Imágenes de páginas
PDF
EPUB

ed like a cloud of more than ordinary magnitude, and probably very generally mistaken for such a cloud; from its southern portion, however, it emitted a fine brush of electrical light, which gradually stretched itself eastward, till it nearly reached the horizon, and, having continued in this situation for a short time, the whole mass slowly disappeared from the face of the sky.

I have been particular in describing these appearances for two reasons; because, in the first place, the phenomena themselves are rather of rare occurrence, and are, therefore, worthy of being recorded for the purpose of comparison with future appearances of the same kind. The Aurora itself is well known to be a phenomenon which only occurs after irregular intervals, sometimes of very considerable length; and the splendid meteor of the bow requires so many favourable circumstances for its exhibition, that we cannot wonder it should have been so seldom observed. It seems, indeed, that some old people in the north of England recollect to have seen such appearances in their younger days; but, for many years, the meteor had not been observed in this country, and when it again presented itself three years ago, even the best informed seemed to be equally struck with wonder at the beauty of the phenomenon itself, (for, next to the rainbow, it is certainly, of all meteorological appearances, the most magnificent,) and with astonishment at the little acquaintance they had previously had with it.

My chief inducement, however, in presenting to your readers the above particulars, was that of directing their attention to the following conclusion, namely, that though, when the phenomenon of the bow is exhibited, it seems to be distinguished by several of its properties from the usual characteristics of the matter of an Aurora, we are yet able to trace a series of appearances which serve most complete ly to connect these phenomena. Masses of electrical matter developed in the atmosphere are, in fact, of much more frequent occurrence than inattentive spectators are apt to believe. These appearances, indeed, are often altogether unnoticed, from their being

VOL. I.

merely regarded as brilliant clouds; but they exhibit, in fact, every variety of form, from that of a slight fleecy appearance, only to be distinguished by the most skilful eye from ordinary collections of buoyant vapour, to those beautiful phenomena which, under the form of the bow, are amongst the most magnificent appearances which the atmosphere presents. The indications of an Aurora, besides, are the unfailing attendants of such phenomena; frequently, when the Aurora becomes widely diffused, its most vivid corruscations occupy the situation where immediately before the bow had been observed; and every consideration serves to shew, that the matter which is employed in all these appearances is the same, and that its more rapid movement in the case of an Aurora, and the beautiful tints also by which it is characterized, are either the effect of its moving in a freer medium, or of its being developed in a less condensed and accumulated form.

Next to the splendour of the light itself, its beautiful regularity when in the form of a bow, will naturally attract the observation of the curious. There cannot, however, be any doubt, that the arched appearance which the bow assumes is merely an optical, though certainly a very pleasing illusion,-that it results entirely from our disposition to refer the phenomenon to the arched appearance which the heavenly vault itself assumes ;—and is to be explained in the same way in which Mr Dalton and Mr Cavendish have accounted for the similar form of the Aurora Borealis. From the demonstration of Mr Dalton, it is certain that the Aurora consists of a great number of straight cylinders parallel to each other, and to the dipping needle at the place where they are seen. The luminous arch, in the same manner, is merely to be considered as a great body of electrical matter, existing in a very condensed or insulated state, either parallel to the horizon of the place of observation, or developed obliquely from strata of air, which are, at the time, in the same state of electrical charge. To this obliquity it may perhaps sometimes be owing that one extremity of the arch seems to be of greater breadth than the other; that extremity subtending

Q

the greatest angle at the eye, which is developed from a stratum nearer the earth.

