MAGNETIC OBSERVATIONS. fj 



St. Thomas, West Indies. The ship -was swung in this harbor, on November lSth, 

 1865, in the usual manner. Her position at the time was hit. 18° 19' N., long. 

 64° 56' W. Joint XII on the after turret was 14.4 inches to port. 



The observations on shore were made in Long Bay, at a spot about thirty feet 

 from the water's edge, on a gravelly beach, to the eastward of the town. From 

 the place where the instruments stood the true bearing of Fort Cowell, at the en- 

 trance to the harbor, is S. 34° 50' W., and it is distant about one mile. 



Assuming the position of Fort Christian to be hit. 18° 20' 27" N., long. 4 h 19 m 

 42 9 .7 W., then, according to the English Admiralty Chart, the position of the spot 

 where the instruments were set up is 



Lat. 18° 20' 22" N. 

 Long. 4 h 19"' 40.6 W. 



Isle Royal, Salute Islands. An attempt was made to swing the ship here, on 

 November 30th, 1865, in the usual manner, but it failed on account of the continual 

 rain which shut off the view of the distant azimuth mark. The position of the 

 ship at the time was lat. 5° 17' N., long. 52° 33' W. Joint XII on the after turret 

 was 0.6 of an inch to starboard. 



The magnetic and astronomical observations on shore were made on the south- 

 west side of the island, at a spot from which the corner made by the southeast and 

 southwest faces of the government coal sheds bears N. 64° W. (true), and is distant 

 one hundred and thirty-two feet. The place was examined carefully for local 

 attraction by taking fore and back sights with a compass, but none could be 

 detected. The position occupied by the instruments is in 



Lat. 5° 17' 29" N. 

 Long. 3 h 30 m 1P.4W. 



The latitude was determined from a single set of circummeridian altitudes of the 

 sun observed by me, and the longitude was taken from the French chart. 



Ceara, Brazil. An attempt was made to swing the ship here, on December 

 19th, 1865, in the usual manner, but although a very favorable opportunity was 

 chosen, she could only be made to turn through ten points. Her position at the 

 time was lat. 3° 44' S., long. 38° 34' W. Joint XII on the after turret was 0.6 

 of an inch to starboard. The wind, current, and sea are so strong here that vessels 

 at anchor in the roads always ride with their heads nearly in the same direction, 

 never swinging more than about three points. 



At this place there is no harbor whatever, merely an open roadstead. A heavy 

 surf is constantly running on the beach, and as there are almost no facilities for 

 landing in small boats, getting the instruments on shore involved a good deal 

 of trouble and some risk. However, I succeeded in landing them safely, and 

 obtained a very good set of observations on the white sand beach at a spot about 

 one hundred and fifty feet from the water's edge, and from which the true bear- 

 ing of the southeast corner of the custom-house on the wharf is N. 53° 19' W., 

 and its distance two hundred feet. From the same spot the true bearing of 



