RECOMMSNDATIONS. 485 



The direction of the wind, and the height of the barometer 

 and thermometer. 



The direction and velocity of the stream of flow and ebb. 

 At what hour (with respect to the time of high water and 

 low water) the slack water after the stream of flood, and after 

 the stream of ebb, respectively occur. 



The height of the water must be given from some fixed mark 

 or line, which should be described accurately, so that it may 

 be easily found again at a future time. The observer ought to 

 state the manner in which the height was measured ; the man- 

 ner in which the moment of high water was fixed upon ; the 

 time employed, tohether apparent or mean solar time, and how 

 it was obtained. 



The height of the water at the end of every minute, for 

 half an hour before the expected time of high water, and until 

 there can be no doubt that the time of high water is past. 

 Machines to dispense with this minute attention are described 

 in the Philosophical Transactions, 1831, and in the Nautical 

 Magazine for October 1832 ^ 



The uncertainty occasioned by waves may be avoided by 

 making the observation in a chamber, to which the water has 

 access by a small opening, or by fixing in the water an upright 

 tube, (of wood or iron, for instance,) the bottom or sides of the 

 tube being perforated ; in either case an upright measuring 

 rod, carefully graduated, and connected to a float, will rise and 

 fall with the tide, and permit, at any moment, the height of the 

 water to be read, ofi" against the collar through which it works. 

 This rod may be so constructed as to leave a moveable index 

 at the highest and lowest points. 



A long sei'ies of continued observations can alone be of use 

 towards the determination of the dependence of the time, 

 height, and other circumstances of high and low water upon 

 the places and distances of the sun and moon ; but a smaller 

 number of observations will often be sufficient to determine the 

 establishment of any place, with more or less accuracy, accord- 

 ing to the number of observations ; and the best mode of do- 

 ing this is by comparative observations with some place of 

 which the establishment is accurately known, or where obser- 

 vations are continually carried on. A few sets of comparative 

 observations of neighbouring places will give the relative time 

 of high water at these places with considerable accuracy ; and 

 thus the motion of the tide-wave and the arrangement of the 



1 Tide-guages may be seen in operation at St. Katharine's Docks, London. 

 An excellent one has lately been set up near Bristol by the Literary and Phi- 

 losophical Institution of that city. 



