548 Royal Society. 
-‘rizontal deflection of the Magnetic Needle at different positions on 
board, together with the dip and magnetic intensity observed at those 
positions, and compared with that obtained on shore with the same 
instruments. Communicated by Captain Beaufort, R.N., F.R.S., 
Hydrographer to the Admiralty; by command of the Right Hon. the 
Lords Commissioners of the Admiralty. 
This report commences with a description of the iron steam-vessel, 
the “ Garryowen,” belonging to the City of Dublin Steam Packet 
Company, and built by the Messrs. Laird, of Liverpool. She is con- 
structed of malleable iron, is 281 tons burthen, and draws only 54 
feet water, although the weight of iron in the hull, machinery, &c. 
is 180 tons. 
This vessel was placed under the directions of the author, in Tar- 
bert Bay, on the Shannon, on the 19th of October, 1835, for the pur- 
pose of investigating its local attractions on the compass. The me- 
thods which were adopted with that view are given ; together with 
tables of the results of the several experiments, and plans of the va- 
tious parts of the Garryowen. The horizontal deflections of the 
magnetic needle at different situations in the vessel were observed, 
for the purpose of ascertaining the most advantageous place for a 
steering compass, and also for the application of Professor Barlow’s 
correcting plate: and the dip and intensity in these situations were, 
at the same time, noted. 
An experiment is detailed, showing that where several magnetic 
needles, freely suspended, were placed upon the quay, in Tarbert 
Bay, and the vessel warped from the anchorage towards them, first 
with her head in that direction and then with her stern, opposite de- 
flections were produced: in the first case all the needles showing a 
deviation to the eastward, and in the latter to the westward, of the 
true magnetic meridian. 
Considering the height of the general mass of iron in the vessel 
and also that of the head and stern, together with the distance (169 
feet) at which some of the needles indicated a deviation, the author 
concludes that the respective deflections were caused by the magnetic 
influence of the iron in the vessel ; the combined effect of that about 
the bows representing the north pole of a magnet, and that about 
the stern a south pole. Hethen offers several suggestions for future 
observation on this subject, and connected with the little oxidation 
that is reported to have taken place in the vessel. 
The experiments having been interrupted by a continuance of wet 
and stormy weather, the author proceeds to draw the following gene- 
ral practical conclusions, deduced from the series of observations 
already made, and points out the further experiments which he con- 
siders necessary to be tried. 
Ist. The ordinary place for a steering-compass on board ship is 
not a proper position for it in an iron steam-vessel. 
2nd. The binnacle-compass in its usual place on board the Garry- 
owen is too much in error to be depended upon. 
3rd. In selecting a proper position for a steering-compass on board 
iron steam-vessels, attention should be paid to its being placed, as 
