92 rUYSICAL GEOGRAPHY OF THE SEA, AND ITS METEOEOLOGY. 



sf^y, — Upon the proper adjustments of the dynamical forces which 

 keep up these ceaseless movements the life of organic nature 

 depends. If the air that is breathed were not taken away and 

 renewed, warm-blooded life would cease ; if carbon, and oxygen, 

 and hydrogen, and water were not in due quantities dispensed by 

 the restless air to the flora of the earth, all vegetation would 

 perish for lack of food. That our planet may be liable to no such 

 calamity, power has been given to the wayward wind, as it 

 " bloweth where it listeth," to bring down from the pure blue 

 sky fresh supplies of life-giving air wherever it is wanted, and to 

 catch up from the earth wherever it may be found, that which 

 has become stale — to force it up, there to be deflagrated among 

 the clouds, purified and renovated by processes known only to 

 Him whose ministers they are. The slightest change in the 

 purity of the atmosphere, though it may be too slight for recog- 

 nition by chemical analysis in the laboratory, is sure to be 

 detected by its effects upon the nicer chemistry of the human 

 system, for it is known to be productive of disease and death. 

 Ko chemical tests are sensitive enough to tell us what those 

 changes are, but experience has taught us the necessity of venti- 

 lation in our buildings, of circulation through our groves. The 

 cry in cities for fresh air from the mountains or the sea, reminds 

 us continually of the life-giving virtues of circulation. Experi- 

 ence teaches that all air when pent up and deprived of circula- 

 tion becomes impure g-nd poisonous. 



239. Beautiful and benign arrangements. — How minute, then, 

 pervading, and general, benignant, sure, and perfect must be that 

 system of circulation which invests the atmosphere and makes 

 *' the whole world kin?" In the system of vertical circulation 

 which I have been endeavouring to describe, we see, as in a 

 figure, the lither sky filled with crystal vessels full of life-giving 

 air continually ascending and descending between the bottom 

 and the top of the atmospherical ocean ; these buckets are let 

 down by invisible hands from above, and, as they are taken up 

 again, they carr}- off from the surface, to be purified in the labo- 

 ratory of the skies, phials of mephitic vapours and noxious gases, 

 with the dank and deadly air of marshes, ponds, and rivers. 



240. Tlieir influences ujjon the mind. — AVhenever, by study and 

 research, we succeed in gaining an insight, though never so dim, 

 into any one of the ofiices for which any particular part of the 

 physical machinery of our planet was designed by the Great 



