LINES OF MAGNETIC DECLINATION IN THE ATLANTIC. 
177 
22. Observations at several stations in Guiana in 1842 and 1843, by Sir Robert 
S cHOMBURGK, employed as Boundary Commissioner; MSS. 
23. Observations at several stations in the vicinity of the River St. Lawrence in 
1842, by Captain J. H. Lefroy, R.A. ; MSS. 
24. Observations at several stations in the British Islands in 1838, by Captain 
Sir James Clark Ross, R.N. ; MSS. 
25. Observations (with a transportable Declinometer) at stations on the North 
Coast of Scotland, by Commander H. C. Otter, R.K. ; MSS. 
26. Observations at several points of the coast of Western Africa in 1845 and 1846, 
by Captain H. M. Denham, R.N. ; MSS. 
27 . Observations at several stations on the coast of the United States of America 
in the years 1844 to 1846, in the progress of the United States Coast Survey; extracted 
from the published Charts of the Survey. 
28. Observations (with a transportable Declinometer) in 1848 at stations in the 
Gulf of St. Lawrence, by Dr. Kelly, R.N. ; MSS. 
29. Declinations determined at the observatories of Algiers, Brussels, Cape of Good 
Hope, Christiania, Dublin, Greenwich, Makerstoun, Paris, St. Helena, and Toronto in 
Canada ; extracted from official sources : and at Rio Janeiro by Herr von Helm- 
reicher in 1845 with a transportable Magnetometer; MSS. 
30. Declinations observed by Lieut.-Colonel Graham of the United States Topo- 
graphical Engineers, and by other officers of that corps, and surveyors employed 
under his direction in the Commission for determining the boundary between the 
United States and the British Possessions in North America. I am indebted to the 
liberality and kindness of Lieut.-Colonel Graham for the communication of the ma- 
nuscript of these valuable observations, which connect the determinations of Captains 
Bayfield, R.N., and Lefroy, R.A. in Canada, with those of the United States Coast 
Survey in New York and the more southern states. 
Correction of the observations in Schedule (B.) for the effects of the Ship's Iron. 
Observations in H.M.S. Erebus on her passage from England to St. Helena and 
the Cape of Good Hope. 
When commenting in the Fifth Number of the Magnetic Contributions upon a 
portion of the magnetic observations of the two first years of Sir James Ross’s Ant- 
arctic Expedition, which were all that at that time had reached England, I remarked 
that their examination had led me to the opinion, that the disturbances of the compass 
in the Erebus and Terror exhibited a character distinct from any which had been 
previously recognised, either in theoretical discussions or in practical applications. 
In all the investigations with which I was acquainted, in which the disturbing influ- 
ence of a ship’s magnetism upon her compass had been considered, and in all the 
remedies which had been suggested, either by the employment of counteracting 
forces, or by corrections to be applied to the indications of a compass where no such 
