Imágenes de páginas
PDF
EPUB

If we abstract from the local situation and circumstances of the place, the temperature will be expressed with tolerable accuracy by a formula first proposed by the celebrated astronomer Mayer. Let I denote the fine of the latitude; then the medium annual temperature will be 84–53°x 4 by Farenheit's scale. Hence the increment of temperature corresponding to one degree's advance to the equator is equal to the fine of double the latitude. Between the tropics the variation of temperature is : small; it is greatest at the latitude of 45°, and again diminishes as we approach to the pole.' It scarcely ever freezes in lower, latitudes than 35°, unless in very elevated places, nor hails in higher latitudes than 60°. Between the tropics the difference is small between the heat of summer and winter; it constantly increases as we advance towards the poles. In general it may be denoted by the formula 5° + 25°xls. The coldest season is in the middle of January, the hottest in July. The monthly variation of temperature is very irregular, and cannot be well ascertained. In general the summer and winter are pretty unie

form, and the greatest variation takes place in the spring and i autumn,

But the standard of temperature is variously modified from the nature of the soil, its elevation, its distance from the ocean, &c. When the air is cloudy it receives heat from the absorption of the solar rays; sometimes it derives a partial warmth from the condensation of vapours; but in general it participates of the temperature of the substances with which it is in contact. Water, from its superior density, absorbs the particles of light, and from its conducting quality becomes equally heated throughout. The superficial water, as it is heated, becomes specifically lighter and descends. Hence the temperature of lakes does not vary so much as that of the surrounding atmosphere. When the air was at 81', the water at the surface of the lake of Geneva was 62°, and at the depth of 87 feet 55°. In seas and in the ocean the variation is still less. The gulf of Bothnia differs confiderably from the temperature of the ocean, being some. times heated in summer to 70°, and commonly frozen in winter. The German sea is about 5 degrees warmer in summer, and 3 degrees colder in winter, than the Atlantic. The Mediterranean is in general warmer than the Atlantic. . · Earth receives heat from the sun more readily than water, but conducts it slowly. Befides, the light is spent in heating only the surface of the land, while it is nearly equally diffused through. great bodies of water. In the neighbourhood of Marfeilles the land is often heated to 160°, when the sea is only 77o. In win-, ter the earth is sometimes cooled to 14o, while the sea is 44o.

. . In

In general, the land is 10° hotter in summer than the surrounding sea, and as much colder in winter. · The great source of cold is evaporation. Hence a firm clayey foil, retaining closely the moisture, does not readily lose the heat which it has acquired. In stones or fand, on the con. frary, the moisture being extremely divided and diffused, is quickly evaporated. Hence the intense cold of Terra del Fuego, Living vegetables, by their perspiration, prodigiously aflist evaporation. Tall impenetrable forests, besides excluding the solar rays, are thus the active causes of cold. In Guyana in South, America, that part of the country which was lately cleared, is excessively hot; while in the wooded parts the inhabitants are obliged to light a fire every night. Cold is increased by every circumstance that promotes the solution of water in the atmosphere; by the heat of the air ; by its density; by its dryness, by its motion, &c. Hence the astoniving effects of dry winds; as the Sirocco, Harmattan, &c. Lofty mountains are exposed to the aerial motions, and liable to suffer evaporation ; at the same time that the solar rays, falling obliquely, excite little heat. The summits of mountains, however, are, from their communication with the mass of the earth, generally warmer than the air at the . same altitude ; and hence the winds generally tend towards them. As these ascend the sides of the mountains, they become rarer, deposit their moisture, and form fog; when they again descend, thev greedily reabsorb the moisture from the plains, Hence the effect of mountains in cooling the adjacent country, Even under the equator, and in summer, the mountains are, at the altitude of 16,000 feet, covered with snow. This is called the lower point of congelation. No vapour can rise higher than 28,000 feet; and this is termed the highest point of congelation. As we advance to the poles, the curve of perpetual congelation approaches to the surface. In general, if d denote the excess of the annual temperature above 32', the lower point of congelation will be at the altitude of dx 320 feet, and the higher at dx600. The effect of elevation in reducing the mediuni temperature, cannot be accurately ascertained. If the ascent be at the rate of six feet in the mile, of a degree may be allowed for every 200 feet of altitude ; if at the rate of 15 feet, half a degree may be allowed. Inands, participating of the temperature of the surrounding ocean, enjoy a milder climate than continents. The equatorial regions are cooled by the sea breezes ; but the higher latitudes derive additional warmth from the proximity of the ocean. .

Our ingenious author proceeds to examine the observations that have been made at various places, and to assign the causes which have occasioned the deviations from the standard of tem4.

perature.

perature. The coast of Africa feems to be the hottest part of the globe. The air in the shade in Senegal is commonly 94', and in the day tiine often 111°. In the interior parts of Asia, in Siberia and Grand Tartary, every circumstance contributes to produce intense cold. The land is extremely elevated, at an immense distance from the ocean, and covered with extensive forests. Hence it is perhaps the chilleft and the most inhofpitable region upon the face of the globe. The temperature of America is in general 10° or 12° below the standard. In fummer the heat is often excessive, but in winter the most intense cold is felt. The north-west parts of the continent are lofty, barren, and mountainous; to the eastward are numerous and magnificent lakes, the lower country abounding in swamps and morasses, and covered with forests. Cultivation will therefore contribute, in some degree, to ameliorate the climate, as well as to improve the scanty soil.

The author concludes with some remarks upon the causes of unusual cold in Europe : these, however, are, in our opinion, vague and indetermined. Our respect for the philosophical'au- . thor elevates him much above our verbal criticism. We have , given an abstract of his facts and reasonings, and have ventured, in some instances, to generalise and extend them. Upon the whole, Mr. Kirwan deserves the highest praise for the industry and . ability with which he has treated this new but important subject.