The variation of the magnetic needle during such appearances, is one of the most instructive of the circumstances which attend them; and from the following remarkable coincidences it will appear, that a needle may often indicate, by its variations, an uncommon state of atmospherical electricity at a considerable distance from the place of the observer,-in the same manner as the variations of the barometer are known to indicate storms and hurricanes which happen at the distance of many miles or leagues. The finest needle at present kept in Britain is probably that of Colonel Beaufoy; upon referring to the published account of the Colonel's observations for the period of the bow of September 1814, I find the following note: "September 12, variation remarkable, and the morning observation greater than the noon, for which no reason can be assigned. The weather was overcast, and the wind north, blowing at the rate of ten miles an hour." From this note it is evident that Colonel Beaufoy had not been aware of the meteorological appearances which were visible in the more northern parts of the island the evening before, as a knowledge of these appearances would infallibly have suggested to him the solution of the difficulty. With respect to the variations of the needle for September 26, 1815, on which occasion a bow was visible at London, though Colonel Beaufoy does not appear to have known of it, it appears that the variation for noon of that day was 24° 29′ 46′′, which is considerably above the mean variation for noon of that month. I have had no opportunity of consulting the variations of the needle about the time of the appearance of the bow of 1816, but I have no doubt that considerable irregularities will be found to have happened about that period. What I have already stated, however, is sufficient to prove not only that such variations do occur when the electricity of the atmosphere is remarkably agitated, (a fact which has been long ascertained,) but that the variations of the needle may indicate changes which are not directly experienced at the place of observation.

The electrical appearances I have now been describing, especially that

of the bow when in its greatest perfection, afford the best of all expedi ents for resolving a problem which is of considerable interest, namely, the average height at which the Aurora takes place. The method of ascertaining this, by means of the parallax of the bow, is well known to philosophers. Unfortunately, however, no such correct observations respecting its relative place in the heavens appear to have been made during the recent appearances, as to afford any sufficient data for determining this problem. In one instance, indeed, I know that such a measurement was made by a gentleman in the north of England, with respect to the bow of September 1814; but his data were confessedly inaccurate, and the result of his calculations was, that the height of the meteor was probably somewhat between six and eight miles. The Aurora itself, however, with which this phenomenon has a very intimate connection, has been placed (and probably correctly placed) at all distances, from sixty to eight hundred and one thousand miles; and, indeed, when we consider the vast space over which the meteors I have been describing were observed, (a space which seems to have embraced some hundred miles in every direction,) we shall readily allow, that their height must have been immensely greater than, from viewing their appearance, we might be disposed to believe; and that the accumulation and extent of matter which they contained, must have been proportionally enormous, to present so remarkable an appearance at so great a distance.

A law was long ago stated by Blagden, (in the Philosophical Transactions, I believe, for 1784,) respecting the order in which the electricity of the atmosphere is developed, which assigns the very highest regions of the air as the sphere appropriated to the phenomena we have been considering. According to this writer, those rapid and destructive exhibitions of this fluid, which are familiarly known to us under the denomination of lightning, are chiefly confined to the region of the clouds, that is, to the lower departments of the circumambient fluid. What we commonly denominate falling stars, are considered as more appropriate to that higher region in which the formation of vapour

is seldom perceived, though they may also sometimes descend into a lower sphere; while the highest regions are the scene of those appearances which the Aurora and its kindred phenomena exhibit. I apprehend that this account will be found to be substantially correct, though of course these different phenomena will often be seen to shift their situation according to the varying condition of the aerial strata; and I have only to add, that I apprehend a similar law takes place, in the order in which electrical phenomena are presented, as we advance from the equatorial towards the polar regions. It is well known, that the electrical appearance most frequent at the equator, is that of prodigious storms of thunder and lightning; in the serene regions of the temperate zone, (though here also storms of lightning occasionally occur,) the most common appearance which electricity assumes, is that of those gliding meteors which serve only to give additional beauty to the spangled glory of a southern sky; and it is not till we have advanced into those more terrific regions which surround the pole, that the Aurora is beheld in constant activity, and in the utmost magnificence it is capable of assuming. Whatever may be the value of these observations, one thing is certain, that a series of such appearances as I have now been describing, never fails to indicate a deranged state of the electricity of the air. We all know, accordingly, that the condition of the atmosphere, during the three last years, has been considerably different from its usual tenor; and the phenomena I have been discussing seem, therefore, worthy of being remarked, not only as materials of philosophical history, and as appearances in themselves of considerable interest and beauty, but as concomitants also of that very remarkable weather which has been one of the "signs" of these last eventful years, and which seems lately to have extended itself over a very considerable portion of the civilized globe. I am, yours respectfully,

Edinburgh, Sept. 3, 1817.

P.

OBSERVATIONS ON THE NATURAL HISTORY OF BIRDS.

