88 THE PHYSICAL GEOGRAPHY OF THE SEA. 



wherever it is wanted, and to catch up from the earth wherever 

 it may be found, that which has become stale ; to force it uj), 

 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 recognition by chemical analysis in the labora- 

 tory, is sure to be detected by its effects upon the nicer chemistry 

 of the human system, for it is known to be productive of dis- 

 ease and death. No chemical tests are sensitive enough to tell us 

 what those changes are, but experience has taught us the neces- 

 sity of ventilation 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. 

 Experience teaches that all air when pent up and deprived of 

 circulation becomes impure and poisonous. 



239. How minute, then, pervading, and general, benignant, 

 Beautiful and bcniga ^urc, aud pcrfcct must bc that system of circulation 

 arrangements. which luvcsts the atmosphcrc and makes the " whole 

 world kin !" In the system of vertical circulation which I have 

 been endeavoring to describe, we see, as in a figure, the lither sky 

 filled with crystal vessels continually ascending and descending be- 

 tween the bottom and the top of the atmospherical ocean full of 

 life-giving air ; these buckets are let down by invisible hands from 

 above, and, as they are taken up again, they carry off from the 

 surface, to be purified in the laboratory of the skies, phials of 

 mephitic vapors and noxious gases, with the dank and deadly 

 air of marshes, ponds, and rivers. 



240. Whenever, by study and research, we succeed in gaining 

 Their influences up- ^^ lusight, though ucvcr SO dim, iuto any one of 

 on the mind. ^-^q ofiices for which any particular part of the 

 physical machinery of our planet was designed by the great Ar- 

 chitect, the mind is enriched with the conviction that it has com- 

 prehended a thought that was entertained at the creation. For 

 this reason the beautiful compensations which philosophers have 

 discovered in terrestrial arrangements are sources of never-failing 

 wonder and delight. How often have we been called on to ad- 

 mire the beautiful provision by which fresh water is so consti- 

 tuted that it expands from a certain temperature down to freez- 

 ing ! We recognize in the formation of ice on the top instead of 



