If we suppose an electrified body F attracting an unelectrified body A B D E, the latter moves towards the former.

As we have already seen, the effect of the attraction of F upon A B D E is to increase the tendency of the particles in the hemisphere A E B to move towards it, and to diminish the tendency of those in A D B to move away from it, the resultant tendency is to move towards it.

For to give a further illustration (Fig. 7), if we suppose

acting on C, it will remain at rest; but if we make the force D C less by F C, and E C greater by F G, it is plain that C will move to G, the resultant being the sum of the two additional forces. In other words, if we subtract a quantity from one side of an equation, and add a quantity to the other side, the result would be the same if we added the sum of the quantities to one side, or subtracted their sum from the other.

In Fig. 6, according to the language employed by electricians, the body A B D E is negatively electrified on the side next F, and positively on the further side. Employing the same terms, we may say that the sun is an electrified body producing negative electricity on that side of the globe next it, and positive on the further side, the result being to cause the earth to move towards it.

The attractions and repulsions of electricity and magnetism may thus be considered only special cases of the simple law of attraction.

In consideration of the great importance and far-reaching character of this principle, which I think can hardly be over-estimated, I may be pardoned if in a word or two I attempt to indicate a number of phenomena on which it throws a flood of light.

The currents and tides of the ocean are explicable from the same cause the water under the sun being specifically lighter, a depression, if we may so call it, followed by an elevation, produces the circulation which a glance at a physical chart of the globe will show to be similar to that already pointed out as obtaining in the atmosphere.

Earthquakes are also referable to the depression caused by the

sun, and to the effort made by the strata north and south to restore the equilibrium.

The geological distribution of the strata may be attributed to the same cause, also the absence of any atmosphere on the side of the moon next the earth and the abundant traces of volcanic action observable on its surface.

Sun spots may probably be cyclones secondary to depressions formed by the planets in the sun's equatorial regions.

Indeed the immense number of natural phenomena which it seems satisfactorily to explain is a fourth proof, if any were needed, of its truth.

I have not considered the moon's attraction, but it is obvious that the reasoning equally applies to it. The table of currents is mainly based upon the movements of the moon.

We have now seen that all the motions of the atmosphere are mainly caused by two depressions, one formed by the sun and the other by the moon, and as the sun is more persistent in its action than the moon, I believe the general circulation is mainly due to it and the local differences to the moon, for the latter goes through all the changes in each month of 271 days which the former only undergoes once a year.

Starting from the fundamental principles of the gradient and the deviation of the wind, we have learned

1st. That the great gradients are formed by a depression due to the attractive force of the sun.

2nd. That these gradients have a rotatory motion owing to the movement of that depression westwards.

3rd. That they have a progressive motion north and south following the varying declination of the sun; and,

4th. That they have an oscillating movement advancing towards the depression and receding from the following compression.

The depression formed by the moon will also produce similar gradients, with rotatory, progressive and oscillating movements.

Perhaps I should not conclude this paper without noticing briefly the explanation usually given of the deviation of the trade winds. This is ascribed to the varying rotational velocity of different places on the earth's surface: for example, while bodies on the equator

are whirled round at the rate of about one thousand miles an hour, those north and south are carried round at a slower rate-the speed gradually diminishing towards the poles. A north wind setting towards the equator is therefore continually passing over places which have a higher rotational velocity than the region in which it originated, and it is thus supposed to lag behind and, gradually deviating to the right, become the north-east trade wind. One or two considerations will, I imagine, suffice to show that this position is untenable. The difference between the rotational velocity at the equator and that at 20° N. lat. may be stated roughly at 50 miles per hour, and the average deviation within the tropics at 21 miles per degree or 65 yards a mile per hour. Is it conceivable that this will have any appreciable effect in producing the deviation of the trade wind? Besides the atmosphere partaking of the increasing velocity of the earth's surface will naturally act upon the wind and communicate that velocity to it. This action of the surrounding atmosphere upon the current of air is too often overlooked in making the explanation. Like a well-constructed ship, which responds with unerring precision to the slightest motion of the helm, the wind obeys every impulse which it receives.

D. D.

THE TERMS "PORT" AND "STARBOARD.”

