MARYLAND GEOLOGICAL SURVEY 151 



the Baltimore and Charlotte Hall means is only 0.1°, or twenty times 

 less, and the probable error is only plus or minus 0.03°. As the mean 

 for January at Baltimore for 88 years is 34.9°, and Charlotte Hall is 

 normally 1.3° warmer (probable error 0.03°) the corrected January 

 mean for Charlotte Hall is 34.9° plus 1.2°, which is equal to 36.1°. The 

 corrected mean temperatures given in Table I have all been ascertained 

 in this way. 



In order to secure a fairly accurate mean temperature for St. Mary's 

 County, the corrected means for the following stations have been em- 

 ployed, viz.: Charlotte Hall (9 years' record) situated in the northwest 

 portion of the county, Cherryfields (5 years), St. Mary's (7 years), and 

 St. Inigoes (7 years) in the southern portion of the county, and 

 Solomons (14 years) near the middle of the northern shore. 



The Temperature Conditions. 



The average monthly and annual mean temperatures corrected as 

 indicated are given in the second part of Table I. The upper portion 

 of the table contains the original uncorrected data for all stations in 

 the county. The annual mean temperature for St. Mary's County is 

 found to be 57.1°. This is slightly higher (0.3°) than the mean for 

 Calvert County. Spring (55°) and autumn (59°) have the same tem- 

 perature as Calvert County, but summer (76°) is about a degree cooler, 

 and winter (38°) a degree warmer, a difference wliich may be attributed 

 to the superior influence of the Bay. The warmest month is July, with 

 a mean of 78°, and the coldest January, with 37°, giving an annual 

 range of 41°. The extremes in St. Mary's County are, maximum 104° 

 at Eidge in July, 1856, and minimum 19° below zero at Charlotte Hall 

 in February, 1899.'' The range in absolute temperatures is 123°. 

 Maximum temperatures of 100° or above have also been recorded at 

 Charlotte Hall and St. Inigoes, and 2° below zero occurred at Leonard- 

 town during the cold winter of 1893. 



The monthly mean temperatures at all stations are given in Tables II, 

 III, IV, V, VI, VII, and XV. 



' See the remarks in regard to this record on page 168. 



