placed at different heights. 323 



on the strength of the wind, oi' the angle it makes with the ho- 

 rizon, has induced many meteorologists to infer that the in- 

 crease in the lower gauge depends almost wholly thereon : but 

 there are other causes to be taken into consideration to account 

 satisfactorily for the difference in the lower gauge ; they are as 

 follow: — 



1st. The prevailing eddy winds beneath surrounding ob- 

 structions, as hills, houses, &c. in boisterous weather, which 

 we generally experience here, when the wind comes across the 

 Atlantic Ocean. 



2d. The difference in the density of the passing yiimbi^ or 

 rain clouds, at different heights from the area of the lower 

 gauge. 



3d. The greater quantity of atmospheric air condensed and 

 precipitated with the streams of rain, when in a state of con- 

 densation, the nearer it is to the ground. 



And lastly: The deflecting currents, which turn the drops of 

 rain out of their vertical or slightly curved course into an ob- 

 hque direction, and thereby spread the bulk of rain upon a 

 greater surface. Besides these, there maybe a variety of other 

 circumstances contributing to the augmentation of rain in the 

 lower gauge ; but these, in my opinion, are the most essential ; 

 and if there is any reasonable argument in these premises, my 

 object is attained : at the same time they point out the impos- 

 sibility of an accurate demonstration of the causes, by such 

 simple diagrams as are well known to meteorologists to have 

 been injudiciously employed as the foundation of the argunients 

 upon both sides of the question ; for the solution of any ques- 

 tion on geometrical principles must appear very erroneous, 

 without the application of all the necessary corrections that 

 really belong to it. 



Those who superintend one or more rain-gauges know well 

 that the direction of the rain is influenced by the strength and 

 velocity of the wind that accompanies it ; and that it is drifted 

 nearly in its direct course, whatever the sine of its inclination 

 may be, or the angle it makes with the surface of the gauge. 

 If the lower gauge be not so much exposed to the deflections 

 of the wind and rain as the upper one, as 1 suppose it is not, 

 on account of the intervening eddy winds, &c. ; then do these 

 deflecting currents, which turn the rain from a perpendicular 

 descent, cause the greater quantity to be received in the Iowa- 

 gauge? Perhaps it may justly be said that the additional (juan- 

 tity in the lower gauge will depend on tl.e relative proportion 

 of the surfaces whereon the bulk of rain falls at the upper and 

 lower gauge. But the spread of rain wheu the building is not 

 high will, I think, be generallv as great at the upper gauge as 

 S s 2 «t 



