Daniell on a}ieu' Hi/grometer. 315 



perature of the air 65°, with a moderate breeze. The number 

 opposite 52° in the fourth column is 2.06, and that opposite 

 65° is 3.16; the difference 1.1 grain, is the evaporation per 

 minute. 



I shall now proceed to explain the annexed journal of my 

 observations upon the weather, premising that the instruments 

 which I employ are all placed in an eastern aspect, out of the 

 direct rays of the sun, and as much as possible secured from the 

 influence of surrounding objects. 



The first, second, and third columns contain the date and 

 hour of the observation, and the moon's age. The fourth ex- 

 hibits the pressure of the whole atmosphere, as measured by 

 the barometer ; and the fifth, the continuous rise and fall of that 

 instrument. The sixth column shows the pressure of the aque- 

 ous atmosphere alone : by a comparison of this with the pre- 

 ceding, it will be observed how little the latter has to do with 

 the comparatively great variations of the compound atmosphere. 

 If any connexion can be traced at all, it is rather that the pres- 

 sure of the vapour increases as the whole diminishes, and 

 vice versd, than the contrary. 



The seventh column gives the temperature of the air, at the 

 time of observation ; and the eighth, that of the vapour or the 

 point of condensation. The ninth shews the difference between 

 the two. The probability of aqueous precipitations is in inverse 

 proportion to these numbers ; and if it should be thought ne- 

 cessary to speak of the indications of the hygrometer in degrees 

 of a scale, these are the numbers which will express those de- 

 grees. The extent of the scale, as far as I have observed, is 

 •20". 



The tenth column exhibits the weight of acqueous vapour 

 actually existing in a cubic foot of the atmosphere ; the eleventh, 

 the maximum quantity of the same, which might exist if the 

 temperature of the air were to fall to the temperature of the 

 vapour; and the twelfth, the maximum quantity which might 

 exist, if saturation were to take place at the temperature of 

 the air. It will be observed that these three coincide, when pre- 

 cipitation is actually taking place. From their af)proximation 



