182 



THE 3IAGXETIC DECLINATION IN ST. MART'S COUNTY 



This table shows that during August, for example, the magnetic de- 

 clination has its lowest value abont S a. m. and its highest value at about 

 1 r. M., and that lietwcen 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 Leonard- 

 town between 1700 and 1905. 



From this table it will l)e noticed that the needle is at the present time 

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



TABLE III. 



ago, and that in about 1805-10 the magnetic declination had its lowest 

 value of about 25' west, after which it began to increase again. In about 

 a century, since 1805, the compass has. accordingly, changed its direction 

 about 4f °. 



A street a mile long, laid out in Leonardtown in 1805 to run north unci 

 soxdli by ilie comijasx. icould. at the present iime (190-5), 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 in the magnetic declination or pointing of the compass between 

 any two dates between 1700 and 1900. It should be emphasized, how- 

 ever, that when applying the c|uantitics thus found in the re-running 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 com- 

 pass used in the original surve3\ 



