1847.] Examination of some Atmospheric Dust . 197 



For it is now a well recognised fact that the higher currents of the 

 atmosphere are north, say at the polar circles, and become north- 

 westerly and gradually westerly as they approach the equator, although 

 the trades are easterly and the monsoons alternating in their direction, 

 and we know also that volcanic ashes and other light matters are often 

 carried from the west to the eastward by this great upper stream of 

 westerly wind. The fall of the ashes of the volcano of Cosseguina at 

 Jamaica in 1835, 800 miles to the North-East of it and consequently 

 directly against the trade-wind, is a decisive instance of this* and I do 

 not mention others for brevity's sake. 



We are assured moreover that our dust must have come from the 

 land by its semi-animal constituents, and that it must have come there- 

 fore originally from some quarter to the westward of the meridian of 

 Ningpo, for to the eastward is the ocean, and as it was brought down by 

 a north-easterly current below, that it must have come from the north- 

 ward. In the north-west then seems the most probable direction to 

 suppose it was originally carried into the atmosphere, as I shall pre- 

 sently show, that it is improbable it could have come from Corea or 

 Japan. We may also note here, that Dr. Macgowan himself certifies 

 that no dust fell at Chusan, where he was ; Chusan lying north-east of 

 Ningpo. Hence it was either too high to fall there or it came at least 

 from the north-west. The report of the ship I do not notice here, 

 her position being uncertain, and no time given, and Loo Choo bears 

 about South-East from Shanghae, which would make the dust come 

 from the N. W. 



The volcanic ashes and dust are, it is always supposed, and this is 

 most probable, projected far enough into the atmosphere, or carried up 

 by the whirlwinds which volcanic eruptions undoubtedly create, high 

 enough to enter the upper currents of the winds, but volcanic action 

 is out of the question here, and we must look for other causes. 



Frogs, fish, seeds, pollen, &c. are well known to have been carried 

 up by whirlwinds and horizontally to great distances by currents of 

 air before their fall, and on a larger scale we have the fine dust of the 

 Sahara, which is often carried up and falls far out at sea about the 



* Ashes from the same volcano fell also on board H. M. S. Conway, in the 

 Pacific, 12U0 miles to the westward of it. Jorullo, Tuxtla and St. Vincent, are cases 

 too well known to be detailed, of ashes carried to the N. E. 



