1429. Burning glasses had, of course, been employed from the most

primitive times, but one can imagine the despair of an early Briton who had to wait for a sunny day before he could boil his kettle. Incredible as it may seem, it was not a time well within the memory of many people living to-day that matches in anything approaching the form now familiar were offered to the public. The way for their manufacture had been prepared by two discoveries; one by a German who isolated phosphorus in 1669; the other by a Frenchman who produced chlorate of potash in 1786. From this latter date the production of fire was much facilitated, and a few years before Queen Victoria came to the throne, John Walker--a chemist of Stockton-on-Tees--produced the first friction matches of which there is any certain record. These, called “Congreves,” were sold in boxes of fifty for 2/6, and their success soon led others to experiment in match manufacture, so that improvements were rapidly invented and factories sprang up in all parts of the country. It would be a difficult task to compute accurately the value to the human race of the introduction to general use of this little article. At the present writing, in America the consumption of matches amounts to over a billion of matches a day. How Matches Are Made. To-day matches are in such demand that the ingenuity of man has devised a machine which makes complete matches without the help of the human hand. At the very start of operations a man feeds blocks of wood into the jaws of the machine, and thenceforth the mechanical monster does its own work. Seizing the block from the man’s hand, the machine grips it between rollers and forces it against rows of keen-edged cutters, which are so arranged that there is little or no waste. Each of these cutters (and there are usually forty-eight in a machine) severs a piece of wood of exact size and shape. At the same moment a plate rises from beneath, which thrusts these little pieces of wood into a moving flexible cast-iron band, or rather into small holes in this band, from which the embryo matches project like bristles. This traveling band is about 700 feet in length, and follows a serpentine course in its journey, which occupies about an hour from start to finish, the speed being regulated according to temperature so that the matches may be quite dry when they reach the boxes. When the band arrives at the finishing point, a steel bar punches out the matches stuck in its surface and they fall into the inside boxes placed ready to catch them. These boxes are kept continually shaking, to that no spaces are left and the matches fill them completely. As the inside boxes fill, a steel arm presses them forward into their covers, and they are passed along a trough in dozens, quickly wrapped in paper and sealed by a machine. Quick-fingered girls then wrap twelve of these dozen packages and we have the gross packages of boxes so familiar in the stores. It will be seen, that in spite of the marvellous machines which do so much, there is still plenty of work for human hands. How Match Boxes Are Made. The machines for making the wooden box which contain the matches are in themselves wonderful. First, a section of the trunk of an aspen tree, about 30 inches in length, is made to revolve in what is known as a peeling machine. After a few revolutions the rough outer surface is removed, and thin rolls of smooth-surfaced wood are peeled off or veneered. The machine at the same time scores the wood ready for folding by the boxmaking machine. Cut into skillets, i. e., into pieces of the size required for box covers or insides, the ends are next dipped in pink dye to cover the edge of the wood which is not covered by the label. The skillets then go to the box machines, which fold and label them, and after half an hour in a cleverly devised drying chamber they are ready for use. In one room alone sixty machines are labelling and folding the skillets to the number of several thousand gross a day. To see these machines take a strip of wood, push it forward to receive the pasted label, fold it, fasten the joint, wipe off the superfluous paste, and, finally, toss the finished “outside” into a receiving basket, is as fascinating an example of mechanical ingenuity as the industrial world can afford. Are Matches Poisonous? A non-poisonous “strike anywhere” safety match, made from selected, clear, strong cork pine is now made in this country, and is the first satisfactory non-poisonous match. It is also the first match to be endorsed by the country’s recognized leaders and authorities in fire prevention and the conservation of human life and property. The Hughes-Esch Anti-White Phosphorus Match Bill, which became a law during the administration of President Taft, was drafted by the attorneys of the American Association of Labor Legislation, and is the most drastic that our National Constitution will permit. It would be unconstitutional to absolutely prohibit the manufacture of white phosphorus matches, but the Hughes-Esch bill obtains the same result, viz.: absolute prohibition by means of excessive taxation. No match manufacturer in these days of keen competition can afford to pay a tax of ten cents on each