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XIX. On the Amount and Changes of the Polar Magnetism at certain positions in Her 
Majesty's Iron-built and Armour-plated Ship 4 Northumberland .’ By Frederick 
John Evans, Staff Captain , R.N., F.R.S., Chief Naval Assistant , Hydrographic 
Department, Admiralty. 
Received March 5, — Read March 26, 1868. 
In the year 1860 an official report made by me on the Deviations of the Compass 
observed in all the Iron-built Ships, and in a selection of Wood-built Ships in Her 
Majesty’s Navy, and in the Iron Steam-ship 4 Great Eastern,’ was communicated by 
Captain Washington, E.N., F.R.S., the Hydrographer of the Admiralty, to the Royal 
Society, and was published in the Philosophical Transactions for 1860, p. 3.37. 
In the year 1865, with the sanction of the Lords Commissioners of the Admiralty, and 
in conjunction with Archibald Smith, Esq., F.R S., I presented to the Society a paper 
on the Magnetic Character of the Armour-plated Ships of the Royal Navy, which was 
published in the Philosophical Transactions for 1865, p. 263. 
These papers contained a reduction and discussion of observations of the deviations 
of the compass, and of the horizontal and vertical magnetic force made on board a large 
number of iron-built ships at different positions in the ship, at different times, and in 
different geographical positions ; and comprised almost all the results of any value or 
importance regarding the deviations of the compass which up to the time of that publi- 
cation had been obtained in the classes of ships to which they related. 
The system pursued in the Compass Department of the Royal Navy of making careful 
observations whenever the occasion offers, of the deviations and horizontal and vertical 
force in the ships of the Royal Navy, and of reducing such observations so as to obtain 
the magnetic coefficients 3f, SS, (S, 2), X, (*, will, I hope, enable me hereafter to lay before 
the Society a continuation of the former papers, in which I trust one of the deficiencies, 
viz. the want of a variety of observations made in the same ship in different geographi- 
cal positions, will be removed by the zeal of the Navigating Officers now serving in 
several of Her Majesty’s ships on foreign stations. 
In the meantime I take the opportunity of an unusually detailed set of observations 
having been made in the latest and largest of the armour-plated ships, the 4 Northum- 
berland*,’ to lay before the Society, with the sanction of the Lords Commissioners of the 
* The observations discussed in this paper were made, and the coefficients computed, by Staff Commander 
William: Maxes, my successor as Superintendent of Compasses of Her Majesty’s Navy ; and I am happy to have an 
opportunity of bearing testimony to the care and zeal with which he has discharged the duties of his office. I 
MDOCCLXVII1. 3 Y 
