issue from the ground close to the edge of the briny ocean; and along the sandy bays in the Scotland district, fresh water may be easily obtained by digging holes in the sand from 10 inches to 3 feet deep; they are almost instantaneously filled with fresh water. At the low Coral Island of Anegada, fresh water is procured in a similar manner, and under still more surprising circumstances, as the sandy beach is frequently bordered on one side by the sea, and on the other by salt ponds1. The water which percolates the calcareous rock is generally of a pleasant taste; wells are therefore sunk, according to the elevation above the level of the sea, to a considerable depth, in order to supply water for domestic purposes. The purest water is found when on digging a stratum of clay and gravel is reached, which generally will be found to be nearly on the same level with the sea. Some of the deepest wells are from 35 to 40 fathoms in depth. A supply of water is likewise preserved in reservoirs, which are in a great measure of natural construction, assisted by art. The surface in the calcareous or coralline part of the island is frequently broken by numerous cavities and basin-like hollows. These depressions are rendered impervious by an artificial structure of layers of clay; and during the rainy season they receive the rain-water from the adjacent fields, and are chiefly used for the cattle; but during severe dry weather, these ponds, as they are called, are likewise resorted to by man. A greenish scum may be seen on the surface of the pond-water when the weather is very dry; Hughes considers this a strong poison, and observes that it proves fatal to the poultry, and even to black cattle. There is no doubt that the scum consists of animalcules: it requires however a stricter investigation to ascertain whether any dangerous quality is to be ascribed to them. He has given in his 'Natural History of Barbados,' a table of the specific weight of the water from several springs and wells in the island, which I consider of sufficient interest to insert here: I have merely slightly changed the arrangement of the original table. Table of the Specific Weight of fifteen cubic inches of the principal springs, wells, &c. in the Island of Barbados. 15 cub. in. from Mr. Robert Osborne's well-water in the parish of St. Peter, weighed ozs. drs. grs. 8 3 12 " from Belly-ache Hole, at the estate of the Rev. Mr. from the springs near the Bay, by percolation through وو from rain-water received from the eaves after long rain 8 3 14 1 See remarks on Anegada in the Journal of the Royal Geographical Society of London, vol. ii. p. 159. from a weak chalybeate water, in the estate of Mr. Richard Richards, in the parish of St. Andrew. 8 3 14 from Pyrmont water 8 3 19 There are several chalybeate waters to be found in the Scotland district, chiefly at Vaughan's, the Spa and Cheltenham. The two latter places have received their name from the fancied resemblance of the water to the celebrated mineral springs of that name in Europe. I have not been able to procure a correct analysis. Hughes alludes to one on a Mr. Perry's estate in the parish of St. Joseph, which on the application of the powder of gall, turned instantly of a deep purple, and, like the Pyrmont water, resumed its first colour after receiving a few drops of the spirit of vitriol. These springs contain chiefly iron, carbonic acid, and fixed alkali in different proportions. The waters at Cheltenham are purgative and alterative; those where the iron is more abundant, are slightly tonic. The "Boiling Spring," as it is called, is considered one of the great natural curiosities of Barbados. Near the side of a water-course in Turner's-hall Wood, in the parish of St. Andrew, is a small spot, perhaps not more than two feet in diameter. From this space carburetted hydrogen escapes through the soil; an inflammable gas, which on the application of a flame, burns with a pure whitish light. If the shallow excavation which has been made by human hands for this purpose is filled up with water, the gas emanating through it causes an ebullition on the surface which resembles water in a boiling state. I need not remark that the gas does not communicate any heat to the water; on the application of a most sensitive thermometer by Bunten in Paris, I observed no change in the temperature of the water through which the gas escaped. Petroleum or mineral tar oozes from the mountain sides in the argillaceous districts: it is collected in excavations and much used for domestic and medical purposes. As it is my intention to give a more detailed account of this substance in the geological sketch of the island, I must refer my reader to that portion of my work. 13 CHAPTER IV. INTRODUCTORY REMARKS ON CLIMATE IN GENERAL. THE temperature or climate of a country depends upon its distance from the equator. Local circumstances,-as its height above the level of the sea; whether an island or a portion of an extensive continent; the nature of its surface, whether consisting of flats or of mountainous land, --all these combine to operate materially upon the decrease or increase of heat, and to regulate the temperature of the atmosphere. If the surface of our planet represented the same curve, if it were composed of the same material, and covered throughout with a similar vegetation, isothermal lines or lines of equal annual temperature would run parallel to the equator. It is however well-known that this is not the case; and lines passing through places having the same mean annual temperature are sinuous, and differ frequently from 4° to 5° in latitude. In consequence of the more equal temperature of the waters of the ocean, the climate of islands and of coasts deviates considerably from that of the interior of continents. The British Isles give an instance of this in Europe; and the coast of Guiana, when compared with the interior of those regions, presents an example in America. "We find in New York," says Humboldt, "the summer of Rome and the winter of Copenhagen; at Quebec, the summer of Paris and the winter of Petersburgh; at Pekin in China, where the mean temperature of the year is that of the coasts of Brittany, the scorching heats during summer are greater than at Cairo, and the winters as rigorous as at Upsala1". In the torrid zone, on approaching the equator from 30°, the isothermal lines are more parallel to each other. The mean temperature of the tropical regions is between 79° and 83° Fahrenheit. No difference occurs between the observations which have been made at Senegal, Pondichery