338 MR BLACKADDER on Meteorological Instruments 



versity of opinion as to the hours at which the indications of in- 

 struments ought to be noted ; and, consequently, the want of 

 correspondence between registers kept by different individuals, 

 the difficulty, or rather the utter impossibility, of deriving any 

 positive results from a comparison of these registers, must be 

 abundantly evident. The invention of a thermometer that re- 

 gisters accurately the highest and lowest temperatures that may 

 occur during a given period, was doubtless a great acquisition, 

 and such an instrument has been found of much use in many 

 highly interesting investigations. If, indeed, it were ascertained 

 that the mean of the highest and lowest temperatures of the day 

 was exactly equal, or bore a known and uniform relation to the 

 mean temperature of the whole day, then would such an instru- 

 ment be of great utility in determining the general and important 

 problem of mean temperature. This, however, has not yet been as- 

 certained, nor can such a problem be solved without much labour, 

 and an infinity of future observations. The result of some re- 

 cent observations would certainly lead to the conclusion, that the 

 mean of the extremes is not the mean of the daily temperature 

 in such countries as Britain, more especially at certain seasons of 

 the year, and in certain years, or series of years, less than in 

 others. 



It has been acknowledged, that the only way by which the 

 mean daily temperature can be determined with accuracy, is by 

 taking the mean of observations made frequently, and at least 

 once every hour, during the whole period of the day and night ; 

 and nothing but the hitherto extreme difficulty of putting such 

 a method into execution, has prevented its adoption. Some few 

 individuals acting in concert, and by turns, have persevered se- 

 veral weeks in registering the hourly indications of the thermo- 

 meter. But, little is to be expected from such exuberant zeal ; 

 and, even those most likely to engage in such undertakings, are 