box of white phosphorus matches made, and place his factory under government surveillance, for this tax of ten cents is over three times as much as his present selling price to the wholesale trade. As soon as man learned to make fire and light, he began to appreciate how much more comfortable he could be if he could keep his lights burning and to have his light independent of his fire, because it was at times very uncomfortable to sit by a fire on a hot night simply because he wished to use the light which it made. The first schemes devised for lighting purposes merely were the camp-fire torch and the rushlight. With these as a basis, man was enabled to fashion more convenient forms of lighting. He invented the candle and the lamp, and grown “enlightened,” boxed his light in iron and in other metals. Did Candles Come Before Lamps? The candle is in appearance a primitive affair, yet there is little doubt that its predecessor was the lamp. Those old Egyptian tombs, which have unlocked many mysteries, held lamps, and through them evidence of ancient burial customs. Lamps played a part in the solemn feasts of the Egyptians, who on such occasions placed them before their houses, burning them throughout the night. Herodotus, in one of his numerous references to Xerxes, alludes to the hour of lamp-lighting, and evidences abound regarding the use of lamps among the ancient Greeks. Lamps, indeed, are pictured upon some of their oldest vases, indicating the symbolic significance which attached to them. [Illustration: A French watch tower of the fifteenth century in time of siege. The tower is lighted by means of beacons and is protected by dogs. Ruins of such a tower can still be seen at Godesberger on the Rhine.] What Were the Earliest Lamps? It is probable that the earliest lamps were nothing more than convenient vessels, filled with oil and fired by means of rushes. Among the Romans pine splinters, the torch and the flambeau, supplied light until the fifth century before Christ, and even when the Roman began to use the lamp, it was by no means common, finding a place only in the homes of the rich, or on special festival days. The custom of burning funeral lights beside the dead before interment is a very old one. Gregory, interpreting its significance for the Christian, says that departed souls, having walked here as the children of light, now walk with God in the light of the living. The Roman, Pliny, refers to the use of the pith of brittle rushes in making funeral lights and watch-candles, which were probably the ancient prototype of the old rushlight of England. Again, in speaking of flax, Pliny states that the part of the reed that is nearest to the outer skin is called tow, and is good for nothing but to make lamp-matches or candlewicks. What Were the Lamps of the Wise and Foolish Maidens Made Of? When lamps had come into general favor, better attention was given to their form and construction. The first seem to have been made of baked clay, moulded by hand into elongated vessels to contain the oil, and provided at one end with a lip to admit the wick. These are the lamps which artists have pictured in the hands of the wise and foolish virgins, though in the opinion of some scholars they were merely rods of porcelain and iron, covered with cloth and steeped in oil. Another early type, which was less common, presents a simple disc with an aperture in the centre for the oil, and a hole for the wick, at one or both of the sides. Under the Empire, when the light of the lamp had become general, the better ones were made of bronze, ornamented with heads, animals, and other decorations, attached to the handles, while as life in Rome partook more of luxury and extravagance, gold, silver, or Corinthian brass were the materials, the designs being more elaborate and complicated. Many and beautiful examples of these ancient lamps have been unearthed from the ruins of Herculaneum and Pompeii. When Were Street Lamps First Used? Dark must have been the lives of those people who, until comparatively recent times, lived, in the absence of sunlight, by the feeble, uncertain light of the primitive illuminants borne by these lamps. And as for street lighting--that was a luxury but seldom indulged in, and then, not for public benefit, but to enhance the glory of a potentate, or grace the obsequies of some great man. Even Rome, at the height of her luxury and beauty, rarely exhibited more than one or two lanterns in her streets. These were suspended over the baths and places of public resort. Occasionally, however, the streets were illuminated during festivals and other public occasions, while the Forum was sometimes lighted for a midnight exhibition. With these glittering exceptions, and that memorable one when, to satisfy the homicidal impulses of a bad emperor, the bodies of Christians were made living torches, Rome was a city of darkness. [Illustration: THE FIRST STREET LIGHT IN AMERICA The first street light in America. Early in 1795 several large cressets were placed on the corners of Boston’s most frequented street. Pine-knots were placed in these fire baskets by the night watchman.] When Were Candles Introduced? Historical records indicate the prevalent use of