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board in a squall on the 25th, in lat. 40° N., long. 63° W. (the vessel heaving a list to port at the time), sufficed to steam 1,353 miles.

Passed the Bishop lighthouse at 6 p.m. of the 13th of September; and anchored at Falmouth at 7 a.m. of the 14th. Time of passage, 22 days 14 hours from the Delaware lightship. Distance covered, 3,316 miles; steamed, 3,126 miles; and sailed, 190 miles. The weather, though very coarse at times, was generally moderate on the passage, with occasionally a heavy

cross sea.

Between Scilly and Falmouth it was severe in the extreme; hard gale from the S.W. with squalls, rain, and heavy sea. Full steam and all the canvas she could bear barely sufficed to keep her a-head of the sea. Coal left on arrival at Falmouth was sufficient for about six hours' steaming.

Took in ten tons of coal and left on the morning of the 17th September, for London, calling at Ryde, Isle of Wight. Arrived at Erith about 2 p.m. of the 20th; the counter on the engine showing 8,484,245 revolutions.

The general opinion of the American visitors was that of surprise with decided admiration of the engines and boiler, though the steam pressure shown on the gauge, viz., 540 lbs., the highest worked on the trip, often caused them to make a rush on deck out of the engine-room. The boiler, however, being tested to 2,500 lbs. pressure per square inch, is perfectly safe.

The vessel had a small two-bladed fish-tail propeller, consequently her speed was considerably less than it would have been with a three or four-bladed one.

There was no doubt in the minds of practical men who saw them at work that the Perkins' engine and boiler are the best things of the kind now out.

Our American cousins were keenly alive, not only to the economy of fuel and space as demonstrated, but also to the advantages for naval purposes. Gunboats, with these engines and boilers, could blockade a port for a long period without re-coaling.

As a practical seaman, with experience in large and small

steamers, I should prefer the Perkins' engine and boiler to any other, having seen them tested under very trying circumstances. For marine purposes, a slight raising of the boiler would be advantageous.

October 6, 1880.

E. G. DENT.

ON COMPASSES, AND THEIR ADJUSTMENT IN

IRON SHIPS.

(Continued from page 810.)

N the formula p. 740 the effect of coefficient E in the several quadrants is as follows:

Coefficient + E gives or easterly deviation in the North and South quadrants, and or westerly deviation in the East and West quadrants. (Fig. 20.)

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Coefficient E is the reverse of the foregoing, giving - or westerly deviation in the North and South quadrants, and + or easterly deviation in the East and West quadrants. (Fig. 21.)

It may be well to review the totality of the effects of the hori zontal soft iron variously distributed around and below or above the compass-now athwartship and undivided, as in the beams, or divided as for a skylight-or now fore and aft, perhaps divided at the position of one compass, and undivided at that of another.

Soft iron, athwartship, like the beams (Fig. 22), passing as it were through the position of the compass, has the effect of decreasing the mean directive force of the needle, and producing a positive quadrantal deviation.

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But if the 'thwartship iron be divided, as for a skylight (Fig. 23), the effect is an increase of the mean directive force, but a negative quadrantal deviation.

Soft iron extending fore and aft (Fig. 24), and passing through the position of the compass, decreases the directive force, and produces a negative quadrantal deviation.

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But if the fore and aft iron be divided at the position of the compass (Fig. 25), the result is an increase of the directive force, and the production of a positive quadrantal deviation.

In an iron ship, however, it may be taken that the distribution of the horizontal soft iron will generally partake of a combination of the arrangements already indicated.

Thus, if the soft iron be disposed in the position of Figs. 26 and 27, the directive force would be unaltered, if the effect of the fore and aft iron was such as to neutralise that of the athwartship; or it might be increased or diminished according to the excess of

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one over the other. But 26 would give a large positive quadrantal deviation; and 27 a large negative quadrantal deviation; as, however, the latter seldom or never occurs, it is to be presumed that the arrangement of iron that gives it is not found in the usual position of any of the compasses.

The arrangement of soft iron shown in Fig. 28 gives an increase of directive force, with an amount of quadrantal deviation

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depending on the excess of the positive over the negative; it would generally be very small. The same remark, as regards the deviation equally applies to the arrangement of the soft iron shown in Fig. 29, but in this case there would be a decrease of the directive force. The tendency of the disposition of the soft iron magnetised by horizontal induction in the last two cases is, not only to produce quadrantal deviation, but to indirectly affect the amount of the semicircular deviation. Hence the necessity of having a compass not less than four or five feet above all horizontal iron.

It is as well to observe that the term positive in these latter remarks means + or E. deviation in the N.E. and S.W. quadrants, and or W. deviation in the S.E. and N.W. quadrants; negative means the reverse.

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Though the value of coefficient E is generally so small that it may be disregarded, it is, in exceptional cases, sufficiently large to be an important element in the formula. The coefficient D, almost always positive, attains a high value in some ships, but especially in steamers; it is, however, most remarkable for the detrimental effect which the disturbing force that produces it has on the directive force of the needle. Its amount does not depend upon the size of the vessel or on direction when building, but rather on the position of the compass and its surroundings; and from its origin will be unchanging in all magnetic latitudes.

The coefficient A represents the constant deviation, since it appertains to every point of the compass, with the same sign, + or as the case may be, and with the same value. It is due to a variety of causes; the lubber's line not being exactly in the midship line; bad graduation of a compass; inability to read a compass to minutes of arc; lack of precision in the prism; an index error; an unrecognised difference between the compass on shore and that on board; the correct magnetic bearing of a distant object being only known to the nearest degree, &c. Thus the errors may be partly instrumental, and partly due to observation. They are unlikely to be cumulative, and ought therefore to be small; generally less than 1°. In this sense the A is apparent rather than real, and may have different values at different places and times. It is reckoned + when the easterly deviation is in excess, and when the westerly deviation is in excess.

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But there may be a real constant, A, with a large value, due to horizontal induction in soft iron placed unsymmetrically in respect to the position of two compasses out of the midship line; one such compass being to starboard and the other to port of the elongated end of the iron spindle of the steering wheel. (See Fig. 80.) The result will be + A in the starboard compass, and - A in the port compass, since the south ends of the needles must be attracted towards the end of the spindle when the ship heads in any northerly direction, and the north ends of the needle will be similarly attracted when the ship heads in any southerly direction; and this will occur irrespective of change of magnetic latitude. The co-efficient E will also be appreciably affected from the same cause, since A and E are closely connected.

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FIG. 30.

A Deviation Curve. It is not my intention to explain the use of Napier's diagram, which is undoubtedly the best and most simple graphic solution of the deviation problem that has yet appeared, and is on that account not likely to be soon superseded: it requires no calculation-merely the result of observations made on eight nearly equi-distant points-and a moderate degree of neat-handed

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