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XVI. Report of Magnetic Experiments tried on Board an Iron Steam-Vessel , by 
Order of the Right Honourable the Lords Commissioners of the Admiralty . By 
Edward J. Johnson, Esq. Commander R.N. Accompanied by Plans of the Vessel, 
and Tables showing the Horizontal Defection of the Magnetic Needle at different 
Positions on board, together with the Dip and Magnetic Intensity observed at those 
Positions, and, compared with Observations made onshore with the same Instruments. 
Addressed to Charles Wood, Esq. M.P. 8s c. 8$c., and communicated by Captain 
Beaufort, R.N. F.R.S. Hydrographer to the Admiralty , by Command of the 
Right Honourable the Lords Commissioners of the Admiralty . 
Received February 16, — Read March 10, 1836. 
London, January 16th, 1836. 
Sir, — In pursuance of orders from the Lords Commissioners of the Admiralty, I 
proceeded to Ireland, taking with me the necessary instruments for ascertaining the 
deviation of the magnetic needle produced by the local attraction of an iron steam- 
vessel, together with others for determining the dip, magnetic intensity, &c. 
Every facility for pursuing the inquiry directed by Their Lordships was afforded by 
Messrs. Laird, of Liverpool, who built the “ Garryowen and the City of Dublin 
Steam Packet Company (through Charles W. Williams, Esq.) liberally offered the 
use of the above-named vessel, on the river Shannon, for the purpose of trying the 
necessary experiments ; and I must not omit to mention in this place my obligation 
to Professor Barlow, from whom I received many valuable hints relative to the ap- 
plication of his correcting-plate previous to leaving London. 
With a view to perspicuity I have divided the accompanying Report into sections. 
§ 1 . Description of the Method of Investigation. 
There being no wet dock at Limerick, nor in its vicinity, suitable for swinging the 
Garryowen, she was put under my directions inTarbert Bay, on the 19th of October, 
and the following method of investigation was pursued. 
All the compasses intended for use were carefully examined, and the caution of 
removing all iron from the person during the observations was strictly attended to. 
Having fixed a station (X) on the south-west side of Tarbert Bay, a mile distant 
from the vessel, from whence the cone of a very remarkable mountain* in the County 
of Clare, and distant about nineteen miles, could be distinctly seen. I observed the 
* “ Dicomede.” 
2 m 2 