candles in the earliest days of Rome, but these candles were of the simplest sort--mere string or rope which had been smeared with pitch or wax. In the early Christian centuries it was the custom to dip rushes in pitch and coat them with wax, a method of candle-making that was long continued, for it was not until the fourteenth century that dipped tallow candles were introduced. In the Middle Ages wax candles provided the usual means of illumination, and these were made, not by common craftsmen, but by monks, or by the servants of the rich. Until the fifteenth century their use was confined to churches, monasteries and the houses of nobles, but the demand for them had become so great that the chandlers of London obtained an act of incorporation. As late as the eighteenth century the candles were made by dipping the wicks into melted wax or tallow, but about this time an ingenious Frenchman conceived the idea of casting them in metal moulds. [Illustration: A part of the “Amende Honorable” of Jacques Coeur before Charles VII of France.] [Illustration: A pagan votive lamp of bronze, now in the museum at Naples.] It is only within a modern period that the state or city has assumed responsibility in the matter of public lighting, which for the most part had been left to the good will and public spirit of citizens. But in England a proclamation was issued to the effect that every individual should place a candle in each of the lower windows of his house, and keep it burning from nightfall until midnight. [Illustration: THE FIRST OIL LANTERN The first “Réverbère”--oil lantern--with a metal reflector, used to light the streets of Paris. It was invented by Bourgeois de Châteaublanc in 1765, and used until the introduction of gas.] Paris was the first city to improve upon this method of street lighting, and in 1658 huge, vase-like contrivances, filled with resin and pitch, were set up in the principal thoroughfares. The improvement proving, as may readily be seen, both dangerous and expensive, the falct, so-called, were replaced by the lantern. This was at first simply a rude frame, covered with horn or leather, within which a candle burned. For more than one hundred years this was the extent of the illumination which the authorities could provide. But of course it was understood that no honest man would venture abroad without his torch or flambeau, and as London, Berlin, Vienna, and all leading cities of Europe, were in like case, the darkness of Paris could be borne. [Illustration: Argand got his first suggestion for his burner--invented in 1780--from this style of alcohol lamp, then in general use throughout France.] But progress had been made, and early in the eighteenth century the Corporation of London entered into contract with a certain individual to set up public lights, giving him permission to exact a sum of six shillings from every householder whose actual rent exceeded ten pounds. In the middle of the same century the Lord Mayor and Common Council applied to Parliament for power to light the streets of London better. From the granting of this permission dates improvement in public lighting. Where Did the Word “Gas” Originate? A Belgium chemist, Van Helmont, coined the word “gas” in the first half of the seventeenth century. The Dutch word “geest,” signifying “ghost,” suggested the term to him, and his superstitious neighbors hounded him into obscurity for talking of ghosts. [Illustration: Hanging lamp from Nushagak in Southern Alaska. It is suspended from the framework of the tent by cords. Oils and fats from northern animals give a clear and steady light, and Eskimo lamps are frequently praised by travelers.] [Illustration: WHAT THE BIG TANK NEAR THE GASWORKS IS FOR SIX MILLION CUBIC FOOT GAS HOLDER. Almost every boy and girl has seen the big tank near the gas works, and most of them have wondered what was in it and what it is for. This big tank is a “holder” in which the gas is stored after it is manufactured. The giant holders are reservoirs from which gas is constantly being taken and the quantity on storage constantly replenished, as the ordinary gas plant never ceases manufacturing its product. There is little or no danger of an interruption of the supply by reason of accident, as gas plants are always equipped with duplicate apparatus for emergencies.] When Illuminating Gas Was Discovered. The first practical demonstration of the value of gas made from coal for lighting was made by a Scotchman--Robert Murdock--who in 1797, after some years of experimenting, fitted up an apparatus in the workshop of Boulton and Watt, in Birmingham, England, which successfully lighted a portion of that establishment. The advantages of this kind of lighting were so apparent that its use was rapidly extended, although in many instances the people were afraid of it. For a time this kind of lighting was confined to street lights. One of the first great structures to be lighted by gas was Westminster Bridge in London, and great crowds gathered to watch the burning jets nightly. It was difficult to remove from the minds of the people the belief that the gas-pipes were filled with fire and the jets were only openings through which the flame in the pipes escaped. People