MR EDITOR,

I HAVE read with no small degree of pleasure the Miscellaneous Obser

vations on Natural History, by your correspondent P. in your last number; and am convinced, that many facts and important remarks may be made known in that easy and familiar manner, which would not warrant an elahorate or scientific essay on the subject. For many years as a boy I was accustomed to travel to my parishschool, over a district of wild ́uncultivated country, extending for two or three miles; and when relieved from the more important duties of the day, our great amusement in the spring and summer months, was to ramble over that country in search of birds' nests. Now, Mr Editor, even in those days I was struck with many singular discoveries (for such I still consider them) in the economy of some birds, that I have not as yet seen explained, or even hinted at, in any scientific work which I have perused on the subject. I shall, therefore, trouble you with some of those observations which were made as a boy, and which I have often had an opportunity of confirming since.

To begin, Sir, with the Lapwing or Green-plover, (Tringa Vanellus.)

This bird, it is well known, generally deposits its eggs in low marshy ground. It is not at the trouble of building a nest, as I have never observed more than a small round hole scratched in some little eminence, with perhaps a few particles of fog or dried grass between the eggs and the moist earth. It lays four eggs; and what I have to remark as deserving of consideration is, that if the nest is discovered as soon as the bird has begun to lay, and you remove an egg, so as to allow only one or two to remain in the nest, the bird will continue to lay for ten or twelve days, nay, for weeks successively. If, however, you allow the number to reach four, it immediately begins to hatch, and there is no farther deposition of eggs; but if any of the eggs are then removed, that is, after the natural number has once been completed, it immediately forsakes the nest and prepares a new one. I have myself continued to remove the eggs for ten days at a time, and always found a fresh one every morning, and have often tried also to take away one after the ordinary number four had been completed, but always found the nest immediately forsaken.

I have tried the same experiment

120 Observations on the Commerce and Manufactures of Glasgow, &c. [Sept.

with the common Lark. If you allow only one or two eggs to remain in the nest, the bird will go on to lay for a time indefinite; but if they reach three the bird will hatch. The common number of eggs in a Lark's nest is five; but it will hatch with three.

I hope some of your readers will try to explain these facts upon rational principles. They have often puzzled me, more particularly as I have not seen them noticed in any work on the n tural history of birds. Here we have a bird, which, as soon as it has deposited four eggs in its nest, immediately ceases to produce any more, but if disturbed in its arrangements will go on to form five, perhaps ten times that number, and yet cease the moment it has collected its usual number for hatching in the same spot.

Is it any species of food which the hen bird uses? or can it be the impregnation of the male one, that keeps up this production of eggs, and the refraining from which causes the sudden cessation,-for sudden it must be considered, when it takes place in the course of twenty-four hours?

Birds that build well regulated nests, are very assiduous in their labour until the whole is completed. The male is, in general, the carrier of the materials, and the female the architect. Many a long hour have I watched the operations of the Blackbird and the Mavis, both of which build very elegant nests, and somewhat similar in their construction. These birds generally build on the banks of a running stream, either among the roots of the hazel-bush or in the decayed trunk of a tree. The first wall is composed of strong grass or the small branches of trees; these are again lined with a coating of fine clay: The Mavis is content with these two, but the Blackbird lines the clay with fine hair or wool, and altogether forms a most comfortable and warm abode for its young.

In former days, when cock-fighting was more in vogue than at present, the great desideratum was a gamecock that had been hatched by a Magpie. The being nursed by such a stepmother was considered as rendering the hero invincible. Yet no small degree of finesse was necessary to beguile the Pyet, and the being able to paint the hen's egg so as to

impose upon that wily bird, was considered an acquirement of no trifling consequence among the knowing ones of those days. If the Magpie discovered the egg, it was indignantly thrown out; but if the young bird was once hatched, she was even more attached to the stranger than to her own offspring. I have seen several game-cocks that first saw the light on the lofty summit of an old ash tree that grew in my father's kail-yard. They were certainly much more spirited, and, if I may be allowed the expression, more cruel than when hatched by their natural mother. Here, again, Mr Editor, we have a field for the speculations of the natural historian.-By the bye, if you disturb a Magpie in her operation of building, she will immediately remove the sticks she has collected to another branch of the same tree, but much lower down than the one she first occupied.

If you think these facts worth communicating to your readers, I shall have much pleasure in supplying you with several others not less interesting in the natural history of animals as well as birds. I am your sincere wellwisher,

Edinburgh, 4th Sept. 1817.

