MR MILNE ON A REMARKABLE OSCILLATION OF THE SEA. 635 



" Mr WALKER has observed, with respect to the influence of the pressure of 

 the atmosphere upon the tidal waters on the shores of Cornwall and Devon, that 

 a fall of 1 inch of the mercury in the barometer, corresponds with a rise of 16 

 inches in the level of the sea, more than would otherwise happen at the same 

 tune, under the other general conditions ; a rise in the barometer of 1 inch 

 marking a corresponding fall in the sea-level of 16 inches. This he found to 

 be the usual rate of such alterations in level ; but very sudden changes in the 

 pressure of the atmosphere are accompanied by elevations and depressions equal 

 to 20 inches of sea- water for 1 inch of mercury in the barometer. Regarding the 

 whole pressure of the atmosphere over the globe as a constant quantity, all local 

 changes in its weight, merely transfer a part of the whole pressure from one place 

 to another ; and hence he concludes, that the subjacent water only flows into, or 

 is displaced from, those areas, where, for the time, the atmospheric pressure is 

 either less or greater than its mean state, in accordance with the laws which 

 would govern the condition of two fluids situated in the manner of the atmo- 

 sphere and sea. We might account for the difference observed by Mr WALKER, 

 in the amount of depression or elevation of sea-level produced by sudden changes 

 in atmospheric pressure, by considering that a sudden impulse given to the par- 

 ticles of water, either by suddenly increased or diminished weight in the atmo- 

 sphere, would cause a perpendicular rise or fall in the manner of a wave, beyond 

 the height or depth strictly due to the mere change of weight itself." l 



These inferences of Mr WALKER'S have been confirmed by observations made 

 by Mr LUBBOCK at Liverpool, and by Mr BUNT at Bristol. Mr LUBBOCK calculated 

 the amount of rise in the sea level, for a depression of one inch of the barometer, 

 to be 11.2 inches; 2 Mr BUNT calculated it to be 15 inches. 3 This last is pro- 



1 " A circumstance connected with this subject, of considerable practical value, has been noticed by 

 Mr WALKER during his long-continued observations. He has found that changes in the height of the 

 water's surface, resulting from changes in the pressure of the atmosphere, are often noticed on a good 

 tide-gauge before the barometer gives notice of any change. Perhaps something may be due in these 

 cases observed by Mr WALKER to the friction of the mercury in the barometer-tube, as it is well known 

 that in taking careful barometrical observations it is necessary to tap the instrument frequently and 

 carefully, to obtain the measure of the true weight of the atmosphere at a given time and place. The 

 practical value of the observation is, however, not the less, be the cause of the phenomenon what it may ; 

 for if tide-gauges at important dock-yards shew that a sudden change of sea-level has taken place, indi- 

 cative of suddenly-decreased atmospheric weight, before the barometer has given notice of the same 

 change, all that time which elapses between the notices given by the tide-gauge and barometer is so 

 much gained ; and those engaged with shipping know the value of even a few minutes before the burst 

 of an approaching hurricane." (Note by Sir HENRY DE LA BECHE on the page above referred to.) This 

 passage affords a confirmation of the view above suggested, that a diminution of atmospheric weight will, 

 in certain cases, be indicated by an oscillation of the sea before it is indicated by a fall of the barometer, 

 or a change in the state of the weather. 



2 Transactions of Royal Society of London for 1837, p. 103.. 



3 British Association Reports for 1840* p. 30. 



