THE SMITHSONIAN INSTITUTION. 213 



The greatest monthly difference was in July, 1855, when it was 2.02 

 inches ; the g^reatest in any one storm was in November, 1854, a dif- 

 ference of 1 18 inclics; the storm was of about twenty-two hours' con- 

 tinuance, and the wind west. The least monthly difference was in 

 April, 1855 — 0.44 inch ; and tlic least in anyone storm was in July, 

 1855 — 0.02 inch. The storm was about twelve hours' duration, and the 

 wind northeast, and light; the air on the previous day was damp, and 

 but little wind. The quantity for the six cooler months Avas 2fj.22 

 inches in the upper, and 22.94 in the lower gage, showing a difference 

 of 6.72 inches. The quantity for the six warmer months was 16.69 

 inches in the upper, and 23.35 inches in the lower, a difference of 

 6.66 inches, showing a difference of only 0.06 inch between the warm 

 and cool months. There were seventeen storms in which the atmo- 

 sphere preceding their commencement was moist, when the difference 

 was 3.76 inches; and thirty-eight storms in which it was dry, with 

 a difference of 8.24 inches. The difference in thirteen thunder-showers 

 was 2.98 inches, in a quantity of 5.35 inches in the upper, and 8.33 

 inches in the lower; and in a quantity of 4.05 inches in the upper, 

 and 4.75 inches in the lower, there was a difference of 0.70 inch, 

 when there was little or no wind. The general result for the twelve 

 months is 32.90 inches inthe upper, and 46. 29 inches in the lower gage, a 

 difference of 13.39 inches. Of the storms, thirty of them occurred with 

 the wind easterly, and the difference in quantity was 6.98 inches; 

 eleven of them, with westerly winds, with a difference of 1.40 inches ; 

 nine, with the wind varying from west to east, and vice versa, with a 

 difference of 2.60 inches ; two, with south wind, and a difference of 

 0.21 inch ; four, with a gale from northeast, with a difference of 2.01. 

 and one varying from southwest to northeast, and a difference of 0.86 

 inch. The greatest difference for the time of continuance was in one 

 of about forty-five minutes' duration, with but little wind, when it 

 was 0.37 inch in 1.28 in quantity ; the wind was west. 



These facts are thrown out for the consideration of observers, in the 

 hope that some system may be adopted by which more accurate obser- 

 vations will be secured. 



REMARKS BY THE SECRETARY OF THE SMITHSONIAN INSTITUTION. 



The subject of the difference of rain at different elevations has re- 

 ceived much attention in this country and in Europe ; though more 

 investigations are required to settle definitely all the principles on 

 Avhich it depends. It would appear that the greater part of the 

 observed difference is due to eddies of wind, which carry the air con- 

 taining the falling drops more rapidly over the mouth of the upper 

 gage than it would pass over an equal portion of the unobstructed 

 surface of the ground. Professor Bache found, from a series of ob- 

 servations on the top and at the bottom of a shot-tower in Philadel- 

 phia, that not only was there a difference due to elevation, but also 

 to the position of the upper gage, whether it was placed on the wind- 

 ward or leeward side of the tower. It would also appear, that 

 when the air is saturated with moisture down to the surface of the 

 €arth, the descending drop would collect at least a portion of the 



