Daniell on Meteorological Observations. 10.5 



vapour appear to be more equable, and to be regulated by 

 more certain laws. In the winter the amount is least, and in 

 the summer greatest, reaching very nearly to double. The 

 spring and -autumn quarters are intermediate, the latter having 

 a slight excess over the former. There is, therefore, an evi- 

 dent connexion between these fluctuations and those of the 

 mean temperature, which exactly follow the same gradation. 

 Even the accidental small variations of the mean temperature, 

 from the average, are uniformly accompanied by a corresponding 

 alteration in the vapour. The utmost range appears to be from 

 0.090 to 0.631 inches, the mean pressure 0.327 inches, or rather, 

 taking into the account the correction for the night, 0.313. 



As we have been unable to trace any general eflfect produced 

 upon the motions of the barometer by the variations of the 

 vapour, so are we unable to discover any influence of the former 

 upon the latter. 



But although the force of the vapour increases with the mean 

 temperature, and reaches its maximum at the same period of the 

 year, they do not travel together with equal steps. Mr. Howard 

 deduces the difference of the heat of the seasons exactly equal ; 

 viz., 11^ degrees for each quarter. There can be no doubt that 

 this is correct. My own tables agree as nearly with the determi- 

 nation as can be expected, from so short a series. The difference 

 comes out from them, spring above winter, 13°; summer above 

 spring, 11°; autumn below summer, 12° ; winter below autumn, 

 12°. But the gradation of the constitutent temperature of the 

 vapour is as follows: — Spring above winter, 9°; summer above 

 spring, 11°; autumn below summer, 8| ; winter below autumn, 

 1 1°. The circumstances of the case prove, I think, that this 

 series approximates very nearly to the correct progression. If 

 the difference had been equal, as in the mean temperature, the 

 dryness also of the seasons would have been equal : but now, 

 from winter to spring, the capacity of the air for moisture in- 

 creasing faster than the supply, the degree of dryness must 

 also increase ; we accordingly find it in the table rising from 

 1 1° to 7°. From spring to summer the increase is nearly equal, 

 consequently the degree of dryness remains the same, 7°. 

 From summer to autumn the temperature of the air decreases 



