f 
616 STAFF COMMANDER E. W. CREAK ON THE DEVIATIONS OF THE 
deviation with the ship upright and heeled over. Unfortunately there is a great want 
of observations under these circumstances.” 
During the last fifteen years long voyages into high southern magnetic inclination 
or dip, have been made in every class of ship in the Royal Navy, except Turret- 
ships, and according to the established system of the Admiralty Compass Department, 
the observed deviations of their compasses made in all latitudes have been analysed 
to obtain the values of their coefficients as shown in Table III. of this paper. From 
these coefficients, the constants of the hard and soft iron producing semicircular 
deviation at the Standard Compass positions have been computed. 
A knowledge of these Constants not only provides a means of predicting for the 
particular ship examined the probable changes which will take place in her deviation 
in all parts of the navigable world, but also the power of doing the same for other 
ships of the same class. 
Such being the case, it is thought that the Royal Society will be interested in 
receiving a paper treating of these subjects, commencing from the time the ships are 
fully equipped and ready for sea. The earlier magnetic history of the ships might 
have been included, but the changes which take place in their fitting, and the 
numerous iron bodies introduced after launching, render a comparison of the devia¬ 
tions observed at different stages of equipment unsatisfactory. 
It is proposed to consider six classes of ships, each of which has been, selected for 
the long range of magnetic latitude over which the ships have sailed :— 
1. Iron, armour-plated. 
2. Iron cased with wood. 
3. Iron troop-ships. 
4. Steel'" and iron cased with wood. 
5. Composite built. 
6. Wooden ships with iron beams and vertical bulkheads. 
These ships have nearly all been launched upwards of a year previous to the 
observations about to be discussed, and subjected to the vibration caused by steaming 
at high rates of speed with powerful engines. They may therefore be considered to 
have attained a state of magnetic stability.t 
At the close of this paper will be found in Table III. a short description of the 
ships, the direction in which they were built, and the coefficients for each Standard 
Compass. 
It is not intended to repeat the several mathematical formulae by means of which 
* The vessels have iron frames, and are plated with mild steel, containing 2 per cent, of carbon, 
t See Phil, "frans., 1865, Part I., pp. 279-280. 