sometimes touched the pipes expecting to find them hot, and when the pipes were put in buildings they made sure that they were placed several feet from the walls lest the fire in them set fire to the buildings. The use of illuminating gas for lighting private houses developed quite slowly because of this fear of the fire in the gas-pipes. This was not entirely unwarranted, however, because at first the plumbers did not know, as they do now, how to prevent leakage of gas from the pipes. The methods of joining the pipes were oftentimes imperfect and, not realizing the dangers which would follow leaks, causing explosions, the workmen were often careless in installing the pipes. The first American house in which gas was used for lighting was the home of David Mellville at Newport, R. I. Baltimore, Maryland, was the first American city to use gas for lighting. It was introduced there in 1817. How Does Gas Get Into the Gas Jet? If you hold a cool drinking glass over a burning gas jet for a moment, a film of moisture will form on the inside of the glass and remain until the tumbler becomes warm, and then disappear. Now, then, you will remember that water is a mixture of oxygen and hydrogen, and that when hydrogen is burned in the air, water is formed. It is also true that whenever water is formed by burning anything, hydrogen is present in it. You see, therefore, that the gas used for lighting purposes must contain hydrogen. Let us now learn something more about what gas is made of. Wet a piece of glass with a little fresh lime water and hold this over the lighted gas jet. In a few moments a change takes place in the water. The water turns somewhat milky. This indicates the presence of carbonic acid gas, and the formation of carbonic acid gas, when burning is going on, means the presence of carbon. From these two experiments we gather that the gas in the jet contains hydrogen and carbon. All kinds of illuminating gas contain these two substances. Sometimes there are small quantities of other substances present, but the value of gas for lighting depends on hydrogen and carbon. We have already learned about hydrogen, but it would be well to re-learn about carbon. Carbon is an element, and an extremely important one, for a large part of the composition of every living thing is carbon. It is found in more compounds than any other element. Almost pure carbon can easily be obtained by heating a piece of wood, in a covered utensil, until it is turned into charcoal. Charcoal, which is black, is composed almost entirely of carbon. It is a very interesting product in all ways; in connection with gas we are particularly interested in the fact that carbon will burn when heated in the air or in oxygen. Charcoal is very much like hard coal, both being formed in practically the same way. Ages of years ago many large forests of trees were buried under a layer of soil and rocks, during changes that occurred in the earth’s surface, and the hot inside earth slowly heated the wood, until almost nothing was left but the carbon. [Illustration: WHERE THE GAS IS TAKEN FROM THE COAL GENERATOR HOUSE AND 175-FT. STACK. In the process of gas making, coal is placed in the generator and heated to an incandescent state, then from the top or bottom steam is admitted and forced through the heated coal, producing a crude water gas which is passed on to the carbureter. In this shell enriching oil is produced, but as the oil and the water gas do not effectually unite, they are passed on to the superheater, where, as its name implies, they are subjected to a high temperature which thoroughly gasifies them into a permanent gas.] [Illustration: AN INTERIOR VIEW OF GENERATOR HOUSE.] * Pictures on Gas Manufacture by courtesy of the Consolidated Gas, Electric Light and Power Co. of Baltimore. [Illustration: ILLUMINATING GAS MUST BE SCRUBBED SHAVING SCRUBBERS. After passing into the scrubbers the gas is cooled, passed into the scrubbers, and by contact with wooden slat trays, made up like screens; a large portion of the tar is removed from the gas, the tar passing off to large receptacles.] Soft coal was formed in much the same manner, but the process was not so completely finished. Mixed with the carbon in soft coal we find quite a good deal of other substances, of which hydrogen forms the principal part. This is what makes soft coal valuable in the making of illuminating gas. When soft coal is heated in a closed receptacle a gas is formed which will burn. To show this we have only to take an ordinary clay pipe, put a little piece of coal in the bowl, close the top with wet clay, and put the bowl part of the pipe in the fire. When it is quite hot, a gas will be found coming out of the stem of the pipe, which will, when lighted, burn. The Story In a Gas Jet. ~HOW ILLUMINATING GAS IS MADE~ Soft coal is heated in large tubes of fire clay called retorts, and the gas that is formed is then collected in a large tank and sent through pipes to our homes after being purified. The part of the coal that is left consists largely of carbon and is what we call coke. While the gas that comes directly from coal will burn if lighted, it is not a desirable gas to burn in our homes, because it contains a