io Preface. 



observations, and more especially of the sounding operations 

 carried on on board H.M.S. " Challenger" during her cruise 

 round the world, in so far as they throw any light upon the 

 distribution of depth, temperature, and currents in the different 

 oceanic basins which have been explored. 



The advance made in our days towards a satisfactory solu- 

 tion of the problem of oceanic circulation will probably be 

 recorded with due completeness by abler hands ; meantime, I 

 am not without hope that the contents of this essay may find a 

 welcome amongst those who have followed with interest the 

 progress of the numerous expeditions sent out of late years to 

 clear up the mysteries of the ocean. 



JOHN JAMES WILD. 

 London, May, 1877. 



