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which, in the state of nature, constitutes its epi- || ascent of the stalk, and descent of the radicle, dermis, and it has no power of forming this sub which seem to shew that gravitation is the prinstance, which there is good reason for supposing cipal cause of both these effects. The chief elementary. Mr. Davy gave an account of the diseases of the more perfect plants, he stated, are experiments which shew that carbonic acid is produced either by parasitical vegetables, or by absorbed and decomposed by plants in the solar insects. Wet seasons conduce most to the prolight, and oxygen evolved. He seemed inclined pagation of mildew or blight; and dry weather to doubt whether they ever evolved carbonic acid | to the increase of the turnip fly, and other analoin a state of health; and he mentioned some gous destructive insect tribes. facts, which seemed 10 shew, that the carbonic The eighth, and concluding Lecture of the acid which usually appears when plants are con course was upon the mode of the dissemination fined in darkness in close vessels, is really owing of seeds, and upon the progress of vegetation, in to the decay of some of their dead parts. The a state of nature. Rucks, according to Mr. Davy, epidermis, the heartwood, or a single yellow spot by their decomposition, form a soil; different in the leaf, would be fully adequate to such an species in very different periods; lichens and moseffect.
ses are their first productions, and lastly a mould The seventh Lecture was principally devoted is formed capable of supporting grasses. Peat, he to the consideration of the causes of germination considered, as chiefly arising from the destruction and the circumstances that affect the healths of of forests, exposed by the early cultivators of difplants. Mr. Davy stated that seeds were inca- |ferent countries, by thinning their outskirts. pable of germinating, unless supplied with heat, Mr. Davy made some general observations on the moisture, and air, and that oxygen is always ab nature of different soils, and recommended new sorbed in this process, and carbonic acid evolved. I inquiries on this subject as peculiarly important He mentioned Mr. Knight's experiments on the to the agriculture of the country.
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The famous Agrippa, in his treatise on the most learned French authors, Du Chesne, La vanity of the sciences, has collected many instan- || Latoreur, Chifflet, Fauchet, and Father Menesces of these marks of distinction; the Romans trier; according to Cambden, the use of family bore the eagle; the Phrygians, a hog; the Thra arms began among the English, as well as French, cians, a skeleton, or the figure of death; the just after the crusades, yet, if we may rely on the Goths, a bear; the Alans, 'hat invaded Spain, a learned Sir Henry Spelman, hereditary bearings cat; the old Franks, a Lion; and the antient were not generally established until the time of Saxons, a horse, which is still borne in the arms | Henry III. of England; for the last Earls of of his Britannick Majesty; but these marks were Chester, the two Quincies, Earls of Winchespromiscuously taken for hjeroglyphics, symbols, ter, and the two Lacies, Earls of Lincoln, still emblems, and personal devices, like the salaman- || varied the son from the father. As for the Scots der of Francis I. of France, and were not arms and Welch, they pretend to excel the English properly so called. Thus Pasquier tells us in his and French in ancient descents, and regular Recherches de la France, or inquiries into the armory ; but according to Father Menestrier, antiquities of France, lib. ii. p. 84. that before whose authority is esteemed of great weight in this Marius, the eagle was not the constant ensign of matter, Henry the Falconer, who was raised to the Roman Generals, who, in their standards bore the Imperial throne of the West in 920, by regusometimes a wolf, sometimes a leopard, or anlating the tournaments in Germany, gave occaeagle, according to the fancy of the chief cornman- sion to the establishment of family arms, or marks der. The like variety is observed in the arms of of honour, which undeniably are more antient, the King of France, and Great Britain, as we shall | and better observed among the Germans, than in mention hereafter, but the most learned authors | any other nation. Moreover, according to Father agree, that the hereditary arms of families, as well || Menestrier's opinion, with tournaments first came as their double names, or surnames, began no up coats of arms, which were a sort of livery, made sooner than the crusades, that is about the begin-up of several lists, fillets, or narrow pieces of stuff ning of the tenth century; and their opinions who of divers colours, from whence came the fefs, the trace them up higher is confuted by the best and "bend, the pale, the cheveron, the lozenge, &c. Na, XV. Vol. II.
