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Published online by Cambridge University Press: 17 January 2013
This phenomenon presented a remarkable interference with those laws which govern the ordinary movements of the ocean. It occurred at one place whilst the tide was flowing, at another whilst it was ebbing; in some cases, producing a sudden retrocession of the waters,—and in others, as sudden an impulse of them on the shore.
The period during which the sea thus continued to retreat and rise respectively, was generally from ten to fifteen minutes. It then made a momentary halt—after which, it began to flow in the opposite direction, and which it continued to do, for about the same period which characterised its previous movement.
In this state of alternate flux and reflux, the sea was at most places observed to continue, for three or four hours together.
page 609 note 1 Edinburgh New Philosophical Journal for January 1844, p. 188.
page 610 note 1 The notices here given in regard to Mountsbay, are abbreviated from an account which appeared in the Literary Gazette of 15th July 1843.
page 612 note 1 I think that there is a mistake here for the 6th July, for on the 5th July it was low water at 10h 36′ A.M., and on the 6th July at 11h 41′ A.M.
page 612 note 2 For this report, and all the others from lighthouse-keepers, quoted in the subsequent parts of this paper, I am indebted to Mr Stevenson, the engineer of the Northern Light Commissioners. And I take this opportunity of acknowledging the readiness and liberality with which these authorities undertook to obtain for me returns from all the lighthouse-keepers under their superintendence.
page 616 note 1 Gentleman's Magazine.
page 617 note 1 London Philosophical Transactions, vol. xlix. p. 530.
page 617 note 2 Doddsley's Annual Register, vol. iv. p. 137; Gentleman's Magazine.
page 617 note 3 Doddsley's Annual Register, vol. vi. p. 99.
page 617 note 4 Doddsley's Annual Register, vol. iv. p. 142; Gentleman's Magazine; London Philosophical Transactions, vol. lii. p. 508.
page 617 note 5 London Philosophical Transactions, vol. iv. p. 83; Doddsley's Annual Register, vol. vii. p. 50.
page 618 note 1 Doddsley's Annual Register, vol. x. p. 126; Gentleman's Magazine; London Philosophical Transactions for 1768.
page 618 note 2 Doddsley's Annual Register, vol. ix. p. 67.
page 618 note 3 Ibid, vol. xiii, p. 99.
page 618 note 4 London Philosophical Transactions for 1771.
page 618 note 5 Doddsley, vol. xxxv. p. 32, and Gentleman's Magazine.
page 618 note 6 Gentleman's Magazine.
page 618 note 7 Climate of London, vol. i. Table 57.
page 619 noet 1 Doddsley, vol. liii. p. 62.
page 620 noet 1 Gentleman's Magazine.
page 621 note 1 Extracted from a Wexford paper.
page 629 note 1 Sir Thomas Brisbane informs me that his attempts on the 5th July to deduce the height of Mackerston above the sea, were completely frustrated, the three excellent barometers which he employed, having given very inconsistent results. He adds, “I have learnt an useful lesson—not to depend on Barometrical determinations when the atmosphere is disturbed by a thunder-storm.”
page 631 note 1 Bristol Mirror Newspaper, of 15th July 1843.
page 632 note 1 At Brighton, the 5th July was the warmest day of the summer, the thermometer having stood at 78° in the shade. But at night it sunk down to 55½°.
page 633 note 1 There is some doubt as to this. In the Athenæum of 1843, p. 849, it is stated that the tide had ebbed about half an hour when the oscillation occurred. Now, it was high water in Mountsbay at 9h 54′ A.M., and, according to this account, the oscillation occurred about 10h 24′.
page 634 note 1 Report on the Geology of Cornwall and Devon, p. 11.
page 635 note 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, indicative 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.
page 635 note 2 Transactions of Royal Society of London for 1837, p. 103.
page 635 note 3 British Association Reports for 1840, p. 30.
page 636 note 1 Robertson on the Atmosphere, vol. i. p. 105.