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mensions of the glass, the heat pro- radiating more abundantly, and absortceeding from the external atmosphere. ing little, suffers a depression of temThe portion of the glass, therefore, perature. The glass, therefore, precovered by the tin foil, becomes colder sented a cold surface to the air contithan any other part of the pane, and guous to it, and reduced the temperathe tin foil itself receives the same tem- ture of that air, until it attained that perature, which is not reduced by the temperature at which it was below a effect of the radiation of objects in the state of saturation with respect to the room, because the tin foil itself is a vapour with which it was charged; a good reflector of heat, and a bad ab- deposition of vapour, therefore took F sorber. Hence the tin foil presents a place on the glass.” colder surface to the atmosphere of the
This observation of Dufay was room than any other part of the sur- attended with no practical result
, but face of the pane, and, consequently, was considered as merely an interreceives a more abundant deposition of esting experiment, until Dr. Well's ice.
attention was drawn to it; and be If a body, which is a good radiator perceived in it a foundation for exof heat, be exposed in a situation where plaining the mode in which dew is other good radiators are not present, it formed. The vulgar notion relative to will have a tendency to fall in its tem- the formation of dew is, that moisture perature below the temperature of the is deposited from the air in consequence surrounding medium ; because, in this of the coldness of night, which was case, while it loses heat by its own the opinion held by Aristotle, who also radiation, its absorbing power is not remarks that it seldom appears but on satisfied by a corresponding supply of clear nights. Now the fallacy of this heat from other objects. A clear sky, mode of explanation will be sufficientiy in the absence of the sun, has scarcely apparent if we consider that the cause any sensible radiation of heat : if, there of the deposition of moisture on any fore, a good radiator be exposed to the substance, must arise from a difference in aspect of an unclouded firmament at between its temperature and that of the night, it will lose heat considerably by adjacent air : when a glass of cold water its own radiation, and will receive no is brought into a room, it must have corresponding portion from the radi- been often remarked that its surface is ation of the firmament to repair this covered immediately with moisture, loss, and its temperature consequently but if the water be warm, no such will fall.
deposition takes place. This fact "A curious experiment made by alone is sufficient to prove that there Dufay affords a striking illustration of could be no dew unless those subthis fact. He exposed a glass cup, stances on which it is deposited were placed in a silver basin, to the atmos- colder than the external air : now as phere during a cold night, and he found they are freely exposed, how does it in the morning a copious deposition of arise that they become colder than the moisture on the glass, while the silver adjacent air? Dr. Wells explained vessel remained perfectly dry. He this most satisfactorily by a series of next reversed the experiment, and ex observations and experiments, by which posed a silver cup in a glass basin. The he proved the formation of dew to arise result was the same: the glass was still from the radiation of heat from the sarcovered with moisture, and the metal face of the earth. He observed that free from it. Now metal is a bad radi. dew is deposited only during clear ator of heat, and, consequently, has a nights, when there are no clouds intertendency to preserve its temperature. posed to prevent the radiation of the Glass is a much better radiator, and has, heat into free space, or to reflect back therefore a tendency to lose its tempe- the heat given off from the surface of rature. These vessels being exposed the earth. On exposing substances to the aspect of a clear sky, received whose radiating powers were different, no considerable rays of heat to supply to a clear and cloudless sky, he found the loss sustained by their radiation. that quantities of dew were deposited This loss in the metal was inconsidera- on each of them proportional to their ble; and, therefore, it maintained its several dispositions to give heat: when temperature nearly or altogether equal he exposed wool, wood, glass, metal to that of the air; the glass, however, &c. he found that the metal acquired
the least dew, which accords with what night chosen was clear and cloudless. we have stated relative to the radiating Hence we see that the true object of power of metallic surfaces, and also covering tender plants during cold serves to explain the experiment of weather is not to prevent their suffering Dufay, just mentioned, wherein the glass from the cold of the adjacent air, but vessel was found covered with dew, to prevent the loss of heat by radiation. while the silver was quite free from We also can now understand the reamoisture. The reason why it seldom son why plants will be effectually profreezes on cloudy nights, and that ge- tected by snow, which prevents their nerally a clear moonlight, or bright attaining a lower temperature than starry night was formerly thought pro- freezing water, by protecting them from ductive of cold, is therefore apparent the effects of radiation. from this admirable theory of Dr. Wells, We shall conclude this short sketch who also observed that the temperature of some of the phenomena of radiaof the earth was sensibly raised by the tion by explaining the process of prointerposition of clouds during a clear curing ice in Bengal
, in which upwards night, and immediately lowered on their of three hundred persons are conpassing away from that portion of the stantly employed. We wish to obheavens over the place chosen as the serve that a different solution of the subject of examination. We shall process was formerly given by Dr. conclude this part of our subject by a Black ; but as it is now understood to quotation from Dr. Wells' Essay rela- depend on the same principle as the tive to the radiation of heat from the formation of dew, and has been satissurface of the earth.
