Daniell on a new Hi/grometer. 317 



column, and its force very imperfectly by the twentieth. Upon an 

 average of experiments, I find that the winds from the NW. N. 

 NE. and E., contain 11 grain less of vapour in a cubic foot than 

 those which blow from the SE., S., SW., and W. 



In the twenty-first column I have endeavoured to describe the 

 prevailing modifications of clouds, in the nomenclature of Mr. 

 Howardi Some idea of the height of the lowest beds of these 

 aqueous condensations may perhaps be formed from the indica- 

 tions of the hygrometer. An elevation of about 530 feet causes 

 a fall in the thermometer of 1° of Fahrenheit's scale ; therefore, 

 knowing the point of condensation, and the temperature of the 

 air, if we multiply the difference by 530, we shall obtain an ap- 

 proximation to the height of the first clouds which can form, by 

 the ascent of the vapour. 



The twenty-second column closes the table with some general 

 observations. 



Plate 4, represents the comparative rise and fall of the 

 barometer and hygrometer, and of the temperature of the air 

 and vapour, taken at morning and evening, during the period 

 of the journal. The two former are laid down upon the same 

 scale, and the upper lines represent the real proportionate 

 difference of the simple and compound pressure. It will be 

 observed how much greater the variatioii of the vapour is for 

 one degree at the higher part of the thermometric scale, than 

 it is for one degree at the lower. The lower lines depict the 

 variations of temperature ; the continuous one, that of the at- 

 mosphere ; the dotted that of the point of condensation. In 

 fine weather, it will be observed that these two are widely sepa- 

 rated, while, during the time of aqueous precipitation, they 

 coincide. The converging lines shew the direction of the wind. 



It has ever been a favourite speculation with philosophers to 

 trace, in the constitution of the atmosphere, the origin of some 

 of the diseases which affect the human race. The discovery of 

 pneumatic chemistry, and the new means of questioning nature, 

 which it put into their hands, seemed, at first, to promise a solu- 

 tion of this interesting problem, and hopes were entertained that 

 the cause of epidemic and local complaints might be found in 

 Vol. VIII. Y 



