207 



N. Y., on llie 24lh of August, 1840. Its place was afterwards sub- 

 stituted by two other needles, marked No. 3 and No. 4. They were 

 made expressly for Major Graham, by Mr. J. M. Baur, of New York, 

 and are of the acute lozenge shape, very similar in form to No. 2. 



The needles were always charged as strongly as practicable, and 

 generally to saturation, both when the poles were direct, and also 

 when reversed. This is an important object in observing the dip, for 

 the stronger the needles are charged with magnetism, the less is the 

 effect of any want of perfect balance, or any imperceptible dust, or 

 other particles which may adhere to them, to deflect them from the 

 true angles of dip. 



The localities occupied by the instrument, at the several stations, 

 have been minutely described in the memoir, in order that they may 

 be easily found by future observers, and that an exact comparison of 

 results may be made, and the change of dip, with the lapse of time, 

 be the more accurately ascertained. 



The following are results obtained by Major Graham: 

 At the light-house, at the S. W. pass, mouth of the Mississippi 

 river. Lat. 28° 58' 50" N., Long. 89° 21' 27" W. 



On the 29th January, 1840. Dip 58° 42'.25. 

 At Dr. Everett's house, near the mouth of the River Sabine, Texas. 

 Lat. 29° 43' 54" N., Long. 93° 51' 30" W. 



On the 11th February, 1840, Dip 58° 33'.65. 



On the 28th February, 1840, Dip 58° 32'.1. 



On the 19th February, 1840, Declination 8° 40'. 1 E. 

 On the 29th February, 1840, Declination 8° 40'. 3 E. 

 At Gaines' Ferry, on Sabine river, Texas. Lat. 31° 28' 15'' N., 

 Long. 93° 44' 31" VV. 



On the 28th and 29th May, 1840, Dip 60° 57'. 



On the 29th May, 1840, Declination 8° 40'.5 E. 



At Polvido's house, on Sabine river. La. Lat. 32° 01' 01" N., 

 Long. 94° W. 



On the 4th and 5th June, 1840, Dip 61° 36'.S. 

 At Natchitoches, La. 



On the 26th June, 1840, Dip 61° 15.'9. 

 At West Point, N. Y. Lat. 41° 23' 25" N., Long. 74° 01' W. 



On the 24th August, 1840, Dip 73° 20'.09. 



At a point 4578 feet due north from the monument at the source 



of the river St. Croix. Lat. 45° 57' 23".6 N., Long. 67° 46' 45" W. 



On the 18th, 19th and 20th Oct. 1840, Dip 76° 57'.4. 



At Parke's Hill. Lat. 46° 06' 40" N., Long. 67° 46' 45" W. 



On the 27th, 28th and 29th Nov. 1840, Dip 77° 02'.5. 



