RED FOGS AND SEA BREEZES. 145 



Islands are situated ; tliey are in the direction wliicli theory gives 

 to the upper current of air from the Orinoco and Amazon with its 

 '' rain dust," and they are in the region of the most frequent 

 showers of " rain dust :" all of which, though they do not absolutely 

 prove, are nevertheless strikingly in conformity with this theory 

 as to the circulation of the atmosphere. 



331. It is true that, in the present state of our information, we 

 Condition rpquisite camiot tcll wliv tliis "rain dust" should not be 



to the production of in • • , i ^ n n • , ^ 



a sea'fog. gradually precipitated irom this upper cmTcnt, and 



descend into the stratum of trade-Avinds, as it passes from the 

 equator to higher northern latitudes ; neither can we tell why the 

 vapom' which the same winds carry along should not, in like 

 manner, be precipitated on the way ; nor why we should have a 

 thunder-storm, a gale of wind, or the display of any other atmo- 

 sj)herical j)henomenon to-morrow, and not to-day : all that we can 

 say is, that the conditions of to-day are not such as the pheno- 

 menon requires for its own development. Therefore, though we 

 cannot tell why the " sea-dust " should not always fall in the same 

 place, we may nevertheless suppose that it is not always in the 

 atmosphere, for the storms that take it up occm' only occasionally, 

 and that when up, and in passing the same parallels, it does not, 

 any more than the vapour from a given part of the sea, always 

 meet with the conditions — electrical and others — favom^able to its 

 descent, and that these conditions, as with the vapom-, may occiu' 

 now in this place, now in that. But that the fall does occur 

 always in the same atmospherical vein or general direction, my 

 investigations would suggest, and Ehrenberg's researches prove. 

 Judging by the fall of sea or rain dust, we may suppose that the 

 ciUTents in the upper regions of the atmosphere are remarkable ^r 

 their general regularity, as well as for their general direction and 

 sharpness of limits, so to speak. We may imagine that certain 

 electrical conditions are necessary to a shower of " sea-dust " as 

 well as to a thunder-storm ; and that the interval between the time 

 of the equinoctial distm^bances in the atmosphere and the occm-- 

 rence of these shoAvers, thoucfh it does not enable us to determine 

 the true rate of motion in the general system of atmospherical 

 circulation, yet assm^es us that it is not less on the average than a 

 certain rate. We cannot pretend to prescribe the conditions requi- 

 site for bringing the dust-cloud down to the earth. The radiation 

 fi'om the smoke-dust — as the particles of visible smoke may be 

 called — has the effect of loadinsr each little atom of smoke with 



