528 



Captain Spratt on the Undercurrent 



[June 15, 



I have chosen a particular case, but it is manifest that the equation 



could be treated in the same manner. There will be eight possible forms 

 of solution of the class we have here considered, but in practice the number 

 of trials will be much reduced if we do not consider the incommensurable 

 roots of (n). 



XI. " On the Undercurrent Theory of the Ocean,, as propounded by 

 recent explorers." By Captain Spratt, C.B., R.N., F.R.S. 

 Received June 15, 1871. 



The universal undercurrent theory so fascinatingly advocated by Maury 

 and others, and more recently by the late Dr. Forchhammer, has now been 

 so remarkably supported and maintained in the enlarged views pronounced 

 by Dr. Carpenter in his recent papers and lectures before the Royal and 

 other societies, and is of so interesting and important a nature in connexion 

 with the study of the laws regulating the natural history and geological 

 results of the past, as well as of the phenomena in progress in the ocean 

 and seas in communication with it, that the assumed facts and data upon 

 which they are based deserve, and indeed require, in the interest of sound 

 science and philosophy, to be carefully considered and analyzed before they 

 can be accepted as a grand law such as is implied in the views or theory. 



Dr. Carpenter has put forward certain axioms as " propositions " or 

 fundamental principles, as necessary results from the influence of rivers 

 and rain, temperature, evaporation, and density upon the surface and deeps 

 of all seas that are in communication. I feel it necessary to give the more 

 important of these, as being the basis of his theory*. 



" No. III. That wherever there is a want of equilibrium arising from 

 difference of density between two columns of water in communication with 

 each other, there will be a tendency towards the restoration of equilibrium 

 by a flow from the lowest stratum of the denser column towards that of 

 the lighter, in virtue of the excess of pressure to which the former is 

 subjected. 



"No. IV. That so long as the like difference of density is maintained, 

 so long will this flow continue ; and thus any agency which permanently 

 disturbs the equilibrium in the same sense, either by increasing the density 

 of one column, or by diminishing that of the other, will keep up a 

 permanent flow from the lower stratum of the denser towards that of the 

 less dense. This constant tendency to restoration of equilibrium will 

 keep the actual difference of density within definite limits. 



"No. V. That if there be at the same time a difference of level and an 



* See anteh, p. 211. 



