densation. In the third, reckoning from the tropics to the latitude of forty, the atmosphere may sometimes be suddenly condensed by currents of cold air from the north, and still more so in England. But the greatest variation must necessarily take place on the continent to the northward, where, during the summer, the weather is as hot as within the tropics; and, in winter, the thermometer, for many weeks, continues several degrees below the freezing point. "The thermometer also, which measures the degree of heat in the air near the earth, will contribute towards denoting when changes are likely to take place in the lower regions of the atmosphere; the hygrometer distinguishes the quantity of moisture in the atmosphere, and the electrometer will point out the quantity of electricity which prevails in it. "The words generally engraven on the plates of the barometer rather serve to mislead than to inform, for the changes of the weather depend rather on the rising and falling of the mercury, than on its standing at any particular height. When the mercury is as high as fair, or at thirty degrees, and the surface of it is concave, beginning to descend, it very often rains; and on the contrary, when even the is at twenty-nine mercury degrees, opposite to rain, when the surface of it is convex, beginning to rise, fair weather may be expected. These circumstances not being known, or not duly attended to, is the principal cause that farmers and others have not a proper confidence in this instru commonly early in the morning, or late in the evening, than at noon, which seems occasioned by the obvious causes of the atmosphere being condensed by the cold of the night, and rarefied by the heat of the day. "The following observations of Mr. Patrick seem confirmed by experience. 1. The rising of the mercury presages, in general, fair weather, and its falling foul weather, as rain, snow, high winds, and storms. "2. In very hot weather the fall of the mercury indicates thunder. 3. In winter the rising presages frost; and in frosty weather, if the mercury falls three or four divisions, there will certainly fol low a thaw; but in a continued frost, if the mercury rises, it will certainly snow. "4. When foul weather happens soon after the falling of the mercury, expect but little of it; and, on the contrary, expect but little fair weather when it proves fair shortly after the mercury has risen. "5. In foul weather, when the mercury rises much and high, and so continues for two or three days before the foul weather is quite over, then expect a continuance of fair weather to follow. 6. In fair weather, when the mercury falls much and low, and thus continues for two or three days before the rain comes on, then expect a great deal of wet, and probably high winds. ." 7. The unsettled motion of the mercury denotes uncertain and changeable weather. "But to these remarks may be added, that, when the barometer suddenly falls two or three tenths, without any material alteration in K the t the thermometer, and the hygrometer is not much turned towards moist, a violent gale of wind may be expected. When the hygrometer inclines far towards moist, with only a trifling descent in the barometer, it denotes a passing shower and little wind; and when the barometer falls considerably, and the hygrometer turns much towards moist, the thermometer remaining stationary, and rather inclined to rise than fall, both violent wind and rain are likely to follow in the course of a few hours. « General or common Prognostics of the Weather. Amongst these we may reckon such as are derived from birds, beasts, insects, reptiles, and plants; to which might be added great part of the wood-work in houses, as doors, windows, window-shutters, &c. "Birds in general retain in the quill-part of their feathers a quantity of oil; which, when they feel an extraordinary degree of moisture in the atmosphere, they express, by means of their bills, and distribute it over their feathers, to secure their bodies against the effects of an approaching shower. "Swallows, in pursuit of the flies and insects on which they prey, keep near the earth in wet weather; and in dry weather, from the same cause, they fly much higher. "Domestic animals, as cows and sheep, but particularly the latter, on the approach of rain, feed with great avidity in the open field, and retire near the trees and hedges as soon as they are satisfied. In fine weather they graze and lounge about, eating and resting alternately with apparent indifference. "The pimpernel, commonly called peep-a-day, or shepherd's weather-glass, closes its leaves before rain; and the down of the dandelion is much affected by moisture. "All wood, even the hardest and most solid, swells in moist weather. The vapours insinuate themselves into the pores of trees, and also into the wood-work of houses. "Insects and reptiles of all kinds seek or avoid rain according to their respective habits, by these means giving notice of every change of weather. Dur "It is a well-known fact, that before rain, particularly in summer, a strong smell is perceived from drains and common sewers, as well as from every other body emitting a great quantity of effluvia. ing fair weather, even in summer, the atmosphere readily absorbs all the vapours and exhalations from the earth until it is completely saturated, and consequently the effluvia from the bodies which emit them will then be confined and ascend in a narrow compass, like the smoke of a chimney in dry weather, almost perpendicularly; but when the air is saturated with moisture, and becomes rarefied and expanded, as it always does before rain, the volume of air containing the effluvia will be extended ho rizontally, and diverge from these different bodies as from a centre, and will be sensibly perceived on all sides, but will of course be most perceptible on that to which the current of air or wind moves. "In winter, when the thermometer is between thirty-four and forty degrees, the air being in a state of condensation, and the running water being warmer than the land, a mist or fog may be seen rising above the river, particularly when the air is cold and clear; but this [147] BLIGHT ing them variously. On BLIGHTS. [From the same Work.] LIGHTS are diseases in cident to plants, but affectIn some the leaves only are withered, in others the leaves and blossoms; some do not lose much either of their colour or shape, others again seem shrivelled or scorched, and very soon entirely perish. Some persons suppose, that blights come from the eastward, and others from the westward; and by many it is believed that they are frosts which descend from the upper regions of the atmosphere. Insects are often found on the trees which have suffered from blights, whence it is also imagined that some kinds of -blights proceed from immense number of insects, which are bred in particular places, and are transported by the winds towards the plants which they destroy. Experience confirms the exist ence of almost all these different blights. We will offer a few conjectures on the subject, and attempt to