132 Daniell on a new HygrCtmeter. 



Evaporation 0.08 grs. 



Temperature 38 



For the third period — 



Pressure of atmosphere 29.73 ms. 



Ditto of vapour 0.219 



Weight of ditto in a cubic foot 2.505 grs. 



Degree of dryness .....>• 1 



Evaporation 1 -03 



Temperature 32° 



For the fourth period — 



Pressure of the atmosphere 29.79 ins. 



Ditto of the vapour 0.225 



Weight of vapour in a cubic foot 2.580 grs. 



Degree of dryness li° 



Evaporation per minute from a surface six inches in 



diameter 0.06 



Temperature 34 



It is curious to observe the progressive changes of the at- 

 mospheric vapour in these different divisions. These six months 

 constitute the dampest half of the year, but dampness, -we. 

 perceive, does not consist in the greater quantity of vapour in 

 the air, but in the approximation to the point of saturation of 

 the existing temperature. In the first six weeks, from the end 

 of August to the middle of October, the weight of vapour in a 

 cubic foot was, upon the average, 4.697 grs. and the mean 

 degree of dryness 6|-. From the end of November to the be- 

 ginning of January, the weight of vapour was not more than 

 2>505 grs., and the degree of dryness only 1°. Hence is apparent 

 the reason why the quantity of rain is greater in the summer 

 months than in the winter, although the number of rainy days 

 is less. The dampest period of the year is from the middle 

 of November to the beginning of January. From that time to 

 the end of February, the dryness sensibly increased, and in 

 March, it will be hereafter seen, has reached the average de- 

 gree of the autumn month. Evaporation is in compound pro- 

 portion to temperature and dryness, and, in the first six weeks, 