which were the original of family arms; for they || figures and ornaments of the shields of Cavaliers, who never had been at tournaments, had not such as extravagancies. Menage, whose etymologies marks of distinction, although they were gen are forcibly dragged in, fetches the word, blazon, tlemen. They who inlisted themselves in the from the Latin latio, a bearing, by putting before crusades, for the conquest of the Holy Land, took it a b, because blazon denotes, “what's borne on up also armorial ensigns, particularly crosses of a shield.” Borell, hits it a little better, in deriv. divers colours, for distinction sake; before that ing it from two Latin words, viz. laus, praise, and time, that is, before the tenth or eleventh century, sonare, to resound; and, by putting a b before nothing is to be seen on the more antient tombs the entire word, out of that odd composition he but crosses and Gothic inscriptions, with the forms the barbarous verb, blausunare, from effigies of the person; the tomb-stone of Pope | whence, at last, he draws the substantive, blauson, Clement the Fourth, who died in the year 1628, or blazon. Others, with far greater plausibility, is the first on which a coat of arms is found; nor de luce it from the English, to blaze, which in a are arms to be seen on scals or coins older than the proper sense, signifies 10 flash, to burn with, or tenth or eleventh century. The first French coin cast a great fiame, and in a figurative, and active with arms is a golden denier of King Philip de signification, to set forthi, to publish, to proclaim ; Valois, on which he is represented holding with but the most general, as well as the most rational his left hand a sculcheon semée of fleurs de lis. | opinion is, that both the word blazon, and the This piece of gold, coined in 1966, was called in English, to blaze, comes from the German French ecce, by reason of its bearing the escut Blafen, that is, to sound a horn, or a trumpet; cheon of the arms of France. There are, indeed, because the knights and nobles who came to more antient figures to be seen, either in stand enter the lists at tournaments, caused those instruards, or medals, but neither Princes nor cities, ments to be sounded, to proclaim their arrival ; made use of them, as formal or regular bearings; || whereupon the Heralds sounded also their trumand no author of note mentions the heraldic sci- | pets, and then blazoned the coats of arms of the ence above those ages: to all this may be added, tilters; that is, displayed and described them that it is very probable, this art, like most human aloud, and sometimes expatiated on the praises of inventions, was insensibly introduced and esta. the bearers. Hence, probably, it is that the blished, and that having remained in a rude and word, to blazon, foru:erly signified, to display or unsettled state for many ages, it was at last per set forth a man's ill or good qualities, or to give fected and fixed, by the crusades and tourna a character of him : but now use restrains it to an
ill sense; for by blazoning a man, we only mean As to the name of blazonry, authors differ no to expose him, to display him in his proper less about it than about the origin of the art colours, to speak ill of lim, &c.; but here it is itself; some, by a metathesis, derive it from the to be observed, that some pretend, that in the last Hebrew sobal, which in Latin signifies, tulit, signification, the verb, to blazon, is more antient portavit, “he has borne;" others with greater than the heraldic rules, or blazonry itself; and, to consonance, but as little reason, deduce it from support their opinion, they alledge, that when the Greek BLASTEIN, which in Aristosle signifies the kniglits of the shield received their order, they in Latin, distorquere, and in English, to wrest, were enjoined, not to suffer ladies to be bluzoned; distort, to set awry; and, taken more extensively, that is, slandered or exposed, in their hearing. to extravagate, or rave; because, say they, in antient times, they who were not initiated into
[To be continued.) heraldic mysteries, looked upon most of the
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ON THE RESISTANCE OF AIR AS A MEDIUM.
Medium denotes that space, or region, through which a body passes in its motion towards any point. The air is a resisting medium, and the resistance it opposes to a body moving is proportioned to the surface which that body offers.
