at Leith Fort, every Hour of the Day, in 18^4 and 1825. 27 



H. ' 

 Interval between Maximum and following Minimum, 14 20 



Interval between Morning and Evening Mean, - 11 14 



Interval between Minimum and Morning Mean, - 4 13 



Interval between Evening Mean and following Minimum, 8 33 



The determination of the exact times of mean temperature 

 throughout the year, furnishes us with the two best times of the 

 day for recording the indications of the thermometer. These 

 times are obviously 9 h 13' a. m. and 8 h 27' p. m. ; for if any of 

 the observations is accidentally omitted at one of the hours, 

 the mean of the remainder will approach nearer to the mean 

 temperature of the year, than if any other two hours had been 

 taken, and similar omissions made. 



There is, however, another advantage of this determination, 

 namely, that the mean temperature of the year may be ob- 

 tained with great accuracy by a single observation made every 

 day at one of the times of mean temperature. 



If we examine the annual curve, and also the monthly curve, 

 it will be seen, that the ascending or morning branch is more 

 regular in its progression than the descending or evening- 

 branch. On this account, we would prefer a single observation 

 every day, made at the time of the morning mean, to a single 

 observation made every day at the time of the evening mean. 



It must be carefully observed, that the hours of mean tem- 

 perature which we have now been considering, are only mean 

 results for the whole year. If we wished to deduce the mean 

 monthly temperatures from an observation made once a-day, 

 it would not answer to take 9 h 13' a. m. and 8' 1 27' p. m. ; be- 

 cause the times of mean monthly temperature occur at dif- 

 ferent hours of the day throughout the year, as will appear 

 from the following table : 



