212 



THE MAGNETIC DECLINATION IN CALVERT COUNTY 



declination has its lowest value about 8 a. m. and its highest value at 

 about 1 p. m., and that between these two hours the needle changes its 

 direction about 10', which amounts to 15 feet per mile. In winter the 

 change is considerably less. 



Table III shows how the magnetic declination has changed at Prince 

 Frederick between 1700 and 1905. 



TABLE TIL 



From this table it will be noticed that the needle is at the present 

 time pointing about the same amount to the west that it did two 

 centuries ago, and that in about 1805 the magnetic declination had its 

 lowest value of about -18' west, after which it began to increase again. 

 In about a century, since 1805, the compass has accordingly changed its 

 direction by about 4f°. 



A street a mile long, laid out in Prince Frederich in 1805 to run north 

 and south hy the compass, ivoidd, at the present time, have its north 

 terminus about 1/12 of a mile too far east! 



The above table enables the surveyor to ascertain the precise amount 

 of change of the magnetic declination or pointing of the compass 

 for any two dates between 1700 and 1905. It should be emphasized 

 however, that when applying the quantities thus found in the re-runiiing 

 of old lines, the surveyor should not forget that the table cannot attempt 

 to give the correction to be allowed on account of the error of the 

 compass used in the original survey. 