If in a room a feather and a guinea be dropped from the hand at the same instant, the guinea will reach the floor immediately, while the feather descends gently, and with an indirect motion, on account of the resistance it meets with from the air contained in the room. Were they dropped from the hand in vacuo, the time
of descent would be the same in both; for when || which smoke, in common with every other body,
When a sonorous body is struck, a tremulous motion is communicated to all its parts, and by their vibration to the air, which carries the impression forward to the ear. Hence three things are necessary to the production of sound,-a sonorous body to give the impression, a medium to convey it, and an ear to receive it.
That a vibratory motion is produced in the parts of a sonorous body when it is struck, may be found by laying the hand on a bell, or a pair of tongs, when either have received a stroke. In both cases a tremulous motion will be felt in the
parts beneath the hand. As long as this vibraThe two mills A and B have each' an equal tion continues, a correspondent motion is pronumber of sails, whose weight, length, and duced in the air, which motion is well illustrated breadth are in each precisely equal. The one by the circles caused in water on throwing any has its sails fixed edge ways, so as to cut the air substance into it; as these circles extend themwith only a thin edge: the other offers the whole selves in every direction, so do the parts of the breadth of its vanes to the air. On giving the air that surround a sonorous body when this sails of both an equal impulse, they will begin last receives a stroke; each part communicates to turn round with equal velocity ; but the one the motion impressed upon it to the portion of which presents the whole surface of its vanes | air next it, and thus are generated a succession soon begins to move slower, and at length stops, l of waves that float the sound to the ear, in whatwhile the other still continues in motion. The | ever direction it may be placed. reason is obvious; this last, offering no greater Sound, whether it be loud or feeble, moves surface to the air than the edge of the sails, finds always with the same velocity by night or by less resistance, and therefore obeys the impulse day, in hot weather or cold, except that its veloit had received for a longer time.
city is a little impeded or accelerated by strong An arrow which offers its point to the air flies | currents of air; but the distance to which sound a considerable way, but an arrow whose side is | is carried depends on the force of the impression opposed to the current of air falls immediately. made on the air. Sound is not instantaneous
If a ball, and a quantity of shot equal to it in but progressive ; it travels at the rate of thirteen weight, be discharged from two guns at the same miles in a minute, or 1142 feet in a second. instant, and with the same velocity, the former | Every body knows that the flash of a gun is seen will be sent to a much greater distance than the before the report is heard, and that lightning latter, for the sum of the surfaces of the shot sometimes precedes the thunder several seconds ; greatly exceed the surface of the ball.
the flash and the report are nevertheless generated Winged animals are incapable of flight in at the same instant; but the former reaches us Facuo; for as they make use of the resistance of with the velocity with which light travels, that the air to facilitate their motions (in the same is, at the rate of 200,000 miles in a second of way as fishes make use of the water by striking time, whereas the latter travels at the rate of only it with their tails), when no such resistance offers, || 1142 feet in the same period. Availing ourtheir wings are useless. If a butterfly be sus || selves of this knowledge, we may at any time pended from the middle of a receiver by a thread ascertain our distance from the seat of a storm, fastened to its horns, it will fly about with ap- | by counting on a stop-watch the number of parent ease so long as the receiver remains filled || seconds that elapse between the flash of lightning with air, but no sooner is the air extracted from and the thunder, Suppose, for example, the it than the butterfly hangs perpendicularly, in- latter be heard five seconds after seeing the capable of raising itself by any efforts that it former, then the report has travelled over five makes.
times 1142 feet, or something more than a mile. Smoke, being a lighter Auid than air, generally || As a stop-watch is not always to be had, the ascends; but in moist and hazy weather it is seen calculation may be made by means of the pulse to fall, for then the air possesses less density, || at the wrist; in every healthy person this comsherefore can make less resistance to the tendency | monly beats about seventy-five times in a minute,
OF THE ECHO.
