Cambridge Philosophical Society. \i\ 



been discussed in former memoirs by the author, and its laws so 

 full}' made out, that this inequality has been introduced into the 

 tide tables for Liverpool and for Plymouth. This inequality depends 

 mainly on the moon's declination. In England it is small : it is very 

 marked on the coasts of Spain, Portugal and North America, as was 

 shown by the observations of 1836 : but in the North Pacific and 

 in the Indian seas, it reaches an enormous amount, and shows itself 

 with curious differences. In many places in those seas, the diurnal 

 inequality is much larger than the differences of spring and neap 

 tides, and is so large as utterly to confound the usual modes of 

 estimating the " establishment " of a place. 



This inequality affects the tides of various parts on the coast of 

 Australia to a very great amount, and with very remarkable differ- 

 ences. It is seen at Adelaide on the south, and Port Es-ington on 

 the north coast ; and at each place it produces a difference of several 

 feet between every two successive tides, when it is at its maximum : 

 but this difference affects mainly the high waters at Adelaide and the 

 low waters at Port Essington*. Also on the west coast of Australia, 

 near Swan River, the diurnal inequality appears with another pecu- 

 liarity, affecting the times of high water rather than the heights. 

 These differences, the author remarks, show that the diurnal wave 

 travels separately from the semidiurnal wave ; but our materials do 

 not at present enable us to analyse the compound tide into these 

 two waves, and to trace the course of each. 



The author observes, in conclusion, that our knowledge of the tides 

 is not likely to be completed, nor even much advanced, by tide ob- 

 servations made by navigators and surveyors voyaging with other 

 main objects. The later observations of the Pacific, though made 

 with great industry, have added little to the knowledge derived from 

 Cook, Flinders and King, because they were not geographically con- 

 nected with each other : and the great discrepancies of the obser- 

 vations at the same place show how little correctness the mean of 

 them, or the result, however obtained, can jjretend to. 



The results of the recent observations, with which the author has 

 been furnished by various navigators and by the Hydrographer's 

 Office, have been obtained by throwing the observations into curves, 

 according to methods formerly used and described by the author. 

 This labour has been carefully performed by Mr. D. Ross of the 

 Hydrographer's Office. 



CAMBRIDGli; PHILOSOPHICAL SOCIETY. 

 [Continued from vol. xx.xi. p. 380.] 

 May 3, 1847. — On the Internal Pressure to which Rock Masses 

 may be subjected, and its possible influence in the Production of the 

 Laminated Structure. By W. Hopkins, M.A., F.R.S. 



If a plane of indefinitely small extent pass through any proposed 



* These results follow from a series of tide observations made at Ade- 

 laide by Mr. Bealten, and at Port Essington by Sir Gordon Bremer. 



