-1859] 



WRITINGS OF JOSEPH HENRY. 261 



Suppose the wind is coming from the west, and striking with 

 force against the side of the tower which faces that direction, 

 it will be deflected upward, and thus retard the fall of rain 

 on the near side of the roof of the tower, and precipitate it 

 over the leeward side, while the portion of wind which passes 

 around the circumference of the tower, near its top, will be 

 accelerated, and will by the latter action impart its motion 

 to the air on the north and south sides of the roof of the 

 tower, which will cause the drops of rain to be crowded to- 

 gether on the leeward side. 



The effect of the upward deflection of the wind and the 

 acceleration of the rain, under conditions such as we have 

 just described, are strikingly illustrated by the observations 

 which were made on the high tower of the Smithsonian In- 

 stitution, Three gauges were placed on the roof of this 

 tower, — one on the west, one in the centre, and a third on 

 the east side. Now if the prevailing wind be west, we should 

 expect (if the theory which we have presented is correct,) that 

 the west gauge would contain the smallest quantity of water, 

 the middle one next, and the one on the east side the great- 

 est; and this was found to be actually the case. 



The action of the wind also materially affects the amount 

 of water which falls in different gauges of different forms 

 and sizes at the surface of the earth. It is well known that 

 different gauges, which indicate the same amount of rain in 

 calm weather, diff'er materially in the quantity of water 

 which they collect in high winds. If the gauge be of con- 

 siderable size, and project above the surface of the earth, the 

 air will be deflected upward and accelerated around it, as in 

 the case of the tower ; nor is this result obviated by sinking 

 the large gauge to the level of the earth, since in that case 

 the current curves down into the gauge and tends to carry 

 out a portion of the falling drops on the opposite side. From 

 a series of experiments made at the Smithsonian Institution, 

 and continued for several years, it is found that a small 

 cylindrical gauge, of 2 inches in diameter, and about 6 inches 

 in length, connected with a tube of half the diameter, to re- 

 tain and measure the -water, gives the most accurate results. 



