Science Curiosities E-Book

John Timbs

• Herausgeber: Books on Demand
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Deutsch
• Veröffentlichungsjahr: 2019

Seitenzahl: 491

Beschreibung

Humboldt, in his Cosmos, gives the following beautiful illustrative proofs of this phenomenon: If, for a moment, we imagine the acuteness of our senses preternaturally heightened to the extreme limits of telescopic vision, and bring together events separated by wide intervals of time, the apparent repose which reigns in space will suddenly vanish; countless stars will be seen moving in groups in various directions; nebulae wandering, condensing, and dissolving like cosmical clouds; the milky way breaking up in parts, and its veil rent asunder. In every point of the celestial vault we shall recognise the dominion of progressive movement, as on the surface of the earth where vegetation is constantly putting forth its leaves and buds, and unfolding its blossom. The celebrated Spanish botanist, Cavanilles, first conceived the possibility of "seeing grass grow," by placing the horizontal micrometer wire of a telescope, with a high magnifying power, at one time on the point of a bamboo shoot, and at another on the rapidly unfolding flowering stem of an American aloe; precisely as the astronomer places the cross of wires on a culminating star. Throughout the whole life of physical nature-in the organic as in the sidereal world-existence, preservation, production, and development, are alike associated with motion as their essential condition.

Leseprobe

Science Curiosities

Science CuriositiesPhysical Phenomena.Sound and Light.Astronomy.Geology and Paleontology.Meteorological Phenomena.Phenomena of Heat.Magnetism and Electricity.The Electric Telegraph.Miscellanea.FOOTNOTES:Impressum

Science Curiosities

John Timbs

Physical Phenomena.

Sound and Light.