A.

STATISTICAL OBSERVATIONS ON THE COMMERCE AND MANUFACTURES OF GLASGOW, PAISLEY, GREENOCK, AND THE ADJACENT DISTRICTS.

MR EDITOR,

THE Commerce and manufactures which have their chief seat in the lower ward of Lanarkshire, in parts of the respective counties of Renfrew, Dumbarton, and Ayr, and of which the city of Glasgow may be deemed the centre and emporium, have evidently been attracted by local and natural pre-existing advantages.

The great river and firth of Clyde, situated on the western coast, and even more accessible from the Atlantic Ocean than the Mersey or the Severn, is peculiarly adapted for the convenient prosecution of that great commercial intercourse with the new hemisphere, of which Glasgow has become the principal Scottish depôt.

The circumstances which, united to the demands of external commerce, contributed to localise and to extend the manufacturing operations of these

1

1

1

districts, may be traced to the cheapness of the coal and iron, with which the whole adjacent country abounds, the number of the springs and waterfalls, and the low rate at which the wages of labour have been almost uniformly kept, partly by means of its own numerous population, and partly by an almost incessant influx of strangers from the Western Highlands, from Ireland, and generally from the whole surrounding counties.

From these physical advantages, the manufactures of this district unquestionably took their rise, and the same causes which first attracted seem likely to render them permanent. Indeed, it is apparent, that to a similar relative situation, and to the presence of the very same minerals, we must ascribe the local residence of the corresponding branches of industry, which have fixed themselves in Lancashire, Staffordshire, and Warwickshire; and which have given to Manchester and Birmingham, those extensive manufactures, and to Liverpool, that widespread commerce, which are now in some degree rivalled at Glasgow, Paisley, and Greenock.

The commerce of the Clyde began to extend rapidly only about the middle of the last century; and the first intercourse of great importance was that with the North American colonies, which now form the United States.

The exports were such manufactures as the country then afforded; and the returns were chiefly in tobacco, of which, at one time, more was brought into the Clyde than into any other British river, the Thames itself not excepted. The traffic was limited to few hands; and splendid fortunes were realized by some of the individuals who were engaged in it. It was, however, suspended by the war, which terminated in the separation of the colonies from the Parent State.

At the peace of 1788, the intercourse with America was re-opened, and has ever since formed a considerable branch of the commerce of the Clyde; subject only to the occasional suspensions produced by political contingencies, and to the more frequent stagnations arising from glutted markets.

The American trade since 1783 has been incomparably more general than formerly, both in its channels, and in its returns; and of the tobacco trade,

once so great, not more has reverted to the Clyde than its own natural proportion.

During the same period, the colonial traffic with the West Indies has progressively extended, with an uniformity, only casually interrupted by those events, which are common to every branch of extended commerce. Like that of America, it is now ramified and divided amongst a much greater number of mercantile houses and individuals, than in its earlier times; and is carried on with that mixture of success and misfortune, which is inseparable from extended commerce, and general competition.

A considerable trade certainly existed in the Clyde, before manufactures were much cultivated in Glasgow and the vicinity. But as the demand for the finer sorts increased with the opulence of the colonists, a stimulus to produce these upon the spot from whence they were exported was naturally and gradually created. A variety of manufactures, to emulate those of England, were consequently attempted; some of which proved abortive, whilst others were gradually matured and established. It was not, however, until about the close of the American contest, that a new manufacture was introduced; which, fostered in its infancy by a general revival of foreign commerce, has since incomparably exceeded all others, both in extent and in the investment of capital.

The cotton manufacture has indeed assumed so entirely the character of a staple, that, upon its prosperity or decline, the chief interests of the whole western districts are considered to depend. To analyze, therefore, in some degree, the nature, tendency, and operations of this new colossal, although depressed manufacture, will be admitted to be of paramount importance in every inquiry into the manufacturing state of Scotland.

The origin of the British manufacture of cotton goods must be traced to the invention of the spinning machinery. This wonderful mechanical improvement was introduced into Scotland at the very period alluded to; and various cotton-mills were erected, where waterfalls could be found sufficiently powerful to give motion to the extensive range of machinery which is required. These waterfalls

« AnteriorContinuar »