306, ME. H. G. MADAN OS AN EBBING AND [Aug. 1 898,: 



of greater density (optically speaking), the velocity (though not the 

 frequency) of the wave is lessened, and it takes a longer time to 

 reach a given point in the denser medium than it would have done^ 

 if its course had been continued in the rarer medium. 



Postscript. 



[Analysis or the water of the tidal well at TsTewton Nottage,. 

 made about the year 1889 by Dr. Voelcker, for the special purpose 

 of ascertaining its quality as a water for drinking purposes. 



(The results are expressed in grains per gallon, or parts in 70,000.) 



Total solid residue 60-48 



Oxidizable organic matter 0"15 



Chlorine 15-98 



(Equal to chloride of sodium 26"35) 



Nitric acid, as nitrates ■ 2*62 



Hardness, according to Clark's scale 26 "4° 



The water also contained, 



Free ammonia 0*0005 



Albuminoid ammonia... 0025 



The foregoing analysis is inserted by kind permission of Mr. Knox.. 

 —May 31st, 1898.] 



DiSCDSSION. 



Mr. J. G. Wood considered that the observations, valuable so far 

 as they went, required to be continued, over a more extended 

 period and under more varying conditions of tide, before any definite 

 conclusion could be arrived at. The diagram assumed an uniform 

 interval of 12 hours between low water and low water. This 

 would be nearly correct at spring tides, but much too short at 

 neap tides. Again, the rise and fall at spring tides would be about 

 20 feet more than at neap tides. It was essential to correlate all 

 such variations of tide with the fluctuations of the well. 



As another instance of fresh water fluctuatiug inversely with the 

 tide, the speaker referred to the wells at Perim described by 

 Mr. Moore in the Woolhope Club Transactions for 1892 ; and he 

 also mentioned a well at Chepstow, described by himself in the 

 same volume, which was commonly said to ebb and flow in like 

 manner. In fact it does not ebb, but can be pumped dry, and will 

 remain dry while the tide is in. The increase of pressure on a 

 fault which fed the well was the probable cause of its temporary 

 failure. Similar causes might possibly be at work at Newton 

 Nottage, owing to the complications of the strata in the district. 



Dr. Churchward asked whether there was any iodine or bromine 

 found on analysis of the water. He also wished to know the 

 depth from which the samples of the water were taken in the well. 

 One would consider this of some importance, as tendins: to show 

 whether the sea- water had percolated or difi'used through the fresh 



