THE ATLANTIC OCEAN. 213 



does not clearly separate the known from the unknown. 

 His volume is replete with ingenious suggestions, but they 

 are not methodised enough for the uses of the common 

 reader, who will probably rise from the Chapters on winds 

 and atmospheric currents, his head confused by a whirl of 

 facts and theories and questions, as fleeting as the very air of 

 which he has been reading. It must be admitted that this 

 subject of the Winds of the ocean whether permanent, 

 periodical, or variable is one of very difficult and intricate 

 kind. The differences of temperature between the tropical 

 and arctic regions, and the influence of the earth's diurnal 

 rotation upon the currents of air thus produced, afford us a 

 rational theory of the trade-winds. The periodical monsoons 

 of the Indian Ocean, though depending in part on the same 

 causes, are singularly modified by the proximity of great 

 continents, islands, and mountain ranges ; and though well 

 known to practical navigators, their character is less certain 

 and their interpretation more obscure. Still slighter is our 

 knowledge of the variable winds, in those narrower seas where 

 the influences of the land become predominant over those of 

 the water ; phenomena in which we in England have great 

 practical concern, but to which it is at present difficult to 

 give any systematic form. 



The Barometer, though less certain here than on the wide 

 Oceans of the globe, is still the instrument on which we may 

 best depend ; and the recent extension of its uses (aided by 

 the electric telegraph), around the English coasts, will every 

 year save hundreds of lives among the sailors and fishermen of 

 our shores. It must however be kept in mind that our direct 

 knowledge of the winds is derived from the lower strata of 

 the atmosphere only. The aspects of clouds often show to 

 the eye different or opposite currents at different heights : 

 observations in balloons testify the same thing. Beyond this 

 our conclusions, though inferential only, warrant us in be- 



