Chautauqua Institution

BY PROF. J. T. EDWARDS, D. D.

Director of the Chautauqua School of Experimental Science.

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FIRE.—PHYSICAL PROPERTIES.

Clearness, accuracy, and brevity are the essentials of good definition. That it is no easy task to combine these, every teacher realizes.

Perhaps it is near the truth to say that fire is that operation in nature which at the same time evolves heat and light. The operation is, at the present time, supposed to be a certain vibration of ethereal or more solid substances. All matter is in motion. Whence this motion was first derived no philosopher can tell, unless he goes back to that primal source of both matter and motion, which in the beginning created the heavens and the earth, and said, “Let there be light, and there was light.”

Prof. James Dwight Dana[1] declares that the first act of creative power must have been heralded throughout the universe by a flash of light. Thus the geologist unites with the scriptural narrator, in the statement that light and heat belonged to the first day of creation, although scoffers for a long time ridiculed the idea that light could exist without the sun.

All space is supposed to be filled with a substance called ether, and that it permeates even solid material. When, for any reason, the natural motion of the molecules of matter is much increased, these molecules have the power of imparting their vibration to the ether in contact with them, and that in turn may produce vibrations in other substances, and if these vibrations come in contact with the nerves of touch, there follows the sensation of warmth or heat. If the vibrations of the ether are still more rapid, when they fall upon the retina, we have the sensation of sight, and we call the agent light. Heat and light, then, are the same. In one instance the vibration is capable of affecting one set of nerves, and in the other, two sets of nerves. The heat-vibration can be discovered by the sense of touch alone, but the light-vibration may be detected both by the eye and the touch.

This variation in sensations, when produced by the same cause, may be illustrated as follows: Apply some salt to the tongue, and place some also in a wound, the two sensations are entirely unlike. Again, the vibrations of a body may be so slow that we can discover them by touch, as showing resistance, or so rapid that they are reported to the ear as a shrill sound, or they may be increased so intensely as to evolve heat, and if still more increased in rapidity, affect the eye as light. The spectrum affords us still another illustration of this truth. Pass through a prism a single ray of light, lo, it appears on the screen in all the colors of the rainbow. Nor is this all; between the bright colors, and beyond the violet and the red are invisible lines, and the various parts of the spectrum, although all are produced by the one ray, are capable of creating quite different results. If one should place a delicate thermopile below the red color, it at once reports heat, although the eye sees nothing there. The beautiful colors of the spectrum flash their light into the eye, raise the temperature of the thermometer and affect chemical transformations, while, still more wonderful, the dark lines above the violet, though unseen and not indicated by the thermopile, act upon the sensitized plate of the photographer with decided chemical force. Thus changes in vibrations as to rapidity, length and direction make changes in the resulting sensations.

Light-waves are always heat-waves, and heat-waves may, by increasing the rapidity of the vibrations, become light-waves. It will be observed that three of our senses are close akin. Hearing, feeling (as regards warmth) and seeing are all produced by vibrations. It is quite in accord with the doctrine of modern science to believe that the morning stars did “sing together,” for light is essentially rhythmic, and to senses adapted to the perception of their harmonies, the sunbeams would make music. The various colors of the spectrum differ solely in the wave-lengths of their vibrations. The red corresponds to low pitch in music and the violet to high pitch. As the vibrations of air striking upon the ear increase in rapidity, the sound rises in the scale. There is this difference between the ear and the eye—the former, if trained, can detect all the tones in a chord of music, while the latter, however cultivated, can not discern the varied colors blended in white light.

There must be sixteen vibrations in a second to produce a continuous sound. When these vibrations reach thirty-eight thousand in a second they become inaudible.

Eisenlohr[2] informs us that the red color in the spectrum has four hundred and fifty-eight trillion vibrations in a second, and extreme violet seven hundred and twenty-seven trillions. The former yields 37,640 waves in an inch, and the latter 59,750 waves in the same space. Now mark another beautiful analogy between sound and sight. In looking at the spectrum we can not discern the light or heat below the red color, because the waves are so slow. Ascending the gamut of color, the rapidity of the vibrations increases, until just beyond the violet it becomes so great that the eye can detect no color.

MECHANICAL ENERGY TRANSFORMED INTO ELECTRICITY.

Ex.—The boy on the insulated stool is repeatedly struck with some furry substance, like a tiger skin. He becomes highly electrical and capable of emitting sparks.