factorily accounted for by Dr. Wells, “ I had often smiled in the pride of by the theory of radiation--we think half knowledge at the means employed it necessary to do more than merely by gardeners to protect plants from advert to the former erroneous explacold, as it appeared to me impossible nation. We shall extract Dr. Lardthat a thin mat, or any such flimsy co- ner's account of the mode of its forvering could prevent them from attain- mation. ing the temperature of the atmosphere, “A position is selected where the by which alone I thought them liable ground' is not exposed to the radiation to be injured. But when I had learned of surrounding objects: a quantity of that bodies on the surface of the earth dry straw being strewed on the ground, became, during a still and serene night, water is placed in flat unvarnished colder than the atmosphere, by radiat- earthen pans, so as to expose an extening their heat to the heavens, I per- sive surface to the heavens; the straw ceived immediately a just reason for the being a bad conductor of heat, interpractice I had before deemed useless. cepts all supply of heat which the Being desirous of acquiring some pre-water might receive from the ground ; cise information on this subject, I fixed and the porous nature of the pans allowperpendicularly in the earth of a grass ing a portion of the water to penetrate plot, four small sticks, and over their them, produces a rapid evaporation, by upper extremities, which were six which a considerable quantity of the inches above the grass, and formed the heat of the water is carried off in the sides of a square, whose sides were two latent state with the vapour. At the feet long, I drew tightly a very thin same time, the surface of the water cambric handkerchief. In this disposi- radiates heat upwards, while it receives tion of things, therefore, nothing ex- no corresponding supply from any other isted to prevent the free passage of air radiator above it. Tħus heat is disfrom the exposed grass to that which missed by evaporation and radiation ; was sheltered, except the four sticks, and, at the same time, there is no corand there was no substance to radiate responding supply received either from downwards except the cambric hand- the earth below, or from the heavens kerchief.” On examination of the grass above. The temperature of the water thus sheltered it was found to have ex- contained in the pans is thus gradually actly the same temperature as the ad- diminished, and at length attains the jacent air, while the ground unsheltered freezing point. In the morning the was found to be considerably colder, water is found frozen in the pans; it is having given off its heat, which was not then collected and placed in caves surreflected back by any awning, as the rounded with straw, which being a bad
conductor of heat, prevents any com- sacrifice of scientific accuracy, or that munication of heat from without by simplicity which is the object sought which the ice might be liquefied. In to be attained in all the volumes of the this way ice may be preserved during Cabinet Cyclopedia. If we might inthe hottest seasons, for the purposes of dulge the hope that the imperfect use or luxury.*
sketch here given of a part of this subWe have now considered a few of ject was acceptable to our readers we the subjects contained in Dr. Lardners would, at some future period, perhaps most useful volume and regret that the when the “ Dog Star rages," consider nature of our publication has prevented that highly interesting phenomena afour entering as minutely as we could forded by the cooling processes of wish into the several parts of it: we nature. have been necessarily obliged to pass We must now conclude these few over very superficially even those remarks on one of nature's most active branches of our subject of which we and necessary agents ; one on which undertook the consideration, and to the very form of existence depends, as omit all notice of some of the most we find that heat regulates the state of important subjects connected with this all bodies, as the most solid may be branch of science. We have not n- rendered fluid or aeriform by great adtered upon the subjects of specific heat ditions of heat, and vice versa, that all which led to some of the most impor- aeriform matter, by the abstraction of tant improvements in the steam en- heat may be rendered liquid or solid, gine, nor evaporation, ebullition, or being thus led “ to regard heat as one hiquefaction: those who wish for infor- of the great maintaining power of the mation of these most useful and im- universe ; and to attach to all its laws portant topics we refer to the seve- and relations a degree of importance ral chapters of Dr. Lardner's work, which may justly entitle them to the where they will find them explained most assiduous enquiry." clearly and perspicuously, without any
• That the process of procuring ice at Bengal, does not depend solely on the cold produced by evaporation, as was supposed by Dr. Black, and has been assumed as the true explanation of Mr. Lunn in his treatise in the Encyclopædia Metropolitana, but on the reduction of temperature produced by radiation, will be quite evident, if we consider merely the facts detailed relative to the process ; it is mentioned by Mr. Williams in his account of the formation of ice, that the nights on which it is procured, are clear and calm, and that the straw on which the earthenware pans are placed must be quite dry; now wind would encrease the evaporation, and wetting the straw would also diminish the temperature, if evaporation were the cause of the congelation; it is consequently quite evident, that though evaporation may assist the process, yet that it is not at all a principal cause of the production of the ice.
FAMILIAR EPISTLES FROM LONDON.