and in one beat of the pulse of such a person sound passes over the sixth part of a mile, con
Echoes are caused by the reflection of those sequently in six pulsations it will pass over a undulations in the air by which sounds are promile.
pagated. When a pebble is thrown into a pool, Air, though the common conductor of sound, the water which receives its impression recedes is not the only one; water conveys it to the ear on all sides towards the margin, having reached much more strongly. The unassisted human
which it is driven back. The same undulations voice has been heard over water to the distance
are produced in the air by a stroke on a sonorous of ten or twelve miles; a person has been heard body, or by the voice, and when in their retroto read equally as distinctly at the distance of cession from the point of impulse the undulations 140 feet on water as he could be heard on land encounter a rock, a house, or any other similar at the distance of 76 feet. The Romans were surface, they are reflected or driven back, which so well acquainted with the property of water to causes an echo; to hear this echo it is necessary, encrease the force of sound, that they had a however, that the ear be in the line of reflection. canal of water carried under one of their theatres which was too large to admit of the voices of the performers being heard in the remoter parts of the building. It appears from various experiments that, in general, the denser the inedium is, the more intense is the sound; fiannel, how.
P ever, is an excellent conductor of sound; put a narrow slip of it round the middle of a poker, then roll the ends of the flannel round the first fingers of each hand, and put these fingers in the ears; strike the poker against the fender, or any hard substance, and a sound will be produced A.
E which equals in loudness that generated by the largest church bells; at the same time the poker,
Suppose C to be the generating point of sound, if the hand be applied to it, will be found to
or the point where motion is given to the air by make a number of sensible vibrations.
the voice, or a stroke, or any sonorous body, the That wood is a conductor of sound the variety
air will immediately recede in a straight line to. of inusical instruments made of it fully evinces; wards the rock P, which will reflect it back again the slightest scratch with a pin, at one end of a
by the same line, and p:oduce, to a person standlong piece of timber, will be distinctly heard by ing at C, an echo of the original sound. But if an ear applied to the other.
the generating point of sound were at A, the In music, the tone of a sound depends on the undulations would reach the rock by the oblique time that a string vibrates; some strings have line A d, and be reflected by the oblique line long vibrations, and produce deep or grave tones; d E, so that no echo would be heard by an ear hence the different potes which a violin or harp
at A or at C, while a person standing at E would are capable of producing. If a long musical hear one because he is in the line of reflection. string be divided into two equal parts by a bridge,
It sometimes happens that an echo is heard each half will produce a noże eight times higher | by a person whom the direct sound did not reach. than that which issued from the string before; il 1f between A and E there were a hill, this would hence it appears that the vibrations which are
be the case with a person standing at E when inost rapid produce the sharpest sounds.
sound was generated at A; for though the hill A sort of sympathy exists between borlies in
would prevent the undulations in the air reacha state to produce accordant sounds. If strings || ing him in their retrocession from A, and conin unison are placed near each other, both will sequently his hearing the direct sound, yet sound when one is struck; even if the distance when reflected by the rock they would be carried between them be two or three feet the same
to his ear, and he would hear the echo. An thing will occur; when the strings are not in echo, however, supposes that there is a distance unison, no such effect takes place. A wet finger of seventy or eighty feet between the generating pressed round the edge of a drinking-glass, will point of sound and the reflecting surface; if the produce its key; if the glass be struck so as to space be less no echo can be produced. produce its pitch, and an unison to that pitch be There are echoes which reflect the sound sere. strongly excited on à violincello, the glass will ral times; this happens when there are a numbe set in motion, and if near the edge of the ber of walls, rocks, &c. whence the sound is retable, will be liable to be shaken off.
