653 



TABLES 



FOR REDUCING THE MONTHLY AND YEARLY MEANS OF SINGLE YEARS TO THE 

 MEANS DERIVED FROM A SERIES OF YEARS. 



OBSERVATION shows that the monthly and annual mean temperature of a place 

 omewhat varies from year to year. No law, however, has been as yet discovered 

 s to the course of these oscillations. It follows that the means derived from observa- 

 tions carried on during a single year are but approximations to the true means. 

 ^These last must be obtained from observations made for a series of years, during 

 which these irregular variations become insensible by compensating each other ; and 

 it is obvious that their accuracy increases with the number of years which compose 

 the series. 



Professor Dove, having proved by his researches that these abnormal temperatures 

 above and below the average of a whole month, or of a year, are apt to be felt simul- 

 taneously on extensive tracts of country, concluded that the means of a single year 

 could be made available for obtaining the true means of the place, by being corrected 

 for the non-periodic variations by means of normal stations in the same meteorological 

 region, in which those elements had been more accurately determined by the obser- 

 vations of a long series of years. Comparing, namely, the means of a given year 

 with the means derived from the whole series, we find a difference in -|- or , which, 

 applied, with reverse signs, to the means of the same year in the neighboring station 

 to be corrected, will reduce, with a good degree of probability, the means of that 

 particular year to the means which would have been obtained from a long series of 

 years similar to that of the normal station. 



The following tables, LXXIX. to XCVIL, have been selected from those given by 

 Dove in his five papers on the non-periodic variations of the atmospheric tempera- 

 ture, to be found in the Memoirs of the Academy of Sciences of Berlin for the years 

 1838, 1839, 1842, 1848, and 1853, to which we must refer for further details. They 

 furnish normal stations for various latitudes ; the columns contain the corrections for 

 every month, viz. the differences, with reverse signs, between the monthly means in 

 the year indicated in the first and last columns, and the means derived from the 

 whole series, which are contained in the line at the bottom. 



