dependent of the anomalies occasioned by the variations in the action of the Sun and Moon.

From the preceding explanation, it is evident that the greatest and least tides ought to follow the movement of that body which exerts the greatest action on the waters. If the solar tides, for instance, destroy the lunar, the times of high and low water ought to coincide with the time at which the solar tide would take place; but if the lunar effects destroy the solar, then the contrary must happen, and the least compound tide ought to correspond with the low solar tide; and consequently the time is a quarter of a-day from that of the greatest compound tide these data, therefore, furnish a simple method of ascertaining whether the solar or the lunar tide is the greatest. Observations show that the time of low water differs by a quarter of a day from that of high water, from which it follows that the action of the Moon surpasses that of the Sun. Laplace made many observations on the heights of the tides, and the intervals between them, at Brest, which is very favourably situated for this purpose, and found that the greatest total tide during each month was 5.888 metres, and the least 2.789 metres; these heights, therefore, are nearly as 2:1. From which it follows, that the action of the Moon is nearly three times as great as that of the Sun.

The height of the tides, as well as the times at which they happen, ought to vary in consequence both of the irregular motions of the Earth and the Moon in their orbits, and the inclination of the two orbits to each other. For by the movement of the Moon in her elliptic orbit, her distance from the Earth varies, and the same effect is produced with respect to the distance of the Earth from the Sun by its motion in its orbit; and as the action of gravity is in the inverse ratio of the squares of the distances from the attracting bodies, it follows that these irregular movements must cause the heights of the tides which result

from these attractions to vary also. If the orbits were in the same plane, the action of these two bodies would also be in the same plane; but the further their orbits deviate from this common plane, or the greater angle they make with each other, the more their forces will be opposed, and consequently the less will be their combined effect.

The time of high and low water depends upon the distance of the Sun from the resultant of the actions of the two bodies; this distance, which is nothing in the syzygies and quadratures, varies in all other positions in proportion to the angle formed by the radii vectores of the two bodies; and this angle varies with the distance of the Moon from the nodes of her orbit. From this, it results that the times of high and low water ought to vary with the inclination of the orbits, and also with the distance of the Moon from her nodes. As all these motions result from the action of gravity, it follows that this force is the efficient cause which produces the tides.

Since, then, both the height of the tides and the time of their recurrence vary according to the movements of the Earth and Moon in their respective orbits, and the inclination of these orbits to each other, and these are subject to periodic revolutions, it necessarily follows that the tides must also be subject to the same periodic variations. The period of these positions of the Sun and Moon with respect to the Earth, is about 223 lunar months, and therefore that of the tides must follow the same period: and as the revolution of the Earth with respect to the lunar nodes is 346-61995 days, during this interval there ought to be two very high and two very low tides. In the comparison which Laplace made of his results, calculated according to these principles, and the phenomena of the tides as actually observed at Brest, the results were found to agree with great precision.

In this explanation of the phenomena of the tides, it has been supposed that the sea covered the whole

globe, and that its depth was every where the same; and though this supposition greatly simplifies the consideration, it is not really the case; for not only is its surface greatly diversified with land, but its depth also presents the greatest variations; and both these modify the general conclusion which have been derived from the preceding theory. These, combined with local circumstances, often cause the tides at any given place not only to differ greatly from that which ought to result from the general theory, but also from the same phenomena, at places not very distant from it. The action of the Sun and Moon upon any space covered with water is the greater in proportion to the extent and depth of the fluid; for the impressions which each molecule of the fluid receives is communicated to the whole mass; and on this account the action of the Sun and Moon, which are insensible upon an insulated molecule, produce such remarkable effects on the whole ocean. Hence we perceive the reason why the flux and reflux are so small in narrow seas; as the Black sea, the Caspian, the Mediterranean, and the Baltic. The direction of the coasts, likewise, has a great influence upon the height and time of the flux in local situations; for when these oppose the general action of the waters, and confine them within certain limits, these waters must accumulate there, and both the height and duration of the tide be increased. The shape of the seas, the directions of their coasts, and their communications with each other, as well as their extent and depth, must also affect the height, the time of high water, and the duration of the tides; and when these are duly considered, and their particular effects fully estimated, they will be found sufficient to account for these anomalies in the phenomena, which constant observation establishes, and which therefore confirm the general theory and effects of gravitation rather than oppose them.

