IN THE lEON SHIPS OF THE EOTAL NAVY. 
349 
The Torch is a special example. This vessel was sold out of Her Majesty’s service 
at Sydney, after a continuous service of three years in Australia (1853 to 1856) in high 
south magnetic latitudes; in July 1856 she was chartered by the Colonial government 
of New South Wales to proceed to the northern coast of Australia to render assistance 
to an exploring expedition. The officer who had previously been in command, Lieut. 
Wm. Chimmo, R.N., was the Government agent on this occasion, and on the passage, 
especially along the eastern shores of Australia, that officer made numerous observations 
for the Variation of the Compass (the direction of the ship’s head being noted to each), 
which were transmitted to the Admiralty. From these observations, compared with 
the well-known variation in these seas, I was enabled graphically to construct a curve 
of deviation : the results 'are given, and are confirmatory of the general permanent 
nature of the ship’s magnetism under circumstances which 1 apprehend are novel, and 
not without value in a theoretical discussion. 
The conclusions derived from a review of the foregoing results are not unimportant ; 
and not the least of these in practical value, is that in an iron ship of ordinary dimen- 
sions, and of conditions similar to the examples quoted, a standard compass can be 
placed, the deviations of which will but little exceed those obtaining in wood-built 
steam-ships ; and further, that on a change of geographic position, however great, these 
compass deviations will be within smaller limits, and can be approximately predicted. 
A divergence from these conditions will arise when the inductive magnetism of the 
hull or machinery predominates. If we may judge from the case of the Royal 
Charter, whose magnetic elements have been so ably discussed by various authorities, 
large quadrantal deviation and fluctuating sub-permanent magnetism (due to hull 
alone) are coexistent, and give rise to conditions of compass-disturbance which are 
beyond prediction, have hitherto baffled inquiry, and given a complexion to theoretical 
deductions varying as regarded from different points of view. 
Ohser tions on the early changes of an Iron-huilt ship’s Magnetism, illustrated hy expe- 
riments in the Steam-Ship Great Eastern. 
The opinion has been long entertained, that the original magnetism of an iron-built 
ship, or that acquhed in the process of building, undergoes a rapid change after 
launching, and that from this cause accidents have occurred to recently launched and 
hastily equipped vessels. The records of ships of the Royal Navy do not illustrate this 
subject. 
The unusual dimensions of the Great Eastern, and the interest attaching to the pro- 
gress and success of so great an undertaking, pointed her out as a desirable ship to test 
in elucidation of various problems connected with the mariner’s compass, and especially 
of the supposed early changes in the ship’s magnetic force. 
Through the kindness of the Directors, and partly in the nature of assistance sought 
for by that body from the Lords of the Admiralty, I was enabled to make many 
