 days wanting in 1883, 57 days in 1884, and 72 days in 1885. The 

 gaps are only of a few days at a time, except from September 24 to 

 October 26, 1885. 



The zero of the Dover gauge is said to be 8'67 feet below the 

 Ordnance datum, and therefore 1133 feet above the "international 

 datum," which is stated in the British Association Report (1879) on 

 Levels to be 20'00 feet below English Ordnance datum. 



The reduction of the tide curves shows that the mean sea level at 

 Dover was, in 1883, 0'52 foot; in 1884, 0'46 foot; and in 1885, 

 0'21 foot above Ordnance datum. 



The French JSTivellement General is 2'625 feet below Atlantic 

 M.S.L., and 1*992 foot below Ordnance datum. Hence Atlantic 

 M.S.L. is 0-633 foot above Ordnance datum. Thus Dover M.S.L. 

 was, in 1883, O'll foot ; in 1884, 0'17 foot ; and in 1885, 0'42 foot below 

 Atlantic M.S.L. 



It appears from the Ostend curves that Ostend M.S.L. was, in 1883, 

 0-25 foot ; in 1884, 0'37 foot ; and in 1885, (V21 foot above Ordnance 

 datum, and therefore in 1883, 0'38 foot ; in 1884, 0'26foot; and in 

 1885, 0-42 foot below Atlantic M.S.L. Thus Ostend M.S.L. was 

 below Dover M.S.L. by 0'27 foot in 1883 ; by 0'09 foot in 1884; and 

 they were the same in 1885. By reference to the Atlantic M.S.L. we 

 see that by far the larger part of these remarkable oscillations depends 

 on Dover. 



But it is nearly incredible that the sea at Dover should have been 



