8 Preface. 



chances of success, the solution of several problems, for which 

 no complete answer has as yet been found. One of these 

 problems is that of " Oceanic Currents." Ever since Lieutenant 

 Maury, in his admirable work on the Physical Geography of 

 the Sea, undertook to explain the probable causes of the 

 " beautiful system of circulation " by which " cooling streams 

 are brought from the Polar Seas to temper the heat of the 

 Torrid Zone," this question has been the subject of frequent 

 controversy ; but I believe I am correct in stating that none of 

 the theories advanced in explanation of this gigantic natural 

 phenomenon have met with general acceptance, nor has any 

 satisfactory solution of the problem been offered. 



One of the principal causes of this failure will be found in 

 the want which existed, until within late years, of the necessary 

 appliances and opportunities for ascertaining the conditions 

 which prevail in every part of the ocean, from its surface down 

 to the bottom. The scientific explorer possessed neither proper 

 sounding apparatus, nor instruments capable of resisting the 

 enormous pressures to which they are subject at great depths* 

 nor the aid of steam-power for expediting the hauling in of 

 miles of sounding-line or dredge-rope ; and last, not least, % he 

 found no Government willing to open the national purse in 

 favour of scientific experiments planned on a scale the expense 

 of which exceeded the resources of even wealthy individuals, 

 and which were absolutely beyond reach of the proverbially 

 poor devotee of Science. In the absence of these indispensable 

 helps, it was next to impossible to secure observations sufficiently 

 reliable to afford a criterion in judging between the numerous 

 theories which have been advanced, however sound the premises 

 and logical the deductions on which they were based. 



Another source of failure may be traced to the attempt to 

 explain a highly-complex phenomenon by the operation of a 

 single cause, and to the consequent neglect of one or other of 