The same fact is discovered in the world of sound—beginning with vibrations which are too slow to be heard at all, we ascend the scale eleven octaves, when the vibrations become so rapid as to be inaudible. Complete darkness may be caused by either too slow or too rapid vibrations of light and heat, and utter silence by the same conditions in the sound waves.

SOURCES OF LIGHT AND HEAT.

These are five in number: The sun and stars, chemical action, percussion, friction and electricity. Stars are suns, but at a vast distance from our earth, the nearest being twenty trillions of miles away. To other systems they doubtless perform the offices of suns. Being so remote, however, although of myriad number, their influence upon our earth is hardly appreciable, and will not, therefore, be here considered.

Our sun is an immense reservoir of energy. It is difficult to conceive its size. It would require twelve hundred thousand of our globes to equal it in volume. More than one hundred such worlds as ours might be strung upon the line forming its diameter. The sun has been for ages throwing off its vibrations of heat and light. Thousands of years before fires were kindled on hearthstones this form of energy, according to the modern doctrine of the correlation of forces, was locked up in the tropical vegetation of the coal periods, and in the great deposits of coal preserved for future use. The same anticipatory benevolence which projects on its journey the friendly ray of the north star, forty-three years before the mariner’s eye can see it, provided fuel for man thousands of years before it was needed.

This energy of the sunbeam reappears in the summer warmth of our dwellings in winter, in the expansion of steam, in the blow of the trip hammer, and throbs even in the pulsations of the human heart.

The cells of all plants need the force of the sun’s rays to separate the carbon from the oxygen contained in the carbonic di-oxide absorbed by the rootlets and stomata of the leaves. Thus the great luminary builds the forests and clothes the earth with verdure. “All flesh is grass,” and therefore to the forces of the sun’s vibrations we must trace not a little of animal growth and strength. The sun gives out more heat than it would if six tons of coal were burnt on every square yard of its surface every hour. Sir John Herschel[4] declares that its light is equal to that of one hundred and forty-six calcium lights, each one formed of a ball of lime equal to the sun in bulk; yet even a small calcium light is so dazzling that the eye can not look steadily at it.

The careless expression sometimes heard when the moon shines brightly, “It is as light as day,” is a striking hyperbole, for it would require eight hundred full moons to equal the brightness of daylight.

Of all forms of paganism, that of the Fire Worshipers[5] seems least unreasonable, for the sun is even now, to us, the best symbol of beneficence and unfailing energy. After thousands of years it shows no diminution of power, and although the imagination can conceive the possibility of its destruction, the most accurate scientific observations have not discovered the slightest indications of its lessening influence. “His going forth is from the end of the heaven, and his circuit unto the ends of it; there is nothing hid from the heat thereof.”

CHEMICAL ACTION.

In a preceding article the chemistry of fire has been considered at some length. It only remains to mention briefly a few of the physical phenomena attending it. When elements unite by the force of affinity, it is supposed that their atoms rush together, and that their motion is converted into heat.

In the case of the galvanic battery the impetuous movement of the atoms toward the poles becomes electricity. We have constantly recurring instances in nature of that great truth that energy, though constantly disappearing is never lost, but reappears under new manifestations and a new name. It may for a time remain dormant, and anon become perceptible, as in the case of latent heat. For example, in mixing five pounds of water at a temperature of 212° Fahrenheit, and five pounds of ice, seven hundred and fifteen units of heat disappear in melting the ice, and the aggregate temperature of the mass is proportionally lower than that of the substances united. But upon their returning to their former state, this latent heat reappears as sensible heat.

In chemical action producing fire, the uniting materials are usually converted, first, into a gaseous form, but there are some exceptions. The most interesting is the following: When a few flakes of iodine are placed upon a fragment of phosphorus, the atoms of the two elements rush together with great energy, producing spontaneous combustion, and liberating sufficient heat to burn the superfluous iodine, with the evolution of beautiful violet fumes.

The mechanical action in flame is full of interest. Its brightness always seems to depend upon the incandescence of solid particles. This can easily be seen in an ordinary lamp. A piece of cold porcelain inserted in a flame will cool the incandescent carbon, and it will be deposited as soot.

The Bunsen[6] burner clearly proves that the brilliancy of our lights depends upon the incandescence of the carbon. This is a contrivance for passing jets of air through a flame, so that the intimate mixing of the oxygen of the air with the carbon will cause the immediate combustion of the latter. This results in converting it instantly to invisible gas (CO2) before incandescence, and consequently the Bunsen flame, while it is intensely hot, emits but a feeble light.

Any physical change that facilitates the movement of atoms seems to increase the intensity of chemical action.