SOUNDING SAND. Mr. Hugh Miller, the geologist, when in the island of Eigg, in the Hebrides, observed that a musical sound was produced when he walked over the white dry sand of the beach. At each step the sand was driven from his footprint, and the noise was simultaneous with the scattering of the sand; the cause being either the accumulated vibrations of the air when struck by the driven sand, or the accumulated sounds occasioned by the mutual impact of the particles of sand against each other. If a musket-ball passing through the air emits a whistling note, each individual particle of sand must do the same, however faint be the note which it yields; and the accumulation of these infinitesimal vibrations must constitute an audible sound, varying with the number and velocity of the moving particles. In like manner, if two plates of silex or quartz, which are but crystals of sand, give out a musical sound when mutually struck, the impact or collision of two minute crystals or particles of sand must do the same, in however inferior a degree; and the union of all these sounds, though singly imperceptible, may constitute the musical notes of “the Mountain of the Bell” in Arabia Petræa, or the lesser sounds of the trodden sea-beach of Eigg.—North-British Review, No. 5. INTENSITY OF SOUND IN RAREFIED AIR. The experiences during ascents of the highest mountains are contradictory. Saussure describes the sounds on the top of Mont Blanc as remarkably weak: a pistol-shot made no more noise than an ordinary Chinese cracker, and the popping of a bottle of champagne was scarcely audible. Yet Martius, in the same situation, was able to distinguish the voices of the guides at a distance of 1340 feet, and to hear the tapping of a lead pencil upon a metallic surface at a distance of from 75 to 100 feet.MM Wertheim and Breguet have propagated sound over the wire of an electric telegraph at the rate of 11,454 feet per second. DISTANCE AT WHICH THE HUMAN VOICE MAY BE HEARD. Experience shows that the human voice, under favourable circumstances, is capable of filling a larger space than was ever probably enclosed within the walls of a single room. Lieutenant Foster, on Parry’s third Arctic expedition, found that he could converse with a man across the harbour of Port Bowen, a distance of 6696 feet, or about one mile and a quarter. Dr. Young records that at Gibraltar the human voice has been heard at a distance of ten miles. If sound be prevented from spreading and losing itself in the air, either by a pipe or an extensive flat surface, as a wall or still water, it may be conveyed to a great distance. Biot heard a flute clearly through a tube of cast-iron (the water-pipes of Paris) 3120 feet long: the lowest whisper was distinctly heard; indeed, the only way not to be heard was not to speak at all. THE ROAR OF NIAGARA. The very nature of the sound of running water pronounces its origin to be the bursting of bubbles: the impact of water against water is a comparatively subordinate cause, and could never of itself occasion the murmur of a brook; whereas, in streams which Dr. Tyndall has examined, he, in all cases where a ripple was heard, discovered bubbles caused by the broken column of water. Now, were Niagara continuous, and without lateral vibration, it would be as silent as a cataract of ice. In all probability, it has its “contracted sections,” after passing which it is broken into detached masses, which, plunging successively upon the air-bladders formed by their precursors, suddenly liberate their contents, and thus createthe thunder of the waterfall. FIGURES PRODUCED BY SOUND. Stretch a sheet of wet paper over the mouth of a glass tumbler which has a footstalk, and glue or paste the paper at the edges. When the paper is dry, strew dry sand thinly upon its surface. Place the tumbler on a table, and hold immediately above it, and parallel to the paper, a plate of glass, which you also strew with sand, having previously rubbed the edges smooth with emery powder. Draw a violin-bow along any part of the edges; and as the sand upon the glass is made to vibrate, it will form various figures, which will be accurately imitated by the sand upon the paper; or if a violin or flute be played within a few inches of the paper, they will cause the sand upon its surface to form regular lines and figures. THE TUNING-FORK A FLUTE-PLAYER. Take a common tuning-fork, and on one of its branches fasten with sealing-wax a circular piece of card of the size of a small wafer, or sufficient nearly to cover the aperture of a pipe, as the sliding of the upper end of a flute with the mouth stopped: it may be tuned in unison with the loaded tuning-fork by means of the movable stopper or card, or the fork may be loaded till the unison is perfect. Then set the fork in vibration by a blow on the unloaded branch, and hold the card closely over the mouth of the pipe, as in the engraving, when a note of surprising clearness and strength will be heard. Indeed a flute may be made to “speak” perfectly well, by holding close to the opening a vibrating tuning-fork, while the fingering proper to the note of the fork is at the same time performed. THEORY OF THE JEW’S HARP. If you cause the tongue of this little instrument to vibrate, it will produce a very low sound; but if you place it before a cavity (as the mouth) containing a column of air, which vibrates much faster, but in the proportion of any simple multiple, it will then produce other higher sounds, dependent upon the reciprocation of that portion of the air. Now the bulk of air in the mouth can be altered in its form, size, and other circumstances, so as to produce by reciprocation many different sounds; and these are the sounds belonging to the Jew’s Harp.A proof of this fact has been given by Mr. Eulenstein, who fitted into a long metallic tube a piston, which being moved, could be made to lengthen or shorten the efficient column of air within at pleasure. A Jew’s Harp was then so fixed that it could be made to vibrate before the mouth of the tube, and it was found that the column of air produced a series of sounds, according as it was lengthened or shortened; a sound being produced whenever the length of the column was such that its vibrations were a multiple of those of the Jew’s Harp. SOLAR AND ARTIFICIAL LIGHT COMPARED. The most intensely ignited solid (produced by the flame of Lieutenant Drummond’s oxy-hydrogen lamp directed against a surface of chalk) appears only as black spots on the disc of the sun, when held between it and the eye; or in other words, Drummond’s light is to the light of the sun’s disc as 1 to 146. Hence we are doubly struck by the felicity with which Galileo, as early as 1612, by a series of conclusions on the smallness of the distance from the sun at which