540 THE AIR AND LIFE. 



waters could stand. This however adds no new iihase to the question. 

 There are for all, without excejition, certain increases or decreases of 

 pressure that prove fatal, and from a general standpoint there is no 

 importance in the fact that their adaptations are different, for theditfer- 

 ences are in degree, not in kind, and the nature of the ])henomeua 

 remains unchanged. 



We are then justified in saying that while the influence exerted by 

 variations of pressure over animate life is apparently mechanical it is 

 actually a chemical one. Does this also apply to the action of atmos- 

 pheric movements'? If we leave out of consideration the ett'ect on the 

 chemical composition of air had by the winds and other atmospheric 

 motions in promoting a ditfusion of such gases as are produced in abund- 

 ance at various places, together with the regulating action of the ocean, 

 we shall satisfy ourselves that the influence of these movements is purely 

 physical. Looking at this question from the particular point of view 

 of this discussion, these movements must be considered as regulators of 

 temperature and as propagators of certain forms of life. They nuist of 

 necessity be the former, since winds are chiefly caused by unequal heat- 

 ing of the ground and air in diflerent places, and, if there were no wind, 

 the temperature would soon become unbearable and noxious to life. 

 Without winds, the water from the ocean would not be carried overland 

 by the clouds, and great droughts would follow. Without winds, air 

 vitiated by local causes would remain in that condition; impure gases 

 from natural or artificial sources would disperse but slowly. Wind is 

 the cleaner, the sweeper of the air; it drives it, stirs it, mixes it, trans- 

 ports' it over every land and every sea, and insures a general distribution 

 in the whole atmosphere of such elements as are produced in super- 

 abundance at any one point. It maintains the purity of the atmosphere, 

 or at least its homogeneous composition, and aids in preventing exces- 

 sive inequality of temperature. 



Atmospheric movements also assist in regulating the individual tem- 

 perature of men and homeothermic animals. Wind keeps air from 

 becoming saturated with moisture. We all know how oppressive heat 

 is in a warm and moist atmosphere when perspiration is not easily evap- 

 orated, and on the other hand, absolutely dry air is not without its incon- 

 veniences and irritates the lungs. By distributing in every part of the 

 atmosphere the moisture which is pleutifully produced in some of its 

 parts, wind does living beings a great service. It is also useful in pro- 

 moting the dispersion of a number of insects and vegetables, which it 

 carries afar, beyond the sea, to distant islands and continents. But it 

 also is objectionable, in that it scatters at the same time the pathogenic 

 microbes and spreads diseases of which they are the cause. I shall not 

 now dwell on this point, for it will claim our attention later. It is 

 enough now to note the simultaneous influ(?nce for good and evil whi(;h 

 is exercised by atmospheric movements, the nature of such influence 

 being entirely due to that of the objects transported by them. 



