150 



THE CLIMATE OF ST. MARYS COUNTY 



in Janviary and rebruan-, an entirely erroneous conclusion ; for by 

 comparing the Baltimore and Solomons records for the same period 

 of years, the proper relation of temperature for the two stations becomes 

 at once apparent.' 



Mean temperatures for short periods may, however, be corrected, when 

 there is available for comparison a long record at a station not far 

 distant, and similarly located with respect to its topographic surround- 

 ings. For Lament has shown that in spite of the variability of the 

 temperatures from month to month, the differences between neighboring 

 places remain constant. These differences are fixed by physical causes 

 and so may be strictly considered a meteorological constant (Hann). 

 Baltimore is not very differently situated from other stations in southern 

 Maryland, and its record for 88 years may be used as the criterion by 

 which to ascertain the corrections to be applied to short term records 

 to obtain the true normals. The application of the method may be 

 conveniently illustrated by an example. 



The January mean temperature at Baltimore (88 years) is 34.9° ; the 

 January mean for Charlotte Hall (10 years) is 34.0°. Charlotte Hall 

 is 56 miles south of Baltimore, and cannot normally have a lower mean 

 winter temperature than Baltimore. The correction to be applied is 

 calculated as follows: 



Charlotte Hall.. 



Departures ■ 



Baltimore 



Difference-... 



Departures . 



0.0 



0.2 



-0.9 



0.4 



1899 1900 1901 1902 1904 Means, 



0.3 



-0.2 



-1.1 



1.2 



" Difference between Charlotte Hall and Baltimore. This first column of departures 

 is the departure from the average of the mean temperatures ; the last column of 

 departures is the departure from the normal of the differences between Baltimore and 

 Charlotte Hall. 



The average of the variations of actual mean temperatures at Charlotte 

 Hall is 2.2°, with a probable error for the 10-year period of plus or 

 minus 0.6° ; but the average of the variations in the differences between 



' See the chapter on climate in Calvert County Report. 



