78 PHILOSOPHY OF STORMS. 



The prime object of this circular is to obtain a complete 

 knowledge of all the phenomena accompanying one or more 

 storms of rain or hail, not only where the violence of the 

 storm is felt, but at and beyond its borders, its beginning 

 and its end. 



For this purpose you are requested, immediately on re- 

 ceiving this circular, to commence a journal of the weather, 

 noting the direction of the wind at the surface of the earth 

 and in elevated strata, as indicated by the clouds, which 

 may frequently be seen at different elevations, moving in 

 different directions ; the upper current of all being at Phi- 

 ladelphia, generally from some western point. Let the 

 strength and direction of the wind, and the appearance of 

 the heavens as to clear or cloudy, and the character of the 

 clouds, according to your own mode of description, be noted 

 at least three times a day, as near the following hours as 

 convenient : 7 A. M., 2 P. M., and sunset. Let the heav- 

 ens, however, be examined very often, so that any sudden 

 change may not pass unobserved, especially in the direc- 

 tion of the wind ; and when any occurs, let it be noted, 

 with its time, under the general head of " Observations." 



The plan which we recommend in observing slow-mov- 

 ing clouds, is to keep the head steady in one place, with 

 the top of a chimney, or some distant fixed object, between 

 the eye and any remarkable point of the cloud, until this 

 point shall have moved so far from behind the object as to 

 leave no doubt of its direction. 



As to upper and lower strata, when one passes under the 

 other, there is an optical deception to be guarded against 

 when the upper one moves with the greatest angular velo- 

 city. The deception may generally be avoided by noticing 

 which cloud is obscured by the other as they pass. Some- 

 times, also, an upper current of air may be detected when 

 there is but one stratum of clouds, if these are of the col- 

 umnar snowy -topped kind, which are frequently seen in a 



