210 THE MAGNETIC DECLINATION IN CALVERT COUNTY 



fence. Station 28B is the north monument of this meridian line and 

 is about 200 feet north of the south stone. 



For a description of the methods and instruments used, reference 

 must be made to the " First Eeport upon Magnetic Work in Maryland," 

 vol. i, Maryland Geological Survey Eeport. This report gives likewise 

 an historical account of the phenomena of the compass-needle and 

 discusses fully the difficulties encountered by the surveyor on account 

 of the many fluctuations to which the compass-needle is subject. In the 

 Second Eeport (Md. Geol. Survey, vol. v, pt. 1, 1905), the various values 

 observed in Maryland have been collected and reduced. Surveyors of the 

 county desiring these reports, should address the State Geologist. 



MERIDIAN LINE. 



On June 25, 1900, Mr. J. B. Baylor, acting under instructions of 

 the Superintendent of the United States Coast and Geodetic Survey 

 as issued to him, in response to a request from the State Geologist 

 established a true meridian line at Prince Frederick in the Court-house 

 Square. This line is marked by two substantial monuments, suitably 

 lettered and firmly planted in the ground. (See description above.) 



The Stone which is best removed erom all disturbing influ- 

 ences, SHOULD BE THE ONE TO BE USED BY SURVEYORS WHEN MAKING 

 THEIR TESTS. 



When the surveyor determines the value of the magnetic declination, 

 it would be well for him to make the observations on several days, if 

 possible. Probably the best time of day for making the observations 

 would be towards evening, about 5 or 6 o'clock.^ At this time the 

 declination reaches, approximately, its mean value for the day (see 

 Table II). The observations on any one day should extend over at least 

 one-half of an hour, preferably an hour, and the readings should be taken 

 every ten minutes. Before each reading of the needle it would be well 



' Or the surveyor may make his observations in the morning and early 

 in the afternoon, at about the time of minimum and maximum values of the 

 magnetic declination. He may regard the mean of the two extreme values 

 as corresponding closely to the mean value for the day (24 hours). 



