276 



MR. LUBBOCK ON TIDE OBSERVATIONS. 



or those which have reference to the height of high water ; but the equation of time 

 is mixed up with the changes in the interval between the moon's transit and the 

 time of high water due to changes in the moon's declination ; and any uncertainty 

 with respect to the manner in which the clock has been regulated is therefore much 

 to be regretted. 



The plan pursued is the same as that which I adopted with respect to the London 

 Dock observations, and which seems to me to be the only one, in the present state of 

 the subject, which can be resorted to with advantage. If the theory were complete, 

 and the laws or analytical expressions of the phenomena had been made out satisfac- 

 torily, it would be possible to proceed at once to determine the constants, which might 

 be done by means of fewer observations, and those might be selected which appeared 

 entitled to the greatest confidence : at present, however, I do not think that this 

 course can be safely pursued. 



I trust that this laborious work, which M. Dessiou has accomplished at my insti- 

 gation, and by the liberal support of the British Association, will not be without uti- 

 lity, and will afford data upon which mathematicians who may hereafter improve 

 the theory of the tides may safely rest their conclusions. 



The tides in this port continue to be observed at the London and St. Katherine 

 Docks. These Docks are contiguous, so that the places at which the observations 

 are made are not distant from each other more than 900 yards, as appears from the 

 diagram underneath. 



/ 



500 



River Thames 



Scale of Feet. 

 1000 1500 



2000 



2500 



We may therefore, I think, safely conclude, that whatever cause affects the tide at 

 one place will equally affect it at the other ; and hence, if we find the difference 

 in the registers of the times and heights of high water much greater than the average 

 difference, suspicion arises that the observation at one or the other place must be 

 erroneous. The observations at the London Docks are made (at the place of the 

 letter d) by a person who notes the time when the water has begun to fall, that is, 

 has made its mark. Those at the St. Katherine Docks are made by noting upon a 

 slate (ruled for the purpose) the height of the water every minute for a short time 