or Surinam. Under the equator the oscillations of the thermometer are, like those of the barometer, comparatively trifling; this is however not the case in temperate climates, and especially in the latitude of Paris, where the changes are much more considerable2. Humboldt on Isothermal Lines. In order to give an opportunity for a just comparison, I add the latitudes of these places, which are all in the northern hemisphere. Rome 41° 54′; Paris 48° 50′; Cairo 30° 2′; New York 40° 42′; Quebec 46° 47′; Pekin 39° 54′; Copenhagen 55° 41'; Petersburgh 59° 57'; Upsala 59° 52'. * Humboldt, Mémoire sur les lignes isothermes, p. 54. In Cumana Humboldt never saw the thermometer below 69° Fahr., nor above 91° Fahr., the extremes differ therefore 22° Fahr.; while at Paris the thermometer stood on the 25th of January, 1795, 10°-3 Fahr., and on the 8th of January (?June), 1793, 102°-3 Fahr.; showing The difference in the mean temperature under the tropics, when the sun reaches his maximum altitude, compared with the mean temperature when he reaches the minimum altitude, is very trifling. It has been proved, that on ascending high mountains, or during the ascent in balloons, the temperature gradually decreases. Gay-Lussac ascended on the 16th of September, 1805, in a balloon at Paris, to a height of 22,890 feet. The thermometer stood at the surface of the earth 87°-4 Fahr., and at the greatest height which he reached, he found it had sunk to 14°-9 Fahr., or about 17° below the freezing-point. This decrease, to judge from the results which have been hitherto obtained, does not rest upon geometrical principles; and although certain heights have been assumed, at which on ascending the thermometer would fall a degree, much depends upon peculiar circumstances, as the distance from the equator, the season, whether during day or at night, &c. Humboldt gives the following table for the equatorial zone from 0 to 10°. These results give the following data:-On ascending, the thermometer falls 10° in the first 3100 feet, or about 1° for every 310 feet; in the succeeding 3200 feet of ascent, 524 feet are required to produce a fall of 1° in the thermometrical scale; in the third stage it requires an ascent of 430 feet for each degree; in the fourth stage, only an ascent of 244 feet for each degree; and in the last stage, or between 13,000 and 16,000 feet, it approaches again the height during the first stage, and amounts to 320 feet for each degree. The moisture which exists in the air is chiefly ascribable to evaporation from the water on the surface of the earth. If water be exposed to the air, it suffers gradual diminution till it is entirely evaporated. The degree of evaporation depends upon the state of the atmosphere, but chiefly upon the strength of the wind. The process of developing on the surface of the water exposed to the atmosphere small vesicles which mix with the air, is continuous, although not visible to the eye. It is accelerated by heat and wind. This evaporation or development of vesicular bodies does not restrict itself to the water; it likewise occurs from plants, and even from animals; and indeed with every appearance of a a difference of 113°, which is a variation five times greater than in Cumana (Elémens de Géographie Physique et de Météorologie, par H. Lecoq, p. 432). During thirteen years the thermometer never rose in Vera Crux above 98° Fahr., and it stood only three times above 90°; while in Paris it is by no means unfrequent to see it as high as 97° Fahrenheit. serene and dry atmosphere, delicate investigation would prove the presence of aqueous vapours. It is generally believed that these vapours exist in a heated atmosphere in a larger quantity than when at a low temperature; and therefore, supposing the space to be saturated with vapour when the thermometer stands at 90°, the fall of 5° or 10° in the temperature would force a portion of these vapours to return in drops or otherwise to the earth, until the quantity corresponds with the new state of the atmosphere. They possess the property of adhering to bodies which are colder than the surrounding atmosphere, and appear then in drops of water. There is however no necessity for the intervention of a third body; and the atmosphere, as soon as the temperature falls, deposits aqueous vapours in the form of dew. Such a fall in the temperature generally takes place about sunrise and sunset; and we find therefore the atmospheric moisture adhering in drops to the grass and trees. Our knowledge of dew has been chiefly derived from the investigations of Dr. Wells. His experiments confirmed the opinion of the ancients, that dew appears most on calm and clear nights. When the nights prove cloudy and windy, dew does not occur; and if a change take place in the course of the night, from serene calm weather to a cloudy and stormy atmosphere, the dew which had been deposited in the previous state will disappear. In clear nights the thermometer will be observed universally to fall; but if the air does not possess sufficient moisture in suspension, no dew will descend; whence it is evident that the lower temperature during night is not the effect of dew. Clouds are considered to be formed by vapours in a condensed state. The modification of clouds, or that which expresses the same thing, the structure or manner of aggregation, depends upon the influence of certain constant laws, subjected to endless subordinate diversities. My limits will not permit me to enter into details in this meteorological question, I must therefore refer the curious to Mr. Luke Howard's ublication on this subject'. It appears that electricity exercises a very marked action upon the figure and the height of clouds. The condensed vapour which composes the cloud cannot remain suspended in the air for any length of time. If the temperature increases, the cloud dissolves; but if it should fall, the vapour does not dissolve, nor can the cloud keep itself in suspension; and an aqueous deposition. takes place. That degree of temperature at which air containing some moisture is just saturated, is called the dew-point. If it should fall below this point, the vapours cannot exist any longer in the given space, for reasons which have been stated; and according as the temperature of the body of air differs considerably or only slightly from the dew-point, a fog or rain will be the result; and it depends further on the state of the atmosphere whether these aqueous deposits form fog or rain, sleet or snow. 1 See Philosophical Magazine, vol. xvi. pp. 97, 344; xvii. p. 5. |