An instructive experiment illustrating the characteristics of different kinds of flame may be performed as follows: Place near each other a small alcohol lamp and a piece of paraffine candle; when lighted observe the two flames. The three cones in each can be easily discerned, the candle burns with a much brighter light, showing it to be richer in incandescent carbon. Insert in each flame a piece of fine wire or narrow strip of glass, either of these will be much more quickly heated by the alcohol lamp, because its flame is richer in hydrogen. If a glass jar which is cold be placed over each, a film of vapor (H2O) will gather on that covering the alcohol lamp with greater rapidity than on the other. If the jars remain over the flames until they are extinguished by the lack of oxygen, more carbonic anhydride (CO2) will be formed from the combustion of the alcohol.

PERCUSSION.

When a blow is arrested by an object, the motion is converted into heat. The ancient flint-lock gun and the percussion-cap fire-arm both illustrate this fact. In the former, the descending flint struck out the spark, and in the latter the cap is exploded by the arrested hammer. The stroke of a cannon ball is attended with a flash. If the world were suddenly stopped in its course, heat enough would be generated to set it on fire. Nitro-glycerine and dynamite are exploded by percussion. Familiar illustrations of this scientific truth meet us in everyday life. It has even passed into a proverb with a moral application, that “hard cracks make the sparks fly.” A novel effect of percussion may have been noticed when a fall upon the ice has resulted in a mechanical disturbance of the optic nerve which revealed whole constellations of stars never yet catalogued.

FRICTION.

It is a spirited sight to watch the operation of sharpening tools upon a grindstone or emery wheel run by steam. Showers of sparks are produced by the friction. We often observe the same phenomenon when the brakes are applied to rapidly revolving car wheels. Rails are heated by the friction of the passing train. You may have had the misfortune, while riding, to have one of your carriage wheels become set, caused by the box of the hub, and the axle becoming so heated by friction as to “unite” their surfaces. All machinery requires constant watching and lubrication to prevent undue friction and serious wearing.

Mills have not unfrequently been set on fire by rapidly revolving belts coming in contact with the woodwork. When the whale, frantic with the pain of the harpoon, darts away with lightning speed, the sailors are compelled to dash water over the spinning wheel on which the rope is wound.

In all these instances motion is transformed into heat.

ELECTRICITY.

Galvanic, frictional, magnetic, thermal and animal electricity are all capable of producing heat. The first also produces an intensely brilliant light. We have long been acquainted with the “Voltaic arc”[7] of the galvanic battery, but less familiar are the magnificent manifestations of frictional electricity. Dynamo-electric machines are of comparatively recent construction, and their object is to convert mechanical energy into that of electric currents, and vice versa.

A striking application of galvanic electricity is frequently seen in the discharge of gunpowder and other explosives, by making the electric current pass through a small platinum wire which is in close contact with them.

Electric energy is propagated in waves, and this wire, being so small, is incapable of transmitting them all at once, so they beat upon it until their repeated blows cause it to become red hot, and the material in contact is thus ignited.

Perhaps the grandest illustration of this action was seen in blowing up the rocks of Hell Gate[8] in the East River, and thus opening a safe passage for the commerce of the world. The tiny finger of a little child, the daughter of the engineer, at a given signal, pressed the key that closed the circuit, and, like Æolus,[9] when he struck the rock, set free the mighty elements of destruction.

This same principle, viz.: that resisted motion becomes heat and light, is seen in both the Brush and the Edison electric lights. In the former, electric currents pass along wires to carbon points, shaped like a crayon, and covered by a film of copper, and separated by a distance of about one half inch. The air between is a non-conductor, and here the flame is formed. In the Edison light, however, the two conducting wires enter a glass globe, from which the air is excluded. Here they are connected with a spiral wire about as large as a knitting needle, and three-quarters of an inch in length. When the electricity is turned on, this spiral glows with an intensely brilliant white light.

A marvelous illustration of the relation between electric and sound vibrations is found in the telephone and microphone. The former is becoming a household necessity; the latter, though not so well known, is not less wonderful. It brings to our ear the tick of a watch miles away, and through it the walking of a fly sounds like the tramp of a horse.

DISTRIBUTION OF HEAT.

Heat is distributed by radiation, conduction, and convection. By the first we mean that heated bodies have the power of projecting from themselves, by means of the ether, their own vibrations. Thus the sun is constantly distributing its light and heat in all directions. Conduction takes place where the molecules of a substance nearest a fire first become heated and then impart their motion to the remainder of the mass, somewhat as in a row of suspended ivory balls, the first of which, when struck, transmits its motion from ball to ball, the last one flying off.

