386 



HYDROGRAPHY. 



The observations which have been made are too few to establish it, 

 or that the air has any particular direction in the upper region. My 

 stay of three weeks on the top of Mauna Loa, 14,000 feet above the 

 level of the sea, did not show it. It is true the most stormy and vio- 

 lent winds came from the southwest, but a great part of the time the 

 winds were light and variable, and from every point but southwest. 

 The temperature of this wind was low, and doubtless induced to some 

 warmer area. 



Much stress has also been laid on the fact of the descent of ashes 

 from the volcano of St. Vincent, in Barbadoes, in the year 1812, as 

 proving that the upper current was from west to east in the upper 

 regions. I think it by no means conclusive. The vast amount of 

 heat evolved may have caused a change in the aerial currents of the 

 upper atmosphere, or the ashes been attracted to Barbadoes by an 

 electrical current ; and full as plausible a solution may be advanced, 

 that the ashes remained in the upper atmosphere till the earth had 

 performed her revolution, during which period they may have imbibed 

 sufficient moisture and loss of heat to become heavier, and descend 

 over the region to the east, on the parallel with the two islands. 



In recurring to the eruption of Cosiquina, in Nicaragua, in 1835, 

 we find that the ashes were carried in all directions and to great 

 distances. 



It may indeed be doubted whether any continuous upper current 

 does move from the Equator to the Poles. I have found no proof of 

 it whatever. The upper clouds, which must move with the upper 

 currents, have always the appearance of moving from east to west, 

 within the Tropics. The opportunities for making these observations 

 rarely occur. I speak, at least, from the experience I have had. I 

 am not prepared to say that their absolute motion is such, but it is 

 the most reasonable supposition ; and if we admit that the air, in 

 rising to the higher atmosphere, loses a part of the earth's velocity, it 

 must fall behind, and have the appearance of moving in a contrary 

 direction to the earth in her rotation. 



Should this be the case, and all analogy would lead us to believe 

 that it is so, yet, when we refer to the aerial voyages which have 

 been made, we do not find anything that establishes the fact of the 

 existence of an upper current in any particular direction. 



In the celebrated voyage of Gay-Lussac and Biot, they rose to the 

 height of 13,000 feet, and were up, in their ascension, three and a 



