Variation and Dip of the Magnetic Needle. 295 



Nearly all of the foregoing observations have been made within 

 the four or five last years (from 1810.) They go to the estab- 

 lishment of a principle which will be found of considerable use 

 to surveyors, viz. that the quantity of variation easterly in the 

 same parallel, increases gradually and nearly equally in advancing 

 westward at the rate of a degree in about 60 English miles." 



Mr. Edward Livingston states that the first observation made in 

 Louisiana by Father Laval, in 1720, determined the variation at 

 New Orleans to be 2° E. ; and that by sixty-two observations 

 made by Lason in 1806, who employed in each six different nee- 

 dles, which made 372 observations, he had found a mean of 8° 

 %' 39'^ East variation. 



The following were copied from the returns made to the Trea- 

 sury department by the pubhc surveyors. 



Mouth of the Scioto, - - variation 5° E. in 1805, 



Augusta, on the Ohio, - - " 5 E. 1805. 



Jefferson ville, - - " 6 45^E. " 



Natchez, - - - " 9 E. 1802. 



In Louisiana, lat. 31^, long. 92° 10' W., varia. 9 20 E. 1807. 



On the Washita river, lat. 34°, Ion. about 92° W. 8 20 E. *1804. 



Ameha Island, lat. 30° 44', long. 81° 20' W. 2 W. 1775. 



Mouth of St. Croix, lat. 45° 5', long. 67° 12', 12 19 W. 1797. 



Pensacola, lat. 30° 25', long. 87° 12' W. 4 30 E. 1780. 



Port Royal, S.C. long. 79° 30' - - 3 E. 1777. 



Charleston, S. C. - - - 3 48 E. 1777. 



Nantucket, - - - - 6 30 W. 1776. 



Plymouth, - - - - 7 W. 1776. 



Boston Harbor, - - - . - 7 40 W. 1776. 

 Penobscot Bay, - - - - 9 W. 



Besides the preceding observations, few of which have ever 

 been published, I have endeavored to collect together all the pub- 

 lished observations I could find. In Douglass' History of the 

 British Settlements in America, Vol. I, pages 270-2, is given the 

 variation for several places in the United States; and in Kalm's 

 Travels in North America, Yol. T, page 43, are given some 

 more observations. In Samuel Williams's History of Yermont, 

 2d edition, ] 809, is given a table of all the magnetic obser\^ations 



*By William Dunbar. 