explain from what causes they are derived. "In the spring vegetation commences, and frequently in the month of April the peach and necLarine trees are in blossom. About But the same time, the earth being warmed by the return of the sun, the current of air will come in strong gusts from the ocean, and produce those winds, which are generally known by the name of the equinoxial gales. The blossoms of those fruit-trees, therefore, which are not sheltered towards the westward, will be blown off before the fruit is formed, and produce those blights which affect the blossoms and not the leaves. the current of air which comes from the eastward about the same season, being excessively dry, absorbs all the moisture, both on the leaves and fruit, and produces that parching kind of blight which curls up the leaves and destroys trees themselves. When the leaves the fruit, and sometimes kills the them is broken, the perspirable are parched, and the texture of matter becomes viscous, and by adhering to the leaves affords both shelter and nutriment to insects. When the young are hatched, they begin to prey upon the leaves, and time will ultimately destroy the if they are not removed in due flexions from observations made in trees. I was led to make these re K 2 my my own garden for seven years -successively. On the north side of it is a stone wall, coped with brick, of one hundred and thirty yards in length and twelve feet high. Against this wall are planted eighteen peach and nectarine trees, one Cressan pear, and two or three small vines, kept very closely pruned. The trees are planted in a border of four feet in breadth, on a soil of loam and black earth, of about twenty inches depth, on a gravel. The soil is nearly the same as the rest of the gardens in the valley near Cardiff. The wall is built of the same mate-rials, of the same height, and its aspect corresponds nearly with that of other gardens, being about S. by W. or S. S. W.; and the trees are pruned by the same person who works for many other families in the neighbourhood. Nevertheless, when their trees entirely fail, these have borne regularly every year four times as much fruit as we choose to leave on the trees to ripen; and the fruit, so abundant, has likewise been of the best quality. The trees are about fourteen years old, and consist of the Magdalene, Rambouilet, Royal George, and Newington peaches, and the Prignon, Etronge; Murray, and Roman nectarines. It may be proper to observe, that no manure is used to these trees, but every year a small quantity of pure virgin earth is put on the border, which is also dug in a good spade deep, both in spring and both which my wall is sheltered, 1 am much disposed to conclude, that the blights from which they suffer are to be ascribed to those causes. "It sometimes happens that the nectarine-trees have been slightly attacked by a blight, and the peaches have escaped, though planted alternately with the latter on the same wall. As the blight parched and curled the leaves, I suppose that it came from the east in the manner above described; and it is probable, that this current of air attacked the leaves of the nectarines without injuring the peaches, on account of the superior delicacy of the leaves of the former, or perhaps from their being more porous, and suffering more from evaporation. This blight, however, has only once occurred; these remarks, therefore, are intended as mere suggestions or hints on the subject. If the nectarines should frequently suffer, and the peaches never, it may probably be ascribed to the different qualities of their leaves; but if the contrary should happen, we must then refer to some other cause. "A wall with a projecting coping is supposed to be favourable to fruit-trees, in protecting their leaves and blossoms from the descent of cold dews, which early in the spring are accompanied with frost; but this plan does not seem to me entirely free from objection; at least it appears necessary to have this a moveable fence, for when the danger of the frost is over, the descent of the dews are necessary to refresh the trees and swell the fruit, which will never come to perfection from being artificially watered. Besides in hot dry weather the expense of labour for this kind of work would be very heavy; the gardeners would not begin their work in due time; but even if we suppose them to be active and attentive, the absorbents of the leaves and fruit would take up ten times as much moisture in the course of the night, and early in the morning, as they would receive from the sprinkling of the water-pot throughout the whole day." ACCOUNT of the DISCOVERY of SILVER in HERLAND COPPER-MINE. By the Rev. MALACHY HITCHINS. Communicated by the Right Hon. Sir JOSEPH BANKS, Bart. K. B. P. R. S. [From the PHILOSOPHICAL TRANSACTIONS for the Year 1801. Part 1.} about seven miles N. E. of St. Michael's Mount, on the southern coast of Cornwall; and two miles and a half from the mouth of the river Hayle, on the northern coast of the same county: it is contiguous to Prince George mine. "It commences in a valley on the west, and passes through a hill, which is first of steep and then of moderate ascent, for upwards of half a mile eastward; when the principal copper lodes, which follow this direction, meet with a large cross lode, by which and by other cross courses and flookans, which intersect them in their further progress, they are repeatedly heaved, and so disordered by these heaves, in their form and position, and so changed by them, in respect to their composition, as hardly to be recognised. "The strata of the district in which this takes place, consist of the common metalliferous sort of argillaceous slate called killas. "The copper lodes of this district are remarkable for the shortness of their continuity: for, whereas other lodes may be traced to an indefinite extent in the same line of direction, these, on the conrary, are observed to taper away gradually, and terminate, to all appletely and irrecoverably. "This mine was worked about twenty years ago, when it was sunk to the depth of one hundred fathoms from the surface. It was again set to work about eight years. since; has now four fire-engines and two steam-whims on it; and is sunk to a depth of one hundred and fifty-five fathoms below the surface, or, as the miners call it, from grass. "It is in this latter period of its history, that a discovery has been made of a considerable quantity of silver ore, in a particular part of the mine, the singularity of which discovery, in this country, has much excited the curiosity of the public. "For, although the numerous veins of lead in Cornwall are richly impregnated with silver, and occasionally yield small quantities of silver ores, and even specimens of native silver, yet, hitherto, no instance had been known of their yielding this precious metal in such abundance; nor had any circumstances, in the natural history of the mineral veins of this country, borne any analogy to those which ac companied the present discovery. "These circumstances therefore, having been examined with K 3 more |