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earlier boats in the French Navy were designed to be armed with spar torpedoes; those of the last type built in France are to carry the Whitehead, and are of 33 tons displacement, and 92 feet long, with a speed of 19 to 20 knots. The plates are of steel, and are said to be three to five millimetres (roughly two to threesixteenths of an inch) thick.

Our own Government has been blamed for not having gone in for torpedo boats more extensively and at an earlier date. They were certainly rather behind hand in adopting the new engine of naval warfare, but we think that possibly they were, and are right in exercising some caution as to the amount of money to be spent upon vessels which may be superseded in a few years by others, perhaps faster and more efficient. The mere fact that Russia in so short a time got together so large a number as a hundred would indicate that this branch of the Navy is one in which we may to some extent trust to our great facilities for rapid increase when the boats are likely to be required. In this regard it is worthy of note that the large majority of torpedo vessels, of all sizes, have been built in England.

Large ironclads take years to build, and no amount of money can in an emergency make up for lost time, as far as they are concerned, but, as regards the small torpedo craft, it would appear to be the wisest course to increase their numbers gradually, thus acquiring experience as to the respective capabilities of various classes of boats. It must also be remembered that these vessels are of necessity comparatively short-lived. They trust to their high speed for safety in presence of a heavily-armed enemy, who has difficulty in hitting a rapidly moving object, and high speed is obtained by cutting down the weight carried to a minimum-hence the plating is of necessity so thin that a very small amount of deterioration tells heavily upon it.

It is difficult, in the present state of our knowledge, to estimate the relative importance of the torpedo boat in naval wars of the future. In the defence of harbours it, in combination with submarine mines, will doubtless be largely used, but in a great battle on the high seas our present experience would appear to indicate that the big gun and the ram will both be more important weapons than the torpedo.

ON COMPASSES, AND THEIR ADJUSTMENT IN
IRON SHIPS.

(Concluded from page 903.)

HE HEELING ERROR. All that has been said so

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far relates to a ship when upright, that is, to a ship on an even beam and keel, which should be her position when swung for the deviation of the compass, or for the adjustment of any of them; and be it remembered that though the compasses have been adjusted in respect to the semicircular and quadrantal co-efficients, the effect of the correction is not such as to efface, though it may mitigate, the heeling deviation.

The following diagrams, 32 and 33, in respect to a ship built head towards North in the northern hemisphere, illustrate the effect of the magnetism as she heels over; and the worst possible position for a compass in such a ship is near the stern, for there all the forces conspire to magnify the error.

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It is easily seen that, as the ship heels over, the transverse iron, such as the deck beams, becomes magnetic as it inclines, and the upper or weather end, s, (with blue magnetism) attracts the N. (red) point of the needle; further, the upper end of the soft iron, which, before heeling, acted vertically below the compass and did not disturb the horizontal needle, is now with its s, or blue magnetism, brought out to windward, and is consequently an additional force pulling the N. point of the needle to windward; to this must be added the effect of the vertical force of the subpermanent magnetism, which, according to circumstances, may act

upwards or downwards. The heeling deviation is, in this case, to the high or weather side, whether heeling to starboard or port.

Since, however, the effect of induction will be changed at the magnetic equator, and will be reversed, as the upper end of the iron acquires magnetism south of the equator, the heeling error, to state a general case, arises from the following causes:

1. Vertical induction in transverse iron, which draws the N. end of the needle to windward in N. latitudes, and to leeward in S. latitudes.

2. Vertical force arising from sub-permanent magnetism; and vertical induction in vertical iron; which, in the usual position of the steering (aft) compass, draws the N. end of the needle to windward in ships built head North, to leeward in ships built head South.

Hence, an iron ship, built head North, will generally have a large heeling error to windward in N. latitude; and a small heeling error, which may be to windward or to leeward, in S. latitude.

Also, an iron ship, built head South, may be expected to have a small heeling error to windward or to leeward in N. latitude, and a considerable heeling error to leeward in S. latitude.