number of substances that should be eliminated before it is used for lighting. How the Gas Is Purified. From the clay retorts the gas passes through horizontal pipes containing water. This cools it and takes out of it most of the tar and water vapor that are driven off with the gas when formed. These substances settle in the water. The gas then goes through a series of curved pipes, which are air cooled. These pipes constitute what is known as an atmospheric condenser. From these the gas goes into a series of receptacles containing wooden slat trays, made up like screens. These receptacles are called the scrubbers, and they take out of the gas the last traces of tar and some of the other compounds found present. The removal of the sulphur is very important, for burning sulphur gives off a gas which is not only extremely impure to breathe, but also injurious to the health. From the scrubbers the gas goes on through pipes to the purifiers--boxes which contain wood shavings coated with iron rust upon which the sulphur is deposited by chemical action. At the same time the lime absorbs a small quantity of carbonic acid gas, which is formed with the other gases. From the purifiers the gas passes into the great iron tanks, in which it is stored until needed. The gas in the tanks consists chiefly of hydrogen, a number of compounds of hydrogen and carbon, and a small amount of a compound of carbon and oxygen containing less oxygen than carbonic acid gas, known as carbon monoxide. The hydrogen and carbon monoxide burn with a very pale flame, which gives but little light and much heat. The light-giving quality of the gas is found in the compounds of carbon and hydrogen. When these burn, the particles of carbon are heated white hot and glow very brightly, making a luminous flame. There are, of course, some impurities in the purified gas. These are compounds containing sulphur and ammonia. The quantities of these substances, however, are so small that they are harmless; but the compounds taken out in the process of purifying the gas are saved, as considerable use is made of them. The water used for washing the gas is heavily charged with ammonia and is, in fact, the chief source of the ammonia sold by druggists. [Illustration: HOW THE IMPURITIES ARE TAKEN FROM THE GAS PURIFYING BOXES. The principal impurity to be removed is sulphur, and this is accomplished by passing the gas through large iron rectangular boxes filled with wood shavings coated with iron rust upon which the sulphur is deposited by chemical action.] [Illustration: STATION METER HOUSE, SHOWING CONSTRUCTION OF TWO NEW 13-FT. METERS.] [Illustration: HOW THE METER MEASURES THE GAS Fig 1 Fig 3 Fig. 2. Fig 4 Gas first enters inlet pipe _A_ (Fig. 3) passing along _A1_ into covered valve chamber _B_ up through orifice _O_. It then passes down through two of the valve ports at the same time, ports _C_ and _D1_ (Fig. 2). Before _C1_ (Fig. 3) has gotten to its extreme opening, the valve on the opposite side has moved to allow gas to pass down port _D_. On every quarter turn of tangent _P_, one port is opening to receive gas which passes down through the valve ports into the chambers below (see arrows on Fig. 2), which shows the gas passing into chamber _F_. The pressure being greater on the outside of the diaphragm, forces the diaphragm inward and expels the gas from the inside of _D2_ through _D_ and passes over the cross-bar into the fork channel (see Fig. 1). On the other side gas is passing down through port _D1_ (Fig. 2) entering diaphragm _D3_, the pressure being greater on the inside of _D3_ therefore forces the diaphragm outward and expels the gas from the outside of diaphragm _D3_; out through port _C1_ into fork channel same as shown in (Fig. 1). All exhaust gas from the chambers below is checked from entering the chamber _B_ by the slide valve _G_ and _G1_ (Fig. 2). Instead of passing into chamber _B_ it passes over the cross-bars between _D1E1_ and _C1E1_ into the fork channels, then to outlet pipe _N_ (Fig. 3) to house pipe. NOTE: All gas registered must pass through outlet _N_.] In addition to coal gas made in the way just described, there is another form of illuminating gas, in the manufacture of which coal is indirectly employed. This gas, known as water gas, because it is formed by the decomposition of water, is produced by passing steam over red hot carbon, in the form of hard coal or coke. When this is done, the hydrogen in the steam is set free and the oxygen combines chemically with the carbon, to form the carbon monoxide, that was mentioned as being present, in small proportions, in ordinary coal gas. This carbon monoxide is poisonous, if much of it is breathed, and as it has no odor it is difficult to detect when escaping. A number of deaths have resulted from water gas for this reason, and in some states the laws forbid its use for lighting purposes. When water gas is used it must be enriched with some other substances before it will yield much light. You have already learned that neither hydrogen nor carbon monoxide burns with a bright flame, and you will see that water gas must have something added to it to fit it for lighting purposes. The substance usually added is the vapor of