214 PHYSICAL GEOGRAPHY OF THE SEA : 



lieving the upper regions of the atmosphere to be traversed 

 by currents of lesser density, but as determinate in space, 

 time, and direction, as the winds which sweep periodically 

 over the surface below. The general equilibrium is ever 

 maintained; and this can only be effected by circuits and 

 counter currents at different heights, according to the differ- 

 ences of temperature of each. The inference here approaches 

 to a demonstration of the fact, though not reaching it by 

 actual observation. 



We cannot speak with the same assurance of a speculation, 

 which however is sanctioned by eminent names, viz. that 

 the more sudden and violent gales of wind, the tornadoes 

 and whirlwinds of the seas, are due to the upper currents of 

 air bursting abruptly into those of lower level ; and by their 

 different direction of movement, different temperature, and 

 possibly difference of electrical state, begetting the various 

 phenomena of storm on the ocean beneath. No better theory 

 has yet been proposed for these sudden hurricanes ; and in 

 default of such, we must admit it as one of the many 

 meteorological questions open to future research. 



We should abuse the patience of our readers, were we to 

 dwell longer on the subject of atmospheric currents thus 

 encircling the globe, and, under their various conditions, 

 aiding or endangering the labours of man on the seas. The 

 only remark we have to add respecting Captain Maury's 

 chapters on the atmosphere is, that he does not sufficiently 

 allude to the influence of the variable weight of this great 

 aerial ocean upon the ocean of waters below. Those who 

 have attended to the phenomena and theory of the Seiches 

 in the small basin of the Lake of Geneva, or witnessed the 

 frequent and abrupt oscillations of a forty-feet water baro- 

 meter, will be able to appreciate this element of unequal 

 atmospheric pressure, as applied to the great watery surface 

 of the globe. Nor do we find any allusion by our author to 



