LABORS OF THE JOIJNT COMMITTEE. 147 



The Barometer Should be hung perpendicularly, and 

 the screw at the lower end loosened, until the mercury 

 ceases to fall. When taking an observation, the barometer 

 should always be slightly agitated or patted, to obviate the 

 effects of friction. The movable index or vernier should then 

 be set to the top of the mercury, and its height be read off 

 to the nearest ^ of an inch. Daring the passage of storms, 

 it will be highly important to note, as near as may be, the 

 moment of greatest depression. 



Wind and Clouds. The wind and clouds should both be 

 noted in the direction from which they are coming: thus, 

 if both proceed from the west, they should be marked ^ ; 

 and if the wind should be east, and the clouds from the 

 south west, they should be marked ^, the lower letters 

 always denoting the wind, arid the upper letters the clouds. 

 Also the force of the wind and velocity of the clouds may 

 be denoted by the figures, 0, 1, 2, 3, 4, 5 : signifying a 

 calm, or no motion in the clouds; 1, a very gentle breeze, 

 or a very slow motion in the clouds ; and so on till 5, which 

 signifies a very strong gale. According to the same scale, 

 a tornado would be marked 10. 



For example, should the wind be a moderate breeze from 

 the north, and the clouds moderately fast from the W. S. W., 

 the whole would be marked w -^- 2 ; and should the air be 

 nearly calm below, and the clouds very fast, all in the same 

 direction as before, it would be noted w ^' ^' 5 \ ^ llt m case 

 there should be two or three currents of clouds, the 

 fact must be noticed among the general observations, or 

 thus, JLJL the uppermost letter denoting the upper clouds, 

 the middle letter the lower clouds and the lowest letter the 

 wind ; the velocity of each current being expressed by 

 numbers as above. 



The Dew Point. For the method of finding dew point, 

 see first circular (98). 



Clearness of Shy. The clearness of the sky may be 



