ON THE DISCUSSION OF LEITH TIDE OBSERVATIONS. 33 



" The mean depression of tide corresponding to 1 inch rise of barometer, is 



inches. 



For 1834 13"4 (contemporaneous barometer), 



1835 14-6 ( ditto ditto ), 



1836 11-9 ( ditto ditto ). 



Mean. ... 13'3 for three years." 



Thus this last investigation appears to have put a negative upon the 

 supposition that the barometric correction of the height of high water cor- 

 responds to an anterior epoch ; for we cannot doubt the justice of the re- 

 mark made by Mr. Bunt, that since not only the contemporaneous barometer 

 gives the greatest result, but since also equal differences from the maximum 

 attend the epochs anterior and posterior by twenty-four hours, the contem- 

 poraneous epoch must be the true one. And thus it appears that the effect 

 of atmospheric pressure on the height of the tide is something local and im- 

 mediate, not an effect transmitted in a finite time from some other place. 



I next wished Mr. Bunt to try how far the correction curves of height for 

 lunar and solar parallax and declination would have been different if the 

 barometric correction had been m&die first, before the heights were arranged 

 for the other corrections. This also he undertook. The following is his 

 communication on the subject. 



"April, 1841. 



"I send you new correction curves made from the observed heights in 1839, 

 after haw'mg first cleared them of the effects of the changes of atmospheric 

 pressure, allowing 13^ inches of water to one inch difference in the barome- 

 tric column. The greatest difference is in the solar declination curve at the 

 hour 65 of transit. I hardly think this can be entirely owing to the atmo- 

 spheric correction, but most likely to some difference in the working out of 

 the new lunar corrections, especially that for declinations, with which the 

 solar declination is almost inseparably mixed up in any short series of obser- 

 vations. Indeed I can scarcely see how the effects of the two kinds of decli- 

 nation can be separated, with any certainty, about the hours of 0'' and Q^ 

 transit, except by taking two sets of observations, the one having the moon's 

 declination a maximum, and the other a minimum." 



The very small differences between these correction curves in their former 

 shape, and as modified by allowing for the barometric correction, might have 

 been expected, since the barometric correction will, on the whole, compen- 

 sate itself. The smallness of the differences is, however, evidence of the 

 care and consistency with which our results were formerly obtained. 



W. Whewell. 

 Trinity CoUege, Cambridge, July 1, 1841, 



Report on the Discussion of Leith Tide Observations, executed by Mr. 

 D. Ross, of the Hydrographer's Office, Admiralty, under the direc- 

 tion of the Rev. W. Whewell. 



Although tables of the corrections of the heights and time of high water, 

 due to lunar parallax and declination, have already been obtained for several 

 places, (London, Liverpool, Plymouth, and Bristol) it is still desirable to cor- 

 rect and confirm these results by the discussion of observations made at other 

 places, especially if continued for a considerable series of years. Our methods 

 of discussion and tabulation may admit of improvement, and new features 

 may appear in the new results ; with these views I applied at the last meeting 

 1811. D 