R. VYVYAN, of the Emigration Office at Liverpool, has, in a small pamphlet recently published,* drawn attention to the use of the terms "port" and "star

M

board," as applied to the helm, with a view to their abolition amongst seafaring men, and the substitution of the terms "right" and "left" in their stead. As several circumstances have combined to bring such an idea into prominence, and as Mr. Vyvyan is well qualified to form and express opinions on the subject, we propose to devote a few pages to an examination of the whole question, which, if we are not mistaken, involves very grave issues, and deserves very careful handling.

* See Nautical Magazine, 1878 (Vol. 47), page 938.

PORT AND

That there is amongst us a strong feeling that in cases of collision, and of other accidents in narrow waters, wrong helm is often to blame, cannot be denied. It is certain also that a large number of seamen believe that this wrong helm is often given in consequence of the misinterpretation of the order by the helmsmen, and sometimes from the mistaken expressions of the person in command. The belief has found authoritative expression through the Committee which recently sat at the Board of Trade to revise the steering and sailing rules. The Committee propose to strike out the words "shall port her helm," and to insert instead the words "shall alter her course to starboard," in what is the present Article 13. Again, in the clause adopting a system of sound helm signals for steamers, they propose to substitute the words, "I am directing my course to starboard" (or, to port), for the words "I am about to port (or to starboard) my helm." In making these important changes they remark, "the words 'port helm' are omitted in this and subsequent articles. However well understood by English sailors, they are derived from the movements of a tiller, and are not applicable to the modes of steering now in use. Nor are they used by other nations."

Those who, like Mr. Vyvyan, object to the orders to "port" or to "starboard" as now given on board ships, will no doubt claim this action of the Committee as a help to their side of the argument. But we think that there is some difference between the two things. The Committee, in saying that the term "port helm is not used by other nations, probably mean that it is not used in their rendering of the steering and sailing rules; because it would hardly be correct to speak thus of the general use of the terms port and starboard as applied to the helm. To go no further than France we have the familiar expressions "mettre la barre à bábord" or “à tribord," and in other languages there are similar expressions. We can readily see, on a little reflection, that it does not follow because we can expunge the words "port," or "starboard, helm " from the steering and sailing rules that we are, therefore, on the high road to abolish the orders "port the helm," or "starboard the helm." To give an illustration, it may be mentioned that in H.M. Navy, the terms "port helm" and "starboard helm " have

been eliminated from all the signals ordering tactical movements, and the words "turn to starboard" or "turn to port" have been for the last ten years used instead. But yet the orders "port" and “starboard” as applied to the helm, remain just as before. The officer in command now receives a signal to “turn to starboard," but he gives the order "port the helm" by word of mouth. The reason is obvious: the signal speaks of the movement of the ship, while the verbal order speaks of the process, and the instrument, by which that movement is effected.

So that we may expunge all reference to the helm or rudder in every case where we refer to the movement of the ship, without being one whit nearer a change in the orders used afloat. We must have for our use two sets of expressions; one relating to the helm, or rudder, and the other relating to its effect on the ship. The necessity is absolute, because the ship sometimes fails to obey, and sometimes disobeys, the motion of her helm, and we must have language suitable for expressing these differences.

There is a good deal more of the subtle, and the abstruse, about this question, than we are commonly aware of. "port" and "starboard" represent alternative and opposite ideas, and belong to a class of terms which carry opportunities of error about with them, which are inseparable from the ideas, and which no change in the terms will destroy. To the same class belong the terms, "left" and "right," in relation to the banks of a river. "Lefthanded” and “right-handed," as applied to a twist, and other terms of like nature. Few persons, unfamiliar with the use of the terms "right" and "left" banks of a river, can get the ideas the terms are intended to convey without an effort of imagination. You must imagine yourself standing with your back to the source before the terms have any meaning whatever to you. So with a twist: if we look into the bore of a rifled gun, and are told that the rifling has " a right-handed or a left-handed twist" the expression will be meaningless to us, unless we comprehend that we must think only of the upper part of the bore, and close our minds to the lower part altogether. If we do otherwise, there is no meaning for us in the words we hear; for the grooving passes in the upper part of the bore, in exactly the opposite direction to what it does