250 Suggestions for the Observations of the Tides. [July 



For example, the time which it employs in passing along a certain 

 line of coast, or across a sea, or round an island, or up a bay. 



N. B.— The Tide wave is the elevation of the waters by which High 

 water is produced in many places at once. It is not observed as a vi- 

 sible wave, but is found by drawing a line upon the globe through all 

 the places at which it is high water at a certain moment. The rate and 

 direction of its travelling are known by comparing the position of such 

 lines at successive times. 



N. B.— The Rate at which the Tide wave Travels is quite distinct 

 from the rate at which the stream of ebb or flow runs. 



N. B.— Also the Direction in which the Tide wave travels is quite 

 distinct from the direction in which the Tide ebbs or flows. 



The most proper Observations for determining the rate and course of 

 the Tide wave are those of the Time of High water on the same day at 

 different points (not too near nor too remote) on a continued line of 

 coast or sea. 



This may often be done by a person residing in any country by 

 making enquiries of persons conversant with the coasts, or by direct- 

 ing corresponding observations to be made at different places for a 

 few days only. 



If the places differ much in longitude, this ought to be noted, that 

 allowance may be made for the difference of the absolute Time of 

 noon. 



If there be any uncertainty as to the rate and course of travelling of 

 the Tide between two places, the doubt may best be removed by obtain- 

 ing Observations at some intermediate point or points. 



It is necessary to distinguish the Time of High water at the mouth of 

 a deep bay or sound, from the Time of High water further in. The 

 former is to be taken in all such comparisons as are here spoken of. 



Large islands and long promontories much disturb the regular pro- 

 gress of the Tide wave. 



Comparative Observations of the Height at different places in the 

 same seas, especially if combined with those of the Times, may also be 

 of great value. 



All communications concerning any Observations of the above kinds 

 made or to be made in any part of the world will be thankfully receiv- 

 ed. They may be addressed to the care of the Sec. Asiatic Societies 

 of Calcutta or Madras or direct to 

 The Rev. W. Whewell, Trinity College, Cambridge; 



or, at the Royal Society, London; 

 or the Astronomical Society, London." 



