354 
ME. EVAIs'S OJs" THE DEYIATIOX OF THE C03IPASS 
In vessels built head North or South, the conditions arise, that in the fonner the 
attraction is toward the stern (the topsides in their action being neutral to a compass 
in the middle line of the deck), and diminishes in force as the compass is moved 
towards the bow. In the latter the law is reversed, and small compass deAiations are 
obtained as the stern is approached. 
■ In an iron sailing ship, built head to South, there will be an attraction of the north 
point of the compass to the head, and if built head to North, a like attraction to the 
ship’s stern ; and so far there would seem to be no advantage in one du’ection over the 
other. But in the first case the topsides near the compass have weak magnetism ; in 
the second case they are strongly magnetic : the first position seems therefore preferable. 
In an iron steam-ship, built head to the South, the attraction due to machineiy is 
added to that of the hull, whereas in one built head to the North, the attractive forces 
of hull and machinery are, in the northern hemisphere, antagonistic, and a position of 
small, or no “ semicircular ” deviation for the compass may generally be obtained. To 
iron steam-vessels engaged on the home or foreign trades in the northern hemisphere, 
this direction of build is therefore to be preferred. 
2. On the Position and Arrangements for the Comjmss. 
The position of compasses, whether standard or steering, must depend, as -v^-ill have 
been observed from the foregoing conclusions, on the direction of the ship's build ; that 
is, in those built head North the compass must be as far removed from the stern as 
circumstances will permit ; in those built South, placed as near to the stern as convenient, 
without approaching so close to the rudder-head or iron tafifrail as to cause the ship's 
general magnetism to be overpowered by the magnetic influence of those masses. 
In ships built East or West there is little choice of position, except to avoid, as a 
general rule, proximity to vertical masses of iron ; in vessels built uith their heads on 
the intercardinal points, a position approximating to the bow or stern respectively, 
where the action from tlie topsides (to be determined experimentally) is at a minimum, 
is to be preferred. 
Ample elevation above the deck, and to be strictly confined to the middle line of the 
ship, are the primary conditions of position for every compass in an iron ship, and no 
compass, whether steering or standard, should be nearer the iron deck beams than 
4 feet * : for the steering compass this arrangement could be met by the use of a 
vertical card for the helmsman. 
The standard compass, which as a rule I should recommend to be invariably uncom- 
pensated, requires an elevation of at least 5 or 6 feet from the deck, and to be fitted on 
* A curious illustration of the effect of iron deck beams on long and short compass-needles resulted from 
some experiments made on board H.M.S. Bloodhound : on the deck, or within a few inches of the 
position where, not unfrequently, hanging or tell-tale compasses are placed, a 10-inch needle had 43'^, a 
6-inch needle 38°, and a 1^-inch needle 33° diflerence from their uniform deviation at 1 foot 9 inches from 
the deck. 
