340 OBSERVATIONS ON THE MAGNETIC DIP AND DECLINATION. 
VI. May 29th, 1840,—At Gaines’s Ferry, west bank of the Sabine river; Texas. 
Latitude 31° 28’ 15”, N.; Longitude 93° 44’ 33”, W. Same station as V. 
Magnetic bearing of a true meridian line established by equal altitudes of the sun, to 
ascertain the variation of the magnetic needle.* 
1. By compass No. 3, needle six inches long. Poles of needle direct. 
A mean of six observations made as heretofore described, gives, . . . 8° 35.5 KE. 
Mean time of observation, 9/. 05m., A.M. 
Poles of needle reversed. A mean of six observations made as’ heretofore 
described, gives . . ' ms tartan -finte: taxee dines stan 
Mean time of sbeurelien 10h. Abin A. M. 
Magnetic variation by twelve observations on the needle of compass No. 3, 8° 36’ E. 
2. By compass No. 4, needle five and a quarter inches long. Poles of 
needle direct. A mean of six observations made as heretofore described, 
give, . ore cop ye ee eS 8. 46.6 B. 
Mean time of Sbecttetian: oh. oO A.M. 
Poles reversed. A mean of six readings made as heretofore described, gives, 8° 44’.6 
Mean time of observation, 11h. 05m. a.m. 
Magnetic variation by twelve observations on needle of compass No.4,. . 8° 45’ E. 
By the compass belonging to the Texan commissioner; needle six inches long. 
A mean of six observations made as heretofore described, . . . . . . 8° 40'.6 
Mean time of observation, 11h. 20m. A.M. 
This needle could not conveniently be taken out of its box, and its poles were not 
therefore reversed. 
SUMMARY. 
1. Variation of the needle of compass No. 3, of six inches long, by a mean 
of twelve observations, . . .. ; By ave Bei8G) Ts 
2. Variation of the needle of compass No. A, “of fe and a Lil ee 
long, by a mean of twelve observations . . . ..-:.. . + . 846! 
3. Variation of the needle of the Texan commissioner’s compass, of six 
inches long, by a mean of six observations, . . ren BSd0R6 
Magnetic variation at Gaines’s Ferry, Texas, in lativide 31° ‘28! 15", N.; 
and longitude 93° 44’ 33”, W.; by a mean of thirty observations on three 
needles, on the 29th of May, a LG, 
«This true meridian line was fixed by my principal assistant, Lieutenant T. J. Lee, of the corps of topographi- 
eal engineers, on the 10th of May, 1840, before my arrival at Gaines’s Ferry. It was done by observing the 
©’s azimuth, at equal altitudes, a.m. and P.™., and correcting for the effect of the change of declination during 
the interval. ‘Two stakes were driven to indicate the true meridian direction. ‘The magnetic bearing of this line 
was observed by me with the several needles, as indicated. 
