4o6 The Ohio Naturalist. [Vol. Ill, No. 6. 



root action is practically nothing, then evaporation into an air of 

 low relative humidity may take place to such an extent as to 

 prove injurious. No water is taken by the roots from the soil to 

 take the place of that evaporated. During the growing sea.son 

 the effect of a low relative humidit}', as in case of hot, dry winds, 

 is too well known to need further comment. 



The relative humidity of the Northern and Western United 

 States is from five to ten per cent, higher in winter than in .'■um- 

 mer, but in the Gulf States and lower Atlantic States conditions 

 are fairly constant the year through. The highest relative humid- 

 ity is to be found along the northern Pacific coast and to the 

 east and southeast of Lake Superior. The westerly air currents 

 rising from the Pacific to the crest of the mountains are consid- 

 erably cooled and saturation is produced to such an extent that 

 much of the moisture is precipitated and never gets over the 

 mountains. In this manner a high relative humidity is brought 

 about along the coast. 



In the case of the Great Lakes we have another factor in opera- 

 tion. The westerly air currents in drifting across the waters 

 are often considerably cooled and also take up more or less 

 moisture, so that a region of high relative humidil>- nuist re.^ult 

 east of the lakes. 



Ohio presents some rather peculiar conditions with respect to 

 humidity. As may be seen in the plate, the January map shows 

 a streak coming down from the northwest and tra\-ersing the 

 State diagonally in which the relative humidity is above eighty 

 per cent. The air in that streak is just as "moist" as the air of 

 Florida. From Map II of the January article referred to it may 

 be seen that this streak includes that part of the State having the 

 least total annual precipitation, and only a small part of those 

 sections of the State having the greatest annual precipitation. 

 The total annual precipitation and the relative humidity appear 

 to have no connection whatever. 



Turning again to the January article, Map VII shows that 

 during winter the least average minimum temperatures occur in 

 the northwestern and central portions of the State, and are central 

 in the region of high relative humidity. The inference to be 

 drawn is that the higher relative humidity results from the lower 

 temperature. It is not readily apparent, however, why this region 

 should have its longer direction at right angles to the prevailingly 

 southwestern direction of the winds, but perhaps this may be due 

 in some measure to the difference in temperature of winds from 

 different directions. The general direction of storms in our region 

 is from we.st to east. Around the areas of low barometric pressure, 

 usually the warm stormy areas, the winds revolve in a counter- 

 clockwise direction, while around areas of high barometric pres- 

 sure, those of clear cold weather, the revolution of the wind is u\ 



