PHILOSOPHICAL TRANSACTIONS. 



I3g 



VOL. LXVII.] 



out the evaporation of each month in inches and decimal parts of an inch. The 

 4th, the deptli of rain during each month. And the 5th, the state of the sea- 

 sons, E being prefixed to the evaporation of the whole 3 months, r to the rain, 

 and T to the mean temperature. In making these experiments, 251 grains were 

 allowed for every cubic inch of water; and 3 lb. 12 oz. of water give a depth of 

 1 inch on a circular area of 1 2 inches diameter. 



Table i, for 1772. Table ii, for 1773. Table hi, for 1774. Table iv, for 1775. 



Mths. T. Wd. Evap. Rain. Seasons. liT. Wd. Evap. Rain. Seasons.! T. Wd.Evap. Rain. Seasons. T. ,Wd. Evap. Rain. , Seasons. 



1.85 

 1.13 

 2.76 

 2.89 

 3.79 

 2.66 

 4 92 

 5.75 

 3 35 

 2.79 

 I 15 

 1.55 



3.15 

 2 37 

 0.65 

 2.47 

 4.56 

 1.42 

 1.32 

 2.21 

 6.55 

 4.57 

 6.69 

 4.3' 





5.741 

 6.17 



45. 

 9.34 

 8.35 



58. 



14.02 



10.08 



65. 

 5.49 



15.58 



,48. 



34.59 40.18! 



37 



451 



49| 



54J 



59i 



63 



66i 



67 



61i 



57 



46^ 



4U 



54 



32ll~J B. 7.10 

 4 621 V-R.10.28 

 2 45 Jt. 47J 



36.64 31.93 



39.96 40.22 



Observations. — 1. It is evident from these tables, whether we attend to sepa- 

 rate months, seasons, or years, that the depth of rain is a very erroneous index 

 of the moisture or dryness of the atmosphere. On comparing the 2 months 

 July and August of the year 1772, it appears that the temperature of the air, 

 the state of the winds, and the evaporation, were nearly the same during these 

 2 months, and yet the rain of August was more than double that of July. The 

 reason why the greater quantity of rain had no more effect than the smaller in 

 adding moisture to the atmosphere, is obvious; for on consulting the register, it 

 appears, that the rain of August fell in heavy showers, and ran oft" tiie ground 

 before it could be evaporated; while that of July, falling in small drizzling 

 showers, gave more time for its evaporation. 



Again, the temperature of the air, the state of the winds, and the evapora- 

 tion, were nearly the same during the first 3 months of the year 1773, with 

 what they were during the last 3 months of that year : the state of the air 

 therefore, with respect to moisture and dryness, must have been the same 

 during these 2 seasons ; and yet the depth of rain, in one of these seasons, was 

 much more than double what it was in the other. If we attend to whole years, 

 the same observation is confirmed. The rain of 1775 exceeded the rain of 

 1774 more than 8 inches; and hence it might be concluded, that the atmos- 

 phere was more moist in 1775 than in 1774; the reverse of this however is 

 found to be the fact : for there evaporated from a constant and determinate 

 surface of water in 1775, full 3 inches more than evaporated from the same 



T 2 



