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XX. Reduction and Discussion of the Deviations of the Compass observed on hoard of all 
the Iron-huilt Ships, and a selection of the Wood-built Steamships in Her Majesty's 
Navy, and the Iron Steamship ‘ Great Eastern ; being a Report to the Hydrographer 
of the Admiralty. By Feedeeice J. Evans, Esg., Master R.N, Superintendent of 
the Compass Department of Her Majesty s Navy. Communicated by Captain Wash- 
ington, R.N., F.R.S., by command of the Lords Commissioners of the Admiralty. 
Eeceived May 5, — Eead June 21, 1860. 
SlE, London, April 18, 1860. 
In compliance with the general instructions I received from you on my appointment, to 
observe carefully the working of the Mariner’s Compass in the ships of Her Majesty’s 
Navy, and especially in iron vessels, both for the security of then navigation and the aid 
of science, I now beg leave to submit for your consideration the following Report 
treating on these points, and in which is embodied an analysis of the magnetic character 
of all the iron-built ships in Her Majesty’s Navy, as also of several of the wood-built 
steam-ships. 
In directing attention to this analysis, as given in a series of Tables, it is necessary to 
advert to the observations on which it is based, as resulting from a general system 
pursued in the Royal Navy. 
On the foundation of the Compass Department in 1843, a periodical examination of 
the disturbance caused by the iron on the compass in each ship, — or the deviation of 
the compass as it is now familiarly known to seamen, — was directed to be made by the 
Lords Commissioners of the Admiralty ; the records of this examination are duly pre- 
served in the Hydrographic Office, and have been employed in this investigation. 
The compass specially selected at this period (and since retained with a few modifi- 
cations) for the navigation of Her Majesty’s ships, and with which all observations for 
the deviation are made, and to which the steering or binnacle compasses of the ship 
are referred, is well known as the “Admiralty Standard*.” This compass is solidly 
fixed in the middle line of the ship, within the limits of the quarter-deck ; generally at 
a distance from the stern varying from one-fifth to one-tenth of the vessel’s length, and 
raised sufficiently high from the deck to secure bearings of terrestrial objects above the 
gunwales or bulwarks, which ensures a height varying from about 4 feet 6 inches to 
6 feet 6 inches ; an essential condition of its arrangement being that it is kept as free 
from the immediate vicinity of iron as the nature and equipment of the vessel will 
permit. 
The details of all the essential parts of the Admiralty Standard compass, including 
* A brief description of tbis compass, and the chief points in its construction, is appended. 
MDCCCLX. 2 Z 