[To be continued.]

The Naturalist's Diary

For NOVEMBER 1819.

Dark is the morn, and thro' the air
The spirit of the tempests flies:
Nature, of late so bright and fair,
Adorned with flowers of thousand dyes,
All beauteous to the view,

Now, shrinking from the tyrant blast,
Appears a desolated waste,

And reads this lesson to the mind,--

Such is the fate of human kind,
So sorrowful, yet true.

The voice of melody, that late
Re-echoed to the listening grove,
Has it, alas! so short a date-
Is all on which we fix our love
So perishing and frail ?
'Tis but as yesterday, the scene
In varied robes of cheerful green,
From early morn to closing day,
Looked rich, and beautiful, and gay,
And told a lovelier tale.

NOVEMBER Comes-and at his call
The genius of the storm awakes:
Flow'rs fade, and leaves deciduous fall-
The vision flies-the enchantment breaks,
And vanishes away.

Now, drenched with cold and cheerless rains,
The Shepherd 'tends his fleecy, care,
And wetshod traverses the plains,
Awhile with summer-beauty fair:
In his sad eye and aching breast,
In all this moral stands confest,

That Life's a Summer's day.

NOVEMBER is, usually, a very gloomy month, yet there are some intervals of clear and pleasant weather: the mornings are, occasionally, sharp, but the hoarfrost is soon dissipated by the Sun, and a fine open day follows. The trees are now stripped of their foliage. See our last volume, p. 294. On the decay and fall of the leaf, see also T. T. for 1817, p. 333, and in the Naturalist's Diary, for October and

1

November, in our former volumes. A popular description of Forest Trees, alphabetically arranged, at the close of the different months, will be found in T. T. for 1816.

The Virginia-creeper (hedera quinque-folia) is particularly rich and beautiful in the autumnal months, with its leaves of every hue, from a bright to a dark green and deep crimson.

That highly-esteemed fish, the salmon, now ascends rivers to deposit its spawn in their gravelly beds, at a great distance from their mouths; thus described by an old poet:

As when the SALMON seeks a fresher stream to find;
Which hither from the sea comes, yearly, by his kind,
As he tow'rds season grows; and stems the watery tract,
Where Tivy, falling down, makes a high cataract,
Forced by the rising rocks that there her course oppose,
As tho' within her bounds they meant her to inclose:-
Here, when the labouring fish does at the foot arrive,
And finds that by his strength he does but vainly strive;
His tail takes in his mouth, and, bending like a bow
That's to full compass drawn, aloft himself doth throw;
Then springing at his height, as doth a little wand,

That bended end to end, and started from man's hand.

In this month, in the year 1817, which was a wet season and very mild, the garden was still gay with holyoaks, marigolds, periwinkle, wallflower, carnation, rose-campion, double daisy, purple primrose, scorpio senna, St. John's wort, mignionette, Michaelmas daisy, golden rod, honeysuckle, rocket, veronica spicata, sweet pea, bog ranunculus, polyanthus, crysanthemums, hepaticas, and mezereon berries. The sallow also disclosed its grey hairy catkins, the hazel its male catkins, and the honeysuckles put out fresh leaf-buds. In the fields, the thistle and the knobweed displayed their rich purple flowers; the yellow of the charlock looked gay amid the green of the turnips, or upon the fallows; and the bramble showed its flowers along with its black berries in the hedges.

What were in summer the fallows grey' are now green with young rye and wheat. If the autumn and