Daniell on a new Hi/grometer. 133 



amounted nearly to three times the quantity of the whole of 

 the three remaining periods. 



Again; from the mean of 178 experiments we learn, that the 

 degree of dryness in the afternoon exceeds that of 10 o'clock in 

 the morning by 1°, while the degree of dryness of the night 

 falls short of the same by li°. 



The evaporation of morning, afternoon, and night are re- 

 spectively as 16, 22, and 6, and the weight of vapour, in the 

 space of a cubic foot, is less at night by 0.024 than in the after- 

 noon. This latter effect arises, no doubt, from its precipitation 

 upon the earth's surface, when cooled by radiation, and is the 

 amount probably of the aqueous precipitations of dew and 

 hoar-frost. The amount of the depression of temperature from 

 radiation, from an average of 100 experiments, is 4° per night. 



The greatest quantity of vapour observed during the half 

 year was 6.863 grains in the cubic foot with the wind from 

 the south-west, the least quantity 1.065 grains with the wind 

 from the east. 



I shall conclude with one observation upon the correction 

 to be applied to barometrical measurements from the use of the 

 hygrometer. In my last paper I suggested the application of 

 this correction, and mentioned, as a case most particularly 

 liable to be affected by it, the estimation of the heights of the 

 Himalaya Mountains. I was at that time unacquainted with 

 the temperature of the atmosphere at the two places of obser- 

 vation, and was reduced to supposition to elucidate the ex- 

 ample. Since then these data have been furnished by the 

 Quarterly Review *, and we may now make the calculation 

 upon much surer grounds, and reduce the probability of error 

 to much narrower limits. The observations made by Captain 

 Webb on the crest or highest ridge of Nitee Ghaut, taken on 

 the 21st of August, at three P.M., by the mean of four baro- 

 meters, the thermometer standing at 47, gave a mean of 16.27 

 inches. 



From a journal of the weather, kept by Colonel Hardwicke, 



• Quarterly Review, No. xliv. p. 423. 



