Breaks in Tide Curves from Recording Gauges 



77 



enable a good interpolation to be made; or on the other, when a large 

 difference in the height of high and low water on the two curves of the 

 pair, made the interpolation uncertain within appreciable limits. This 

 difficulty only occured during one half of the day, however, when the 

 diurnal inequality was large owing to the moon being in high declination 

 at that point in the month. At such times it could not be assumed that 

 a curve exactly midway between the pair, whether in time or in height, 

 would be truly correct in position. 



It was evident therefore, that if this compromise interval between the 

 lengths of the months is to be adopted as a basis of interpolation, some 

 method of checking the position of the intefoplated curves at the points 

 of high and low water should also be devised. As a rule, it is only 

 necessary as above pointed out, to obtain the co-ordinates of the Higher 

 high water and the Lower low water of the day. The method of com- 

 putation is on exactly the same system as the double interpolation 

 already described; as will be seen in the table here given. The interval 

 of 28 >2 days is the actual mean between the periods of the Synodic and 

 Declinational months. It is also to be noted that the computation is 

 based entirely on values read from the recorded curves, and not on pre- 

 diction values from the Tide Tables. 



The degree of accuracy of this computation may be tested by the 

 method shown in the first of the tables appended, in which the Synodic 



