TRANSACTIONS OF THE SECTIONS. 13 



tigations." Referring, more particularly, to his paper of last session On the Loss 

 of the Tayleur, and to the principles on which the lines of magnetic force, and the 

 equatorial, or neutral plane, are adjusted in correspondency with the earth's polar 

 magnetic axis,— it followed, he showed, that the distribution of the magnetic lines 

 externally should have special relation to the direction of the ship's head whilst 

 building, and should therefore be easily predicted, proximately, for every particular 

 case. 



The views of Dr. Scoresby on these fundamental principles, as well as on the 

 source of and changes in the more intense quality of magnetism, the retentive, in 

 iron ships, had had very extensive and beautiful verifications in actual experi- 

 ments, since the former meeting of the Association. As to the equatorial plane of 

 no-attraction, illustrated by diagrams in " Magnetical Investigations," which were 

 cut in wood in the year 1851, — experiments in 1854 and 1855, on five or six ships 

 whilst yet on the stocks, had shown the most remarkable correspondency. Thus, 

 in the case of the Elisabeth Harrison, at Liverpool, having her head about E.N.E., 

 which Dr. Scoresby examined in October 1854, — the plane of no- attraction on the 

 starboard side was found to lie 11 feet 6 inches lower than that on the port side, 

 whilst the difference, previously calculated, according to theory, was 11 feet! In 

 the case, again, of the Fiery Cross, of Glasgow, investigated at his request by Mr. 

 James Napier, the lines of no-attraction on the two sides, with the ship's head 

 S.W.erly, were found to be almost exactly in agreement with theory. Again, in the 

 case of the Elba of Newcastle, built at Jarrow on Tyne, with her head only half a 

 point from the magnetic meridian ; as also of another ship built on the same spot, 

 the magnetic lines were found in close analogy with those figured in the diagrams 

 above referred to. Finally, in the case of the Persia, a large and splendid ship 

 built by Messrs. Napier and Co., at Glasgovi', the magnetic lines, as determined by 

 Mr. James Napier, were found to have the like conformableness with theoretic 

 deduction. One striking and beautiful exception — beautiful because anticipated on 

 magnetic principles — was brought out In experiments made by Mr. Robert Newall, 

 Mr. George Palmer, and Mr. James Napier. This apparent exception consisted in 

 certain irregularities in the external lines of the magnetic plane, — sometimes shown 

 in sudden limited deflections, — a circumstance plainly referable to particular accu- 

 mulations of iron material within, such as of beam ends, stringers, bulk-heads, &c., 

 which the author had noticed in his " Magnetical Investigations" as not unlikely 

 to disturb the regularity of the magnetic lines. In this case, therefore, the observed 

 exception to regularity served most convincingly to confirm the general rule. 



Dr. Scoresby then proceeded to show how mechanical action, such as vibration, 

 straining, or blows of the sea, on an iron ship, must modify or change the original 

 magnetic lines, and tend (whatever the extent might practically be) to bring them 

 into some measure of conformity with the terrestrial magnetic force as applied to 

 the new direction of the ship's head. 



One case of positive and demonstrable change in the magnetic lines of a new 

 ship, the Imperador, built at Liverpool, Dr. Scoresby had experimentally deter- 

 mined ; a change which had taken place (in exact conformity with his predictions) 

 whilst the ship was being fitted out for sea. In this instance the lines of no-attrac- 

 tion on the two sides of the ship, which from her position on the stocks must have 

 originally differed some 10 feet in level, were found to have changed to within 

 about 20 inches of the same level. This showed, as the general experience of the 

 adjusters of compasses and observant navigators also indicated, that much service 

 at sea, and well knocking about on various courses, had the tendency to bring the 

 original extreme and oblique magnetic lines into a normal direction, — approaching 

 to a horizontal equatorial plane with lines of no-deviation running on both sides, 

 nearly on the same level, from stem to stern, and a polar axis (in the centre of the 

 ship) vertical to the keel. This tendency was elucidated by different striking facts 

 of experience. 



The author further explained, and illustrated by bold and descriptive drawings, 

 several cases of sudden and remarkable compass-changes, dwelling particularly on 

 that of the Tayleur, where a change of some points had taken place within two or 

 thiee days, whilst contending against a heavy sea with her head in a reverse po- 

 sition from that on the stocks ; and on that of the Ottawa, one of whose compasses 