The heeling error being a maximum on the North and South points by compass, and nil at East and West, it is evident that the coefficient C is that which must be most affected, and if the deviation for an upright ship be,

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we shall have, for a ship heeling n degrees, with c taken to be the change in C for one degree of heel, the following formula

or,

dn

dn

= B sin z + (C + c no) cos z + D sin 2 z

= d+cno cos z

that is, the heeling error alters proportionally to the number of degrees of heel and the cosine of the azimuth of the ship's head.

It is possible to put this, for practical purposes, in a more simple form. Since, in the northern hemisphere, in the majority of iron ships, the North end of the compass needle is drawn to windward (to the weather, or high, side) when the binnacles are above

the upper deck, the following results, as neatly put by Captain Evans, R.N., would arise from a disregard of this heeling error:

"If the ship be kept steady on one compass course, she will be found to windward of her supposed position when on northerly courses; and to leeward on southerly courses. If she be steered steadily for a fixed point on the horizon, she will appear to fall off as she heels on northerly courses, and to come up on southerly courses." Therefore, as a general rule, it should be borne in mind "that in steering by compass and wishing to make a straight course, we must keep away, by compass, on either tack, as the ship heels, when on northerly courses; and keep closer to the wind, by compass, on either tack, when on southerly courses."

Every seaman will apprehend this plain language; but to express the heeling deviation in terms of the deviation when upright, the following are the results:

ON NORTHERLY COURSES,

Starboard tack, E. dev. is increased, W. dev. is decreased.
Port tack,-W. dev. is increased, E. dev. is decreased.

ON SOUTHERLY COURSES,

Starboard tack,-W. dev. is increased, E. dev. is decreased. Port tack, E. dev. is increased, W. dev. is decreased. And it can easily be understood that when the upright deviation is small in amount and decreases from heeling, it may go to the extent of being reversed in name.

Observe further that there is a correspondence between the starboard tack on Northerly courses and the port tack on Southerly courses; also between the port tack on Northerly courses and the starboard tack on Southerly courses.

When the North end of the compass needle is drawn to leeward, the rule above is of course reversed.

As some may better understand the naming of the heeling error if given according to the tack, it can be expressed as follows:1. When N. end of the compass needle is drawn to the weather side

On starboard tack, heeling error is E. on Northerly courses;
W. on Southerly courses.

On port tack, heeling error is W. on Northerly courses;
E. on Southerly courses.

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2. When N. end of the compass needle is drawn to the lee side— On starboard tack, heeling error is W. on Northerly courses; E. on Southerly courses.

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On port tack, heeling error is E. on Northerly courses;

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1. If, on changing tack, the course is changed from Northerly to Southerly, or from Southerly to Northerly, the heeling error does not change its name.

2. If, on changing tack, the course still remains Northerly, or still remains Southerly, the heeling error changes its name; also

3. If, without tacking, by a change of wind the course changes from Northerly to Southerly, or from Southerly to Northerly, the healing error changes its name.

These observations do not apply to the amount of heeling error, which of course, depends on the extent, or number of degrees, of heeling.

The amount of heeling error with the ship's head North or South, on which points it is a maximum, varies greatly in different ships. Something between ° to 2° for every degree of heel is by no means unusual, and it has been found to be as large as 3°; in very rare instances the latter amount may be exceeded, but there is no sufficient proof of this. The amount of heeling error in one ship is no criterion for estimating that in another, though both ships may have been built in the same magnetic direction.

TO ADJUST THE COMPASS, OR CORRECT THE DEVIATION, WITH PERMANENT MAGNETS AND SOFT IRON.-It is taken for granted that the reader understands the use of azimuthal bearings-it may be of a distant object on shore-or reciprocal, as is sometimes compulsory-or of a celestial body, as the sun, a planet, or a fixed star; any of which may, according to circumstances, and the locality, be employed while swinging a ship, and bringing her head to any given number of correct magnetic directions, for the purpose

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