the disc of Venus was no longer visible to the naked eye, arrived at the result that the blackest nucleus of the sun’s spots was more luminous than the brightest portions of the full moon. (See “The Sun’s Light compared with Terrestrial Lights,” inThings not generally Known, pp. 4, 5.) SOURCE OF LIGHT. Mr. Robert Hunt, in a lecture delivered by him at the Russell Institution, “On the Physics of a Sunbeam,” mentions some experiments by Lord Brougham on the sunbeam, in which, by placing the edge of a sharp knife just within the limit of the light, the ray was inflected from its previous direction, and coloured red; and when another knife was placed on the opposite side, it was deflected, and the colour was blue. These experiments (says Mr. Hunt) seem to confirm Sir Isaac Newton’s theory, that light is a fluid emitted from the sun. THE UNDULATORY SCALE OF LIGHT. The white light of the sun is well known to be composed of several coloured rays; or rather, according to the theory of undulations, when the rate at which a ray vibrates is altered, a different sensation is produced upon the optic nerve. The analytical examination of this question shows that to produce a red colour the ray of light must give 37,640 undulations in an inch, and 458,000,000,000,000 in a second. Yellow light requires 44,000 undulations in an inch, and 535,000,000,000,000 in a second; whilst the effect of blue results from 51,110 undulations within an inch, and 622,000,000,000,000 of waves in a second of time.—Hunt’s Poetry of Science. VISIBILITY OF OBJECTS. In terrestrial objects, the form, no less than the modes of illumination, determines the magnitude of the smallest angle of vision for the naked eye. Adams very correctly observed that a long and slender staff can be seen at a much greater distance than a square whose sides are equal to the diameter of the staff. A stripe may be distinguished at a greater distance than a spot, even when both are of the same diameter.Theminimumoptical visual angle at which terrestrial objects can be recognised by the naked eye has been gradually estimated lower and lower, from the time when Robert Hooke fixed it exactly at a full minute, and Tobias Meyer required 34″ to perceive a black speck on white paper, to the period of Leuwenhoeck’s experiments with spiders’ threads, which are visible to ordinary sight at an angle of 4″·7. In Hueck’s most accurate experiments on the problem of the movement of the crystalline lens, white lines on a black ground were seen at an angle of 1″·2; a spider’s thread at 0″·6; and a fine glistening wire at scarcely 0″·2.Humboldt, when at Chillo, near Quito, where the crests of the volcano of Pichincha lay at a horizontal distance of 90,000 feet, was much struck by the circumstance that the Indians standing near distinguished the figure of Bonpland (then on an expedition to the volcano), as a white point moving on the black basaltic sides of the rock, sooner than Humboldt could discover him with a telescope. Bonpland was enveloped in a white cotton poncho: assuming the breadth across the shoulders to vary from three to five feet, according as the mantle clung to the figure or fluttered in the breeze, and judging from the known distance, the angle at which the moving object could be distinctly seen varied from 7″ to 12″. White objects on a black ground are, according to Hueck, distinguished at a greater distance than black objects on a white ground.Gauss’s heliotrope light has been seen with the naked eye reflected from the Brocken on Hobenhagen at a distance of about 227,000 feet, or more than 42 miles; being frequently visible at points in which the apparent breadth of a three-inch mirror was only 0″·43. THE SMALLEST BRIGHT BODIES. Ehrenberg has found from experiments on the dust of diamonds, that a diamond superficies of 1/100th of a line in diameter presents a much more vivid light to the naked eye than one of quicksilver of the same diameter. On pressing small globules of quicksilver on a glass micrometer, he easily obtained smaller globules of the 1/100th to the 1/2000th of a line in diameter. In the sunshine he could only discern the reflection of light, and the existence of such globules as were 1/300th of a line in diameter, with the naked eye. Smaller ones did not affect his eye; but he remarked that the actual bright part of the globule did not amount to more than 1/900th of a line in diameter. Spider threads of 1/2000th in diameter were still discernible from their lustre. Ehrenberg concludes that there are in organic bodies magnitudes capable of direct proof which are in diameter 1/100000 of a line; and others, that can be indirectly proved, which may be less than a six-millionth part of a Parisian line in diameter. VELOCITY OF LIGHT. It is scarcely possible so to strain the imagination as to conceive the Velocity with which Light travels. “What mere assertion will make any man believe,” asks Sir John Herschel, “that in one second of time, in one beat of the pendulum of a clock, a ray of light travels over 192,000 miles; and would therefore perform the tour of the world in about the same time that it requires to wink with our eyelids, and in much less time than a swift runner occupies in taking a single stride?” Were a cannon-ball shot directly towards the sun, and were it to maintain its full speed, it would be twenty years in reaching it; and yet light travels through this space in seven or eight minutes.The result given in theAnnuairefor 1842 for the velocity of light in a second is 77,000 leagues, which corresponds to 215,834 miles; while that obtained at the Pulkowa Observatory is 189,746 miles. William Richardson gives as the result of the passage of light from the sun to the earth 8´ 19″·28, from which we obtain a velocity of 215,392 miles in a second.—Memoirs of the Astronomical Society, vol. iv.In other words, light travels a distance equal to eight times the circumference of the earth between two beats of a clock. This is a prodigious velocity; but the measure of it is very certain.