LABORS OF THE JOINT COMMITTEE. 165 



latitudes, both on account of greater heat and greater mois- 

 ture; it will ascend, and in ascending, it will recede to the 

 west, in consequence of the earth's rotation. This upper 

 current may probably be detected by the direction in which 

 the lofty columnar clouds lean ; for their tops, when they 

 rise to a great height, will be bent over in the direction of 

 the upper current. Besides, as the feathery or hazy cloud 

 spoken of above is probably formed out of the tops of col- 

 umnar clouds which have rained, this upper current will 

 most likely be indicated by the hazy clouds. Let these 

 clouds be carefully noticed and described. Is their velocity 

 uniform or various ? Does their acceleration indicate rain ? 



Does their increase in number indicate rain? 



The observer will be careful to distinguish between violent 

 storms and ordinary rains ; for it may be that ordinary rains 

 are very irregular in the direction of their motion, the tops 

 of clouds producing them not reaching into the uppermost 

 current, which is probably nearly uniform in its direction, 

 while the tops of clouds producing tornadoes, may all reach 

 into the uppermost current, and thus great uniformity in 

 the direction of their motion may be produced. Mr. Red- 

 field has shown that there is a remarkable uniformity in the 

 progressive motion of storms or hurricanes, which traverse 

 the West India islands, all moving in the direction which 

 theory would seem to give to the uppermost current as it 

 passes off from the equator towards the poles. The greater 

 heat and higher dew point of the inter-tropical air will 

 cause it to be about one sixth lighter than air in the frigid 

 zones, and of course it will stand proportionally higher and 

 will therefore roll off towards the poles, carrying with it in 

 some measure, the diurnal velocity, which it had at the 

 equator ; and so moving faster than the earth at the latitude 

 which it has reached. In confirmation of this theoretical 

 result it is known that the highest of all our clouds in the 

 latitude of Philadelphia, come constantly from near the 



