-1859] WRITINGS OF JOSEPH HENRY. 305 



in winter very nearly the same for several successive periods. 

 For example, most persons can remember the successive 

 occurrence of a series of storms on Sundays. In one case 

 we recollect this to have taken place six times in succession. 

 There is nothing in this particular day to induce the occur- 

 rence of a storm, but merely it will be more likely to be 

 rerhembered when it happens at this time; and although 

 the interval between two storms may not be precisely seven 

 days, yet it may differ so little from this that a part of the 

 first and sixth Sundays may be included in the cycles of 

 disturbance. 



The wind as a general rule tends to flow towards the axis 

 of the storm from each side, but at the surface of the earth, 

 diversified with hills and valleys, the direction is far from 

 being as regular as at first sight might be expected. Besides 

 this, since the commotion of the atmosphere is usually 

 divided into a number of separate groups — each having a 

 separate ascending column or belt to which the in-blowing 

 air is directed, — the arrows on the map indicating the direc- 

 tion of the winds generally present a very complex system 

 of currents. On this account also, the rain does not simul- 

 taneously fall along an extended line from east to west but 

 in separate places, the position of which is determined 

 probably by the greater amount of moisture, and conse- 

 quently the more intense action of the ascending current. 

 As the storm approaches the eastern part of the United 

 States however the in-blowing air to supply the up-moving 

 current draws in the air from the ocean, charged with 

 moisture ; which being constantly supplied, the action may 

 continue for several days, and the storm may perhaps be- 

 come stationary, giving rise to prolonged easterly currents. 



It would appear however from observations at the Smith- 

 sonian Institution, that the northeast storms are produced by 

 the rarefication of air on the east side of the Alleghany 

 Mountains, being frequently independent of a previous in- 

 terior storm from the west. 



A considerable number of storms has been mapped in 

 accordance with the plan first adopted by Professor Loomis, 



20-2 