ART. III. Chemical Experiments and Opinions. Extracted from

a Work published in the last Century. " 8vo. 2s.6d. Prince,

Oxford; Murray, London. 1790.
AFTER the progress of science is advanced, we are inclined

to pause for a moment, and look back upon the labours of our predecessors. We are then able to select the bright ideas which lie buried in the chaos of exploded opinions, and to estimate their real value and importance. The little jealousies which disturb the human breast are foothed into a calm, and we are disposed, from pure benevolence, to venerate the worth and genius of a past age. The modern discoveries upon the subject of gases, are fplendid and important; they throw light upon chemistry and physiology, and contribute to the convenience and support of life. But these would appear to us as still in their infancy, and the creation of yesterday. We are surprised to find a philofó pher of the last century pursue the fame tract of investigation, and make several of the fame discoveries. At the fight of the representation of Mayow's pneumatic apparatus annexed to this

pamphlet, a certain northern profeffor' (we suppose the cele. brated Dr. Black) lifted up his hands in complete astonishment.' The name of Mayow is now rescued from oblivion,

and

and muft henceforth be ranked with Bacon and with Boyle.

He threw away with scorn the vague ideas annexed by the old ' chemists to the terms sulphur, mercury, &c. He has clearly

presented the notion of phlogiston, which rendered the name • of Stahl so celebrated. He perceived the action of dephlo! gisticated air in almost all the wide extent of its influence; he I was acquainted with the composition of the atmosphere, and

contrived to make the mixture of nitrous and atmospherical « air. He was well aware of the cause of the increase of weight. ? in the metallic calces, and distinctly asserted that certain bales " are rendered acid by the accession of nitro-atmospherical par(ticles, or what has since been denominated the acidifying prin

ciple. He discovered the method of producing factitious gas, 6 and observed its permanent elasticity; and, what is still more , strange,' he invented the nice art of transferring it from vessel

to vestel. The doctrine of respiration is all his own. He has ( carried on his investigation of this function from the diminu(tion of the air by the breathing of animals (as well as the

burning of bodies) to the change it produces in the blood dur! ing its passage through the lungs, and the use of the placenta.'. A genius so bold, so successful, and so extraordinary, mightily railes our curiosity and gratitude. Dr. Beddoes, with whose abilities the public is well acquainted from his elegant translation of Bergman and Spallanzani, endeavours, in a spirited introduction, to collect so.ne particulars with regard to the life of Mayow. He was born in 1645, and was admitted a scholar of Wadham College at the age of 16. He had made his principal discoveries before the age of twenty-three. He thone bright for a time, but was soon extinguished. He died in an apothecary's house near Covent-Garden in 1679, at the age of 34.

This pamphlet contains a translation of the contents of Mayow's treatises, together with an analysis. We are astonished to observe the extent and boldness of his inquiries. There is scarcely a phenomenon in nature which he has not ventured to explain. He seems to have been led into his speculations by the confideration of the formation of nitre. This falt derives its alkali from the earth; its acid from the air, and from that portion of the atmosphere which he terms fire-air or nitroatmospherical. The motion of these aerial particles occasions combustion. Hence the deflagration of nitre, and the current of air directed to burning bodies. He conceives that the alkali found in the ashes of vegetables arises from the decomposition of the nitre which they contained. The nitro-atmofpherical particles pass into the blood during respiration, and communicate warmth and the florid colour. He imagines that the

umbilical

Y a phenome extent and 6), an analysis, the com

umbilical arteries carry to the foetus, not only the nutricious juice, but also nitro-aerial particles, and thus supplies the want of respiration. The same remark he extends to chicken of an egg. . We must observe, however, that Mayow is strongly tinctured with the prejudices of his age. Like a sanguine theorist, he fondly imagines that his nitro-aerial principle is the grand mover in nature. He applies it to the explanation of solidity and elasticity; to that of the phenomena of water-spouts, thunder, and light, and colours. A lucid idea occasionally bursts out of a crowd of wild and extravagant notions, and it requires an attention to the late discoveries to appreciate his true merit. - We cannot conclude without mentioning an important experiment which Dr. Beddoes slightly announces. Nitrous acid has been procured by transmitting dephlogisticated air from Manganese along with atmospherical through a heated tube.

Art. IV. On the Confideration due to the Clergy from their Im.

portance in Society; a Sermon preached at the Anniversary Meeting of the Sons of the Clergy of Pembrokeshire, on Tuesday June 20, 1789, in the Parish Church of St. Mary, Haverfordwest. By Charles Symmonds, B D. Rettor of Narbeth. Printed for the

Charity, by Ross of Carmarthen. 4to. is. Williams, Lon· don. 1790.

IN this elegant composition the reverend author, after shew

ing the different ranks necessary in a state of civil society, and how much the existence of all depends on the due support of each, enters into an inquiry in what rank the priesthood should be held. In doing this, he presents us with an historical deduction of the sacred character, from the earliest ages to the state in which we now see it.

In the first ages,' observes our author, ( the sacred was in. separable from the royal character, the patriarch was the priest r as well as king. This leads him to describe the honorary distinction conferred by God himfelf on the order, which continued as long as the Jewish dispensation lasted. When this gave way to an improved system, the condition of the priesthood was only apparently changed. With its splendid trappings it loft no part of its dignity. Though he refused his direct fanction to any particular form of church government, the blessed Founder of our religion suggested the establishment of a priesthood, of different degrees, by his first delegation of the twelve, and by his subsequent one of the seventy disciples.

Our author gives next a very beautiful description of the . fimplicity observable in the early ages of the Christian church,

dignified

« AnteriorContinuar »