— 
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° 
2 39” East variation. 
The following were copied from the returns made to the Trea- 
sury department by the public surveyors. 
. Mouth of the Scioto, - - variation 5° EE. in 1805. 
Augusta, on the Ohio, = - - s 5 -E... 1806, 
Jeffersonville, - - a: . 45’ BE. sé 
Natchez, . E. 1802. 
In Louisiana, lat. 310, fone 90 10 W. varia. ; 20E. 1807. 
ashe Washita river, lat. 34°, lon. about 920 W.8 20E. ¥*1804. 
Amelia Island, lat. 30° 44’, long. 81920°W. 2 W. = 1775. 
Mouth of St. rales lat. 45° 5’, long. 67° 12’, 12 19W. = 1797. 
Pensacola, lat. 30° 25’, long. 87° 12’ W. 430E. 1780. 
Port Royal, S. C. long. 79° 30’ - os Bi: i Aes. 
Charleston, S. C. - - «. § 48.4. d0d4. 
Nantucket, - . - - ~.. 6.30 W,: +1776. 
Plymouth, — - - - Cpe See eee vets 
Boston Harbor, = - - - <=.) FD We. 1576. 
Penobscot Bay, - - - a 
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, Vol. I, page 43, are given some 
more observations. In Samuel Williams’s History of Vermont, 
2d edition, 1809, is given a table of all the magnetic observations 
*By William Dunbar. 
