[Heave the vast spars. l. 116. Water in descending down elevated situations if the outlet for it below is not sufficient for its emission acts with a force equal to the height of the column, as is seen in an experimental machine called the philosophical bellows, in which a few pints of water are made to raise many hundred pounds. To this cause is to be ascribed many large promontories of ice being occasionally thrown down from the glaciers; rocks have likewise been thrown from the sides of mountains by the same cause, and large portions of earth have been removed many hundred yards from their situations at the foot of mountains. On inspecting the locomotion of about thirty acres of earth with a small house near Bilder's Bridge in Shropshire, about twenty years ago, from the foot of a mountain towards the river, I well remember it bore all the marks of having been thus lifted up, pushed away, and as it were crumpled into ridges, by a column of water contained in the mountain.
From water being thus confined in high columns between the strata of mountainous countries it has often happened that when wells or perforations have been made into the earth, that springs have arisen much above the surface of the new well. When the new bridge was building at Dublin Mr. G. Semple found a spring in the bed of the river where he meant to lay the foundation of a pierre, which, by fixing iron pipes into it, he raised many feet. Treatise on Building in Water, by G. Semple. From having observed a valley north-west of St. Alkmond's well near Derby, at the head of which that spring of water once probably existed, and by its current formed the valley, (but which in after times found its way out in its present situation,) I suspect that St. Alkmond's well might by building round it be raised high enough to supply many streets in Derby with spring-water which are now only supplied with river-water. See an account of an artificial spring of water, Phil. Trans. Vol. LXXV. p. 1.
In making a well at Sheerness the water rose 300 feet above its source in the well. Phil. Trans. Vol. LXXIV. And at Hartford in Connecticut there is a well which was dug seventy feet deep before water was found, then in boring an augur-hole through a rock the water rose so fast as to make it difficult to keep it dry by pumps till they could blow the hole larger by gunpowder, which was no sooner accomplished than it filled and run over, and has been a brook for near a century. Travels through America. Lond. 1789. Lane.]
IV. "Sailing in air, when dark MONSOON inshrouds
130 His tropic mountains in a night of clouds;
Or drawn by whirlwinds from the Line returns,
And showers o'er Afric all his thousand urns;
High o'er his head the beams of SIRIUS glow,
And, Dog of Nile, ANUBIS barks below.
135 NYMPHS! YOU from cliff to cliff attendant guide
In headlong cataracts the impetuous tide;
Or lead o'er wastes of Abyssinian sands
The bright expanse to EGYPT'S shower-less lands.
—Her long canals the sacred waters fill,
140 And edge with silver every peopled hill;
Gigantic SPHINX in circling waves admire;
And MEMNON bending o'er his broken lyre;
O'er furrow'd glebes and green savannas sweep,
And towns and temples laugh amid the deep.
[Dark monsoon inshrouds. l. 129. When from any peculiar situations of land in respect to sea the tropic becomes more heated, when the sun is vertical over it, than the line, the periodical winds called monsoons are produced, and these are attended by rainy seasons; for as the air at the tropic is now more heated than at the line it ascends by decrease of its specific gravity, and floods of air rush in both from the South West and North East, and these being one warmer than the other the rain is precipitated by their mixture as observed by Dr. Hutton. See additional notes, No. XXV. All late travellers have ascribed the rise of the Nile to the monsoons which deluge Nubia and Abyssinia with rain. The whirling of the ascending air was even seen by Mr. Bruce in Abyssinia; he says, "every morning a small cloud began to whirl round, and presently after the whole heavens became covered with clouds," by this vortex of ascending air the N.E. winds and the S.W. winds, which flow in to supply the place of the ascending column, became mixed more rapidly and deposited their rain in greater abundance.
Mr. Volney observes that the time of the rising of the Nile commences about the 19th of June, and that Abyssinia and the adjacent parts of Africa are deluged with rain in May, June, and July, and produce a mass of water which is three months in draining off. The Abbe Le Pluche observes that as Sirius, or the dog-star, rose at the time of the commencement of the flood its rising was watched by the astronomers, and notice given of the approach of inundation by hanging the figure of Anubis, which was that of a man with a dog's head, upon all their temples. Histoire de Ciel.]
[Illustration: Fertilization of Egypt.]
[Egypt's shower-less lands. l. 138. There seem to be two situations which may be conceived to be exempted from rain falling upon them, one where the constant trade-winds meet beneath the line, for here two regions of warm air are mixed together, and thence do not seem to have any cause to precipitate their vapour; and the other is, where the winds are brought from colder climates and become warmer by their contact with the earth of a warmer one. Thus Lower Egypt is a flat country warmed by the sun more than the higher lands of one side of it, and than the Mediterranean on the other; and hence the winds which blow over it acquire greater warmth, which ever way they come, than they possessed before, and in consequence have a tendency to acquire and not to part with their vapour like the north-east winds of this country. There is said to be a narrow spot upon the coast of Peru where rain seldom occurs, at the same time according to Ulloa on the mountainous regions of the Andes beyond there is almost perpetual rain. For the wind blows uniformly upon this hot part of the coast of Peru, but no cause of devaporation occurs till it begins to ascend the mountainous Andes, and then its own expansion produces cold sufficient to condense its vapour.]
145 V. 1. "High in the frozen North where HECCLA glows,
And melts in torrents his coeval snows;
O'er isles and oceans sheds a sanguine light,
Or shoots red stars amid the ebon night;
When, at his base intomb'd, with bellowing sound
150 Fell GIESAR roar'd, and struggling shook the ground;
Pour'd from red nostrils, with her scalding breath,
A boiling deluge o'er the blasted heath;
And, wide in air, in misty volumes hurl'd
Contagious atoms o'er the alarmed world;
155 NYMPHS! YOUR bold myriads broke the infernal spell,
And crush'd the Sorceress in her flinty cell.
[Fell Giesar roar'd. l. 150. The boiling column of water at Giesar in Iceland was nineteen feet in diameter, and sometimes rose to the height of ninety-two feet. On cooling it deposited a siliceous matter or chalcedony forming a bason round its base. The heat of this water before it rose out of the earth could not be ascertained, as water looses all its heat above 212 (as soon as it is at liberty to expand) by the exhalation of a part, but the flinty bason which is deposited from it shews that water with great degrees of heat will dissolve siliceous matter. Van Troil's Letters on Iceland. Since the above account in the year 1780 this part of Iceland has been destroyed by an earthquake or covered with lava, which was probably effected by the force of aqueous steam, a greater quantity of water falling on the subterraneous fires than could escape by the antient outlets and generating an increased quantity of vapour. For the dispersion of contagious vapours from volcanos see an account of the Harmattan in the notes on Chunda, Vol. II.]