-1859] WRITINGS OF JOSEPH HENRY. 281 



have been tabulated for the Smithsonian Institution, under 

 the direction of Professor Bache, by Mr. Schott, of Washing- 

 ton, give the same direction to the northern current at the 

 surface of the earth within the polar circle. 



That the prevailing motion of the system B is in the direc- 

 tion exhibited by the arrows, is abundantly shown by the 

 fact of the prevalency of the southwest wind, particularly in 

 the summer, over the whole of the temperate zone; and that 

 this upper current of the same system is southward and 

 eastward, or in other words from the northwest, is attested 

 by aeronautic observations in this country, and in Europe. 

 The celebrated American aeronaut, Mr. John Wise, (from 

 the experience of upward of two hundred balloon ascen- 

 sions,) has stated to the writer, that while the current at 

 the surface of the earth is from the southwest, at a variable 

 elevation of two miles or less, the wind becomes nearly 

 due west, and at a still greater elevation it blows from the 

 northwest. The direction of the intermediate stratum is 

 probably due to the resultant action of the two, and this 

 would naturally result from the almost constant action of 

 ascending currents, passing with every fall of rain from the 

 lower to the upper. A similar testimony is given for West- 

 ern Europe by the aeronautic experience of Messrs. Green 

 and Mason. According to this, though the prevailing wind 

 at the surface is from the southwest, at an elevation of 10,000 

 feet the current is invariably from some point north of west. 

 Moreover, observations on the direction of the ashes of vol- 

 canoes prove the same direction of the upper current. In 

 the summer of 1783 the smoke of an eruption of a volcano 

 in Iceland was diffused over England, Germany, and Italy. 

 From another eruption of a volcano in the same island, in 

 1841, the ashes were carried by a northwest upper current 

 and deposited on the decks of vessels in the Irish Channel. 



Though the prevailing direction of the currents of the 

 system is given in B, (in Fig. 5,) yet the stability of this 

 system is by no means equal to that of A, or even that 

 of C, since in some cases its direction is apparently entirely 

 reversed. The northwest upper current, mingling perhaps 



