nnn : sn i Ee AN OT TTA i i 
OBSERVATIONS ON THE MAGNETIC DIP AND DECLINATION. 34] 
Norz.—The day was clear, with a very light north-east wind, and the atmosphere very dry. 
From the difference in latitude between Everett’s house, near the mouth of the river Sabine and Gaines’s 
Ferry, amounting as it does, to 1° 44’ 21”, it was supposed there would be found a considerable difference in the 
variation of the needle at these two places.—The results here reported show, however, no appreciable difference. 
On perceiving this, I was induced to apprehend there might have been some inadvertent error in the determination 
of the true meridian at the latter station. ‘The calculations were therefore received with care, and were found to 
give the correct deduction from the observations as recorded. 
Lieutenant Lee has full confidence in his observations for the determination of the true meridian at Gaines’s 
Ferry. For this purpose two separate sets of observations were made by him of the sun’s azimuth, at equal 
altitudes, a.m. and p.m., and the results coincided within thirteen seconds of arc. ‘There could have been no 
error in the magnetic bearing of the line indicated by the stakes placed by him to mark the true meridian, as the 
many observations with the different compasses used, would no doubt have detected such error. 
The determination of the true meridian at Everett’s house was done with every possible care, by observations 
on the star Polaris, verified by two different night’s observations, using, in both instances, an artificial horizon of 
quicksilver, and observing the azimuth of the star both direct and by reflection. 
VII. June 4th and 5th, 1840.—Observations on the dip of the needle, at a point about 
seven hundred feet north of Polvido’s house, near the left bank of Sabine River, 
Louisiana. Latitude 32° 01’ 01”, N.; Longitude 94° 00’ 00”, W. 
NEEDLE No. 1. 
iemat ont eee onmtemen: Dip obssbhed. | 
S June 4, 8 12h, 20m. P.M. 61° 20'.25 | 
N June 5, 8 11° 27 Aa G1? 67-75 
Dip, by sixteen observations on needle No. 1,. . . 61° 39.0 
Neepwe No. 2. | 
N June 5, 8 5h. 37m. P.M. 61° 53.4 iI 
S June 5, 8 6 32 61° 11.9 | 
Dip, by sixteen observations on needle No.2, . . . 61° 32'.6 
Dip, by sixteen observations on needle No. 1, 61° 39/.0 
By giving to needle No. 1 twice the weight of No. 2, we get the following result for 
the dip at this station, viz: 
W0.1,.e O17 00x wy edie ae iH 
No. 2, = 61° 32°6 x 1, = 61° 32'.6 il 
Bim,  %. 20, .. Fo...80\, 14oBOLE | 
Which, divided by 8, gives 61° 36’.8 for the magnetic dip at this station on the 4th 
! 
and 5th of June, 1840, | 
Notr.——The point of observation is N. 70° E., (compared with the ¢rwe meridian,) and is distant two and a i} 
half miles from the intersection of the river Sabine with the 32° of north latitude. i} 
Olear, calm, very hot and dry weather, during the observations. 
VILL. Nachitoches, Louisiana. 
June 26, 1840,.—Observations on the dip of the needle, made in the small summer- 
house in Mr. Ochmichen’s garden. 