—Professor Airy.The navigator who has measured the earth’s circuit by his hourly progress, or the astronomer who has paced a degree of the meridian, can alone form a clear idea of velocity, when we tell him that light moves through a space equal to the circumference of the earth inthe eighth part of a second—in the twinkling of an eye.Could an observer, placed in the centre of the earth, see this moving light, as it describes the earth’s circumference, it would appear a luminous ring; that is, the impression of the light at the commencement of its journey would continue on the retina till the light had completed its circuit. Nay, since the impression of light continues longer than thefourthpart of a second,twoluminous rings would be seen, provided the light madetworounds of the earth, and in paths not coincident. APPARATUS FOR THE MEASUREMENT OF LIGHT. Humboldt enumerates the following different methods adopted for the Measurement of Light: a comparison of the shadows of artificial lights, differing in numbers and distance; diaphragms; plane-glasses of different thickness and colour; artificial stars formed by reflection on glass spheres; the juxtaposition of two seven-feet telescopes, separated by a distance which the observer could pass in about a second; reflecting instruments in which two stars can be simultaneously seen and compared, when the telescope has been so adjusted that the star gives two images of like intensity; an apparatus having (in front of the object-glass) a mirror and diaphragms, whose rotation is measured on a ring; telescopes with divided object-glasses, on either half of which the stellar light is received through a prism; astrometers, in which a prism reflects the image of the moon or Jupiter, and concentrates it through a lens at different distances into a star more or less bright.—Cosmos, vol. iii. HOW FIZEAU MEASURED THE VELOCITY OF LIGHT. This distinguished physicist has submitted the Velocity of Light to terrestrial measurement by means of an ingeniously constructed apparatus, in which artificial light (resembling stellar light), generated from oxygen and hydrogen, is made to pass back, by means of a mirror, over a distance of 28,321 feet to the same point from which it emanated. A disc, having 720 teeth, which made 12·6 rotations in a second, alternately obscured the ray of light and allowed it to be seen between the teeth on the margin. It was supposed, from the marking of a counter, that the artificial light traversed 56,642 feet, or the distance to and from the stations, in 1/1800th part of a second, whence we obtain a velocity of 191,460 miles in a second.12This result approximates most closely to Delambre’s (which was 189,173 miles), as obtained from Jupiter’s satellites.The invention of the rotating mirror is due to Wheatstone, who made an experiment with it to determine the velocity of the propagation of the discharge of a Leyden battery. The most striking application of the idea was made by Fizeau and Foucault, in 1853, in carrying out a proposition made by Arago, soon after the invention of the mirror: we have here determined in a distance of twelve feet no less than the velocity with which light is propagated, which is known to be nearly 200,000 miles a second; the distance mentioned corresponds therefore to the 77-millionth part of a second. The object of these measurements was to compare the velocity of light in air with its velocity in water; which, when the length is greater, is not sufficiently transparent. The most complete optical and mechanical aids are here necessary: the mirror of Foucault made from 600 to 800 revolutions in a second, while that of Fizeau performed 1200 to 1500 in the same time.—Prof. Helmholtz on the Methods of Measuring very small Portions of Time. WHAT IS DONE BY POLARISATION OF LIGHT. Malus, in 1808, was led by a casual observation of the light of the setting sun, reflected from the windows of the Palais de Luxembourg, at Paris, to investigate more thoroughly the phenomena of double refraction, of ordinary and of chromatic polarisation, of interference and of diffraction of light. Among his results may be reckoned the means of distinguishing between direct and reflected light; the power of penetrating, as it were, into the constitution of the body of the sun and of its luminous envelopes; of measuring the pressure of atmospheric strata, and even the smallest amount of water they contain; of ascertaining the depths of the ocean and its rocks by means of a tourmaline plate; and in accordance with Newton’s prediction, of comparing the chemical composition of several substances with their optical effects.Arago, in a letter to Humboldt, states that by the aid of his polariscope, he discovered, before 1820, that the light of all terrestrial objects in a state of incandescence, whether they be solid or liquid, is natural, so long as it emanates from the object in perpendicular rays. On the other hand, if such light emanate at an acute angle, it presents manifest proofs of polarisation. This led M. Arago to the remarkable conclusion, that light is not generated on the surface of bodies only, but that some portion is actually engendered within the substance itself, even in the case of platinum.A ray of light which reaches our eyes after traversing many millions of miles, from, the remotest regions of heaven, announces, as it were of itself, in the polariscope, whether it is reflected or refracted, whether it emanates from a solid or fluid or gaseous body; it announces even the degree of its intensity.—Humboldt’s Cosmos, vols. i. and ii. MINUTENESS OF LIGHT. There is something wonderful, says Arago, in the experiments which have led natural philosophers legitimately to talk of the different sides of a ray of light; and to show that millions and millions of these rays can simultaneously pass through the eye of a needle without interfering with each other! THE IMPORTANCE OF LIGHT. Light affects the respiration of animals just as it affects the respiration of plants. This is novel doctrine, but it is demonstrable. In the day-time we expire more carbonic acid than during the night; a fact known to physiologists, who explain it as the effect of sleep: but the difference is mainly owing to the presence or absence of sunlight; for sleep, as sleep,increases, instead of diminishing, the amount of carbonic acid expired, and a man sleeping will expire more carbonic acid than if he lies quietly awake under the same conditions of light and temperature; so that if less is expired during the night than during the day, the reason cannot be sleep, but the absence of light. Now we understand why men are sickly and stunted who live in narrow streets, alleys, and cellars, compared with those who, under similar conditions of poverty and dirt, live in the sunlight.—Blackwood’s Edinburgh Magazine, 1858.The influence of light on the colours of organised creation is well shown in the sea. Near the shores we find seaweeds of the most beautiful hues, particularly on the rocks which are left dry by the tides; and the rich tints of the actiniæ which inhabit shallow water must often have been observed. The fishes which swim near the surface are also distinguished by the variety of their colours, whereas those which live at greater depths are gray, brown, or black. It has been found that after a certain depth, where the quantity of light is so reduced that a mere twilight prevails, the inhabitants of the ocean become nearly colourless.—Hunt’s Poetry of Science. ACTION OF LIGHT ON MUSCULAR FIBRES.