Convection takes place in liquids and gases. Here the particles in contact with the heated body becoming lighter by expansion, rise, and are followed by others, thus forming a current.

The process of warming a room illustrates the three methods of heat distribution. The heat passes through the stove by conduction, away from it by radiation, and to the remote parts of the room by convection.

EFFECTS OF HEAT.

They are four in number. Rise of temperature, expansion, liquefaction, evaporation. The first indication of the presence of heat is discovered by an elevation in temperature. Though man is not a reliable thermometer, he would be able, ordinarily, even if blind, to chronicle the progress of the sun, from horizon to horizon, by the increasing and decreasing warmth. The little thermometer placed beneath the tongue of the invalid gives reliable report of the combustion going on within his system. We see a thousand illustrations of the expansive effects of heat, many of which are familiar to all. The exceptions are more interesting than the rule, and less known, the ordinary rule being that heat expands and cold (absence of heat) contracts. Water contracts by cold until it reaches the temperature of 39°, and then expands with great violence until congelation is completed, at 32°. A British officer in Quebec filled a twelve inch shell with water, and closed the fuse hole with a wooden plug securely driven in with a mallet. Upon being exposed to intense cold the plug was projected a distance of several hundred feet, and a long tongue of ice was found protruding from the opening.

It is supposed that sufficient heat would convert all solids first into liquids, and then into gases. In the process of distillation, if we wish to retain its products, we combine both heating and cooling.

The knowledge of the melting and vaporizing point of substances is of immense value. We are enabled thus to drive off and secure the various ingredients entering into many complex substances. A notable instance is seen in the means used to secure the rich and varied products of petroleum.

THERMOMETERS.

These are not the only measurers of heat. We have the pyrometers, used for ascertaining the temperature of extremely hot bodies, and the thermo-electric pile, an apparatus which constitutes the most delicate test for heat which has been devised. It will detect heat in the body of a fly walking near it.

Thermometers are of three kinds, as to the materials used. They are air, alcohol, and mercurial. In each case the contraction and expansion of these respective substances are made to register variations of heat and cold. They are of three kinds, as to their system of grading—RÉaumur’s, the Centigrade, and Fahrenheit’s. The first two make zero the freezing point; the last makes 32°. The boiling point of RÉaumur’s is 80°, the Centigrade 100°, and Fahrenheit’s 212°. Once more changing the basis of classification, we find thermometers divided into three classes, with reference to the purposes they serve. The ordinary thermometer records the degree of heat or cold at the moment of observation. The differential thermometers can be made of two ordinary thermometers, by wrapping a piece of cloth around the bulb of one; these would show at any given moment whether it was growing warmer or colder. If it is growing warm, the column of mercury in the thermometer with the covered bulb will stand lower than the other, as the cloth prevents the heat reaching the quicksilver as readily as in the other. If it is higher than in the other, the weather is growing colder, as the cover prevents the heat from going off as rapidly as from the other. The third class, the registering thermometer, is so called because it marks the extremes of temperature. Without going into detail, it is perhaps sufficient to say that a minute bar of steel is placed on top of the column of mercury, and remains at any point to which it is pushed, thus recording the greatest degree of heat during any given interval of time. Somewhat similar in arrangement is the alcohol thermometer, marking the greatest degree of cold. It will, of course, be understood that almost all apparatus is greatly varied to serve special purposes. The limits of our article will preclude further discussion of fire in relation to light, although the subject of both physical and physiological topics is full of fascination and value.

End of Required Reading for March.

The most important question for the good student and reader is not, amidst this multitude of books which no man can number, how much he shall read. The really important questions are, first, what is the quality of what he does read; and, second, what is his manner of reading it. There is an analogy which is more than accidental between physical and mental assimilation and digestion; and, homely as the illustration may seem, it is the most forcible I can use. Let two sit down to a table spread with food; one possessed of a healthy appetite, and knowing something of the nutritious qualities of the various dishes before him; the other cursed with a pampered and capricious appetite, and knowing nothing of the results of chemical and physiological investigation. One shall make a better meal, and go away stronger and better fed, on a dish of oatmeal, than the other on a dinner that has half emptied his pockets. Shall we study physiological chemistry and know all about what is food for the body, and neglect mental chemistry, and be utterly careless as to what nutriment is contained in the food we give our minds? Who can over-estimate the value of good books, those ships of thought, as Bacon so finely calls them, voyaging through the sea of time, and carrying their precious freight so safely!—Prof. W. P. Atkinson.