OBSERVATIONS ON THE MAGNETIC DIP AND DECLINATION. 333 
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Necdlearkedend|insurument| “elds [ofobservation,| "reads. || reads. | "of Needle, jy Attached. | Name 
of needle, of Needle, | H. M. [Peg-|Mins.g" venths.|Deg.|Mins.§Tenths, Deg,|Mins.§Tenths./ (Fahrenheit. Observer. 
1 N E E 2.0 pm.59.37.0 |59.20.0 |59.98.5 
«“ «“ WwW Ww 2.45 |57.38.0 |[58.05.0 (57.51.5 
«“ “ Ww E 3.10 59.00.0 (59.18.0 [59.09 
7 iL E Ww 3.25 68.15.0 [|58.00.0 [58.07.5 | 
Needle No. 1, with marked end south, gives. stag a 58° 29'.6 
Needle No. 1, with marked end north, gives. 2 1... 68 891 
Dip, by sixteen observations on needle No.1, . . . ... ja! G@r@ded 
Clear, pleasant weather all day. Pleasant breeze from south-east. Air humid. 
February 12th, at Dr. Everett’s house. 
2 Cr E | 10.20a.m/59.28.0 [59.03.0 [59.15.56 
e og W |10.55 (59.17.0 |59.45.0 [59.381.0 
“ “ Ww E {11.30 |58.22.0 |58.37.0 (58.29.5 
“ “ E |W [11.55 (59.30.0 |59.15.0 |59.292.5 
2 SU) Wo[ WY] 8.12 P.mj57.25.0 157. 00.0 + (57.12.5 de i 
“ “ E E 3.40 |58.33.0 [59.03.0 58. 48.0 
“ “ E Ww 57.10.0 (67.25.0 [67.17.5 
“ « Ww E 58.33.0 |58.22.0 [58.27.5 
Needle No. 2 gives, with marked end north, . . . . . . . 2. . 69° 09'.6 
Ribs DN 6 ea ee ee 
Dip, by sixteen observations on needle No.2, . >. .* ww... C88 88 
Dip, by sixteen observations on needle No.1, . ...... 2... 58 343 
Magnetic dip at Dr. Everett’s house, near the mouth of the river Sabine, 
by a mean of thirty-two observations, on both needles, . . . . . . 58° 33/.65 
February 17th, 1840. At Dr. Everett’s house, west shore of the river Sabine, near its 
entrance into the sea, Texas; Latitude 29° 43’ 54”, N.; Longitude 93° 51’ 30”, west 
of Greenwich. 
This night the star Polaris (a Urs Minoris) was observed upon at its greatest 
western elongation, in order to obtain the true meridian direction, to be used in observing 
the variation of the magnetic needle. 
The observation was made with a good transit theodolite, (marked No. 2) by E. Draper, 
of Philadelphia. 'To avoid any error in transferring the azimuthal direction of the star 
while at its point of greatest elongation, to the surface of the ground, an artificial horizon 
of quicksilver was used, and the azimuth-plate of the theodolite was so adjusted, by the 
levelling screws, as to cause the vertical wire to bisect the star and its reflected image by 
a vertical sweep of the telescope, made a few seconds before the time of greatest elonga- 
tion. 
When the observation on the star was completed, the telescope was carefully brought 
to a horizontal position, and a lantern was placed upon the ground at a distance of one 
hundred and forty yards to the north, and so adjusted in position as to be bisected by the 
vertical wire. A stake was driven firmly into the ground to mark this point, and ano- 
ther to mark the position of the centre of the theodolite. Next morning, (February 18th, ) 
the theodolite was adjusted carefully in its former position, and an angle of 1° 46’ 15" 
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