243 OF TEMPERATURE CHAP. 9. 



densation of the vapour in the case of Rain. 

 But on what principle can we account for the 

 increase both of Temperature and Pressure, 

 during such condensation ? On the 20th and 

 21st July, 1811, Rain kept falling in large drops 

 almost all day, with a rising Barometer, and no 

 depression of Temperature, (making allowances 

 for the interception of the Sun's rays,) while 

 evaporation continued to be considerable. 



It has been remarked by M. Howard, that if 

 the state of the Barometer, during any period 

 of the Moon, be examined, it will be found to 

 have been highest or lowest about the time of 

 the Full and New Moon, as may happen ; but 

 that the mean state of that instrument usually 

 happens about the lunar quadratures. As far 

 as my own observations enable me to decide 

 this connexion is observable in the majority of 

 instances. 



I once thought that the mean state of the 

 Barometer of a given number of day's observa- 

 tion varied, in some measure, according to the 

 Moon's perigee and apogee ; that is, that it was 

 higher with the latter than with the former: 

 but subsequent researches convinced me, that 

 the exceptions were almost as numerous as the 

 cases corresponding to the rule. 



