146 THE PHYSICAL GEOGRAPHY OF THE SEA. 



with tlie conditions — electrical and others — favorable to its de- 

 scent, and that these conditions, as with the vapor, may occur now 

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

 the same atmospherical vein or general direction, my investiga- 

 tions would suggest, and Ehrenberg's researches prove. Judging 

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

 in the upper regions of the atmosphere are remarkable for their 

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

 ness of limits, so to speak. We may imagine that certain elec- 

 trical 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 disturbances in the atmosphere and the occurrence 

 of these showers, though it does not enable us to determine the 

 true rate of motion in the general system of atmospherical circu- 

 lation, yet assures us that it is not less on the average than a cer- 

 tain rate. We can not pretend to prescribe the conditions requi- 

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

 from the smoke-dust — as the particles of visible smoke may be 

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

 dew, causing it to descend in the black fogs of London. Any cir- 

 cumstances, therefore, which may cause the dust that ascends as a 

 straw-colored cloud from the Orinoco to radiate its caloric and 

 collect moisture in the sky, may cause it to descend as a red fog 

 in the Atlantic or Mediterranean. 



832. I do not offer these remarks as an explanation with which 

 What ia the agent wc ought to TCSt Satisfied, providcd other proof can 

 acTOss^the calm belts? be obtained; I rather offer them in the true philo- 

 sophical spirit of the distinguished microscopist himself, simply as 

 affording, as far as they are entitled to be called an explanation, 

 that explanation which is most in conformity with the facts be- 

 fore us, and which is suggested by the results of a novel and beau- 

 tiful system of philosophical research. It is not, however, my 

 province, or that of any other philosopher, to dictate belief Any 

 one may found hypotheses if he will state his facts and the rea- 

 soning by which he derives the conclusions which constitute the 

 hypothesis. Having done this, he should patiently wait for time, 

 farther research, and the judgment of his peers, to expand, con- 

 firm, or reject the doctrine which he may have conceived it his 

 duty to proclaim. Thus, though we have tallied the air, and put 



