40 THE EEGISTEE. 



only means for the observer to give its true value to his labor, is 

 to make the corrections, the reductions, and the calculations of 

 the means himself. It is for want of having thus been elaborated 

 that voluminous collections of observations, the fruits of long 

 years of toil, remain useless and forgotten in the dust of libra- 

 ries, because the meteorologist finds it impossible to make use of 

 them without first undertaking those calculations, the amount of 

 which absolutely transcends the powers of an individual, and 

 would discourage the most ardent zeal, while they would have 

 cost the observer only an instant each day, if he had made them 

 at the time of the observations. 



The calculations desirable are as follows : — 



1. Each barometrical observation must be reduced immediately 

 to the temperature of zero Centigrade, or 32° Fahrenheit, by 

 means of the tables, and the total correction of the barometer, if 

 there is any, will be applied. 



2. The diurnal means of the several instruments, resulting from 

 the sum of the three observations made at these diflerent hours, 

 divided by three, must be entered each day in the respective 

 columns, after the observation of 9 p. m. It is needless to say 

 that these means should be drawn solely from observations re- 

 duced and corrected. 



3. The monthly means for each hour separately — that is, the 

 monthly mean of the observations of 7 a. m., and that of 2 p. m., 

 and of the observations of 9 p. m. 



4. The monthly means drawn from the means of each day; the 

 monthly extremes of the instruments; the monthly amount of the 

 rain, hail, or snow; the mean cloudiness of the sky ; the prevail- 

 ing wind, &c. 



5. The annual means and amounts, and the respective extremes 

 for the civil year. 



It will be interesting to calculate, also, if the observer is so 

 disposed, the mean of the seasons of the meteorological year, 

 which begins December 1, to November 30, of the following 

 civil year. 



The meteorological seasons are, then : — 



Winter — December, January, February. 



Spring — March, April, May. 



Summer — June, July, August. 



Autumn — September, October, November. 