flected from one to another; but for a person to
hear these repeated echoes, he must be so situ vation of the mercury is twenty-eight inches, ated as to intercept the undulacions each time and its greatest thirty-one. they are reflected. At Roseneath, near Glasgow, Since the suspension of the mercury in the there is an echo that repeats three times a tune barometer is occasioned by the pressure of the played with a trumpet. Near Roine there was atmosphere, and since the pressure decreases from one that repeated five times any thing which was the earth upwards, it follows that the column of said. At Brussels there is an echo which an mercury ought to be shorter at the top of a high swers fifteen times. Between Coblentz and Bin mountain than at its base. This is actually the gen there is one which differs from most others; case; in every hundred feet of perpendicular ascent in common echoes the repetition is not heard the mercury sinks about the tenth of an inch, till some time after the words have been uttered, consequently at the height of a thousand feet it in this the person who speaks is scarcely heard, will descend a whole inch; and thus, by taking but the repetition is clear, and surprisingly va a barometer to the top of a mountain, or any ried; the echo in some cases appears to be ap other considerable eminence, we may ascertain prouching, in others receding, and sometimes it its perpendicular elevation. is heard distinctly, at others scarcely at all; one The thermometer is used for marking with person bears but one voice, while another hears precision the changes which take place in the sereral. At a place near Milan, in Italy, the temperature of the atmosphere. Like the baro. sound of a pistol is returned thirty-six times. meter, it consists of a tube closed at the top, or,
The phenomenon of a whisper made against in technical language, hermetically sealed, and the wall on one side of the gallery at St. Paul's fixed to a graduated frame. It is constructed on cathedral, is thus explained :-the wall being this principle, that fluids of every description, extremely smooth is an excellent conductor of and mercury in particular, expand by heat, a'd sound; the undulations made in the air by the are contracted by cold. If a thermoineter be voice are reflected both ways by the wall, and plunged into boiling water it will rise to 212°; meet at the opposite side; to the hearer, there. this is called the boiling point. If it be plunged fore, the effect is the same as if his ear was into melting ice, it will fall to 32°; this is termed close to the mouth of the speaker,
the freezing point. The utmost extent of the
mercurial thermometer, both ways, are the points OP THE BAROMETER AND THERMOMETEK.
at which quicksilver boils and freezes; it boils
at a degree of heat equal to 600°, and freezes The barometer is an instrument in such ge when it is reduced as low as 39° or 400 below 0, neral use that a description of it is unnecessary; consequently the whole extent of the mercurial the upper part of the tube is a vacuum, thus thermometer is 640 degrees. formed:- the tube, which is closed at one end prior to its being fixed to the frame, is com.
of the HYGROMETER, AND THE RAIN-GAUGE. pletely filled with mercury or quicksilver ; every particle of air is, of course, expelled froin it; a
The hygrometer is used for ascertaining the hoger being applied to the open end of the tube,
different degrees of humidity in the atmosphere. to prevent the mercury from running out, it is | The most simple instrument for this purpose, tben inverted and plunged into a cup containing and one sufficiently accurate for common obsermercury; that in the tube then subsides three
vation, may be made by suspending from a wall er four inches, leaving a space above it which is
a weight fastened to a piece of twisted catgut; a perfect vacuum. The tube, and the cup in
in damp weather the catgut will contract, in dry which it is immersed, are then attached to the weather it will extend, and the difference, or va. graduated frame of the barometer; and as there
riation, may be shewn by fixing a scale of equal is no pressure of air on the upper surface of the
parts on the wall near the weight, and a small column of mercury within the tube, the pres index to the calgut. sure of the atinosphere on the surface of that
A piece of spunge makes a very good thermo. contained in the cup forms a counterpoise to
meter, particularly when, after having been freed the included column, and keeps it from running from all impurities by being washed, it is dipped out. When, however, the atmosphere is less into water in which sal ammoniac, or any other dense than usual, the column sinks a little, the salt, has been dissolved; for, when the spunge is air having somewhat less weight; when the at dried, the saline particles imbibe the moisture, mosphere is more dense, the pressure upon the and the sponge will every day vary in weight mercury in the cup being greater, that in the
according to the different degrees of moisture in tube rises. These variations are included within the atmosphere. about three inches, in our climate the least ele The rain gauge shows the height to which rain