ADVANTAGES OF MAIL COACH TRAVELLING-RETROSPECTION AND SENTIMENTA
LITY—IMPROVEMENTS IN LONDON—DIFFICULTY OF GETTING OUT OF LONDON -TAKING LODGINGS— POLITICS-THE QUARTERLY REVIEW-THE REFORMED
My dear O'Brien
it brought to my mind and heart of byeI arrived here about three weeks ago gone times was more than my stoicism by the mail. It was not my will that was able to master, and though I consented to this mode of travelling ; clenched my teeth, and muttered psha but remittances had not come, and with my lips, it would not do, and I shed when one cannot have one's own vehi- tears. Five hours before I would cular convenience and post horses, the have deemed this utterly impossible, next resource for a gentleman, who but there is nothing of which we know wishes to keep moving, is his Majesty's so little, till the occasion comes, as our mail. There is a despatch about it, own feelings. Do you remember and precision, and consequence, and O'Brien -to be sure you do; that high prices, which most favourably glorious summer evening, when you distinguish it from its cheap and nasty and I, and poor George, made our first competitors on the road, with their entry into this mighty city. What exheavy luggage outside, and heavy vul- citement of spirits-what wonder and garity within. I was accidentally forced expectation we felt, and what bursts of to make use of one of them about six joyous gaiety from him, the youngest months ago, and found myself jammed and liveliest of the three, who now in between three gross looking per- withers in the grave! but I'll not think sons with horribly fat knees, who of this. had boiled ham and biscuits in their The mail from Spasses by the pockets, talked radicalism until dusk, end of the road where old Lady C. and then drew on red night-caps, and and Ellen lived, and where we have so began the most abominable snoring. I often walked together, and spent hapfelt exceedingly tempted to cut their pier evenings than I shall ever spend throats, but was deterred by consider- again. I have visited the old lady's ations of cleanliness. I made up my grave, and I have seen Ellen, aye mind, however, that for the future nó Ellen herself, and her husband! They consideration or necessity, short of have a monstrous fine house and a whole reaching some old gentleman or lady retinue of servants, but no children, already in extremis, who was likely to for which I felt-God forgive me, leave me an estate, should induce me something like gladness, or gratificato embark in a coach that was not the tion, or I know not what. Either there King's, or my own, for the time being. is a lurking fiendishness in our nature,
Although years and the world have or I am a bad specimen of humanity pretty well worn away the excessive-settle it how you will. I was at all tendency to the pensive, or tearful, or events glad to get out of the house dhrimmindhru frame of mind, which again, for when I saw that face, though in my early youth made me waste my it is not what it was, and heard that precious time upon bad poetry and voice which is less altered, though not worse flute-playing ; yet I confess to to my hearing the same, my heart was you that when I approached London wrung, and I could with difficulty once more, the vivid recollections maintain the steady cold composure,
which I would have died on the spot tain it, and got me away to the Regent's rather than have lost. But I did main- Park to walk and think.
“ Ye winged hours that o'er us past,
Enraptured more, the more enjoyed,
And not a wish to gild the gloom!"
signed, and nearly completed under the There are wonderful changes, and Tory Government. The Whigs would what is still more wonderful in these have been afraid to have attempted days, great improvements in the geo- them, because all the money they have graphy of our "ancient neighbourhood” cost, and it is no trifle, has been given since we were here five years ago. to bricklayers, and carpenters, and When I walked forth from the Salopian Jabourers. The Whigs want so much in the morning, and looked up for the for their own hangers-on, that they old Golden Cross Inn, where we used cannot ask for money to be employed to go to bed to feast the fleas, and listen in this way. to the rattling of coaches, and do with But I have forgotten to tell you of out sleep; lo! it was clean gone—not the other improvements to the westa vestige of it there, more than if it ward in the same neighbourhood.had never been. An immense space When you were here, Regent-street now laid open behind the statue of was the “ New-street," and came down, Charles, with a fine sweep right and as you will recollect, directly upon the left to the Strand and Pall Mall. The front of Carlton House. That fine houses of St. Martin's Lane, from the House with its beautiful portico and Church down to the Strand, are swept screen towards Pall Mall
, has been away, and a fine new range has been carried away, every stick and stone of built, terminating with the beautiful it, and the line of Regent-street now portico of the Church. By the bye a continues right forward to St. James's great dispute has lately arisen about Park, to which you descend by a fight this portico, which a certain modest of steps; a plain lofty pillar has been architect who designed the London raised to the memory of the Duke of University (so called) says is not beau- York; and on each side, ranges of tiful at all, except in the eyes of the magnificent houses, with plots of ornavulgar. This assertion is equally mental ground between them, and the idiotic and impudent, and the man who back of the houses in Pall Mall occupy has made it is laughed at for his pains. the old site of the gardens of Carlton This new range forms the right hand House. Descending into the Park, boundary of the space I have just told still more improvements present themyou of, when you look from White- selves. The interior, which you may hall, and the ‘Union Club-house and remember was a huge field, occupied the College of Physicians form the generally by sorry-looking cows, a left; so you may judge how wide it is. sluggish canal in the centre, and a In depth it extends northward to the shabby wooden paling for the circunKing's Mews, which they say is to be ference, is turned into an ornamental pulled down, and a National Gallery planted enclosure. Well-cut walks for paintings and sculpture built on the lead round a fine piece of water formed side. All the vile neighbourhood lying by widening and deepening the old between Chandos-street and the Strand canal, and round the whole there is an has been completely swept away, and open iron railing. Here scores of ped new streets 'made, forming various ple come to walk on week days, and openings into the Strand, which itself thousands on a Sunday. I am sorhas been widened from Charing-cross ry that the quiet and the shade of the to Bedford-street, and new houses built walk under the wall of the Carlton on the North side. All these valuable House garden is lost, and monstrous