some light, volatile oil, like gasoline. This vapor is composed of compounds of carbon and hydrogen, and when it is mixed with the water gas it forms a gas that yields a very satisfactory light; and that may be produced more cheaply than common coal gas. There remains one more form of illuminating gas which has been the subject of much discussion in recent years, namely, acetylene. This is a compound of carbon and hydrogen, in which there is twelve times as much carbon as hydrogen. It has not been discovered recently, for it was known early in the nineteenth century, but its possible use for lighting purposes was not considered then. Attention was directed to it a few years ago by the discovery of a substance called calcium carbide. This is a compound of carbon and the metal calcium, formed by heating to a very high temperature a mixture of coal and lime. It has the peculiar property of decomposing, when treated with water. The calcium present combines with the oxygen and half the hydrogen of the water, to form common slacked lime or calcium hydrate, while the carbon and the remainder of the hydrogen combine to form acetylene gas. The gas formed in this way needs no purifications before burning; it can be produced in small generators, and the production can be checked at any time. When burned in the proper form of burner it yields the brightest of all gas flames. For these reasons it is adapted for use in small villages and for lighting single houses. It is also frequently used in magic lanterns, where a strong and steady light is necessary. But the cost of producing acetylene in large quantities is greater than that of coal gas, and it seems extremely unlikely that it will ever be much used for lighting large cities and towns. How the Light Gets Into the Electric Light Bulb. The incandescent lamp was invented in 1879 and the patents were granted to Thomas A. Edison. There were, however, a number of electrical men who were working on the idea at this time who deserve a great deal of credit for developing the lamp. The incandescent lamp, which is used chiefly for house lighting, consists of a glass bulb from which the air has been exhausted by pumps and chemical processes--in which there is a thin filament of tungsten metal wound on what is called an arbor (as shown in Fig. 4). This filament opposes high resistance to the passage of the current of electricity, and, consequently, is heated to incandescence when a current passes through it. The removal of the air from the bulb prevents the tungsten metal from burning up, as it would do if oxygen were present. The filaments of the first lamps were made of vegetable fibre. The next development was the cellulose process, which is still used in carbon and metallized lamps, although a number of processes are used now which improve the filament considerably. The discovery that tungsten metal could be used in incandescent lamps was made in 1906. The first tungsten lamp manufactured in America was made in 1907. [Illustration: THE DEVELOPMENT OF INCANDESCENT LAMPS Edison’s first lamp with a filament of bamboo fibre.] [Illustration: The carbon lamp--the oldest form of incandescent lamp.] [Illustration: Standard Mazda lamp--the highest development of the incandescent lamp.] [Illustration: The Tantalum lamp developed just before the Mazda lamp.] [Illustration: Improved Mazda lamp for lighting large areas--the most efficient lamp ever made.] The filaments of the first tungsten lamps were composed of two or three short pieces of wire. In 1910, however, a lamp with a continuous tungsten filament was invented which increased the strength of the lamp wonderfully. Mazda is a trade name given to all metal filament lamps made by the prominent American lamp manufacturers. The reason that the Mazda lamp is so much more efficient than the carbon filament lamp is because the tungsten filament can be burned at a much higher temperature than the present carbon filament, without seriously blackening the bulb. How Does an Arc Light Burn? In the arc light a current of electricity is made to leap across from the tip of one rod of carbon to the tip of another that is held a short distance from the first. In passing across the current does not follow a straight path, but makes a curve, or arc, whence comes the name “arc light.” In this form of light the carbons are not enclosed in a space from which air is excluded, consequently there is some destruction of the carbon. The light is due to the fact that the air between the tips of the carbon rods opposes a high degree of resistance to the current, so that the rods become intensely hot at their tips. The high degree of heat causes a slow burning of the carbon at the tips, and the small particles that burn are heated white hot before they are consumed, thus producing light. In order to keep the light from an arc light uniform in strength, it is necessary to keep the tips of the carbon rods always the same distance apart. This is practically impossible, and, as a result, the arc light does not produce light that is well adapted for reading or for other purposes that require constant use of the eyes. The light produced by the arc light is very powerful, however, and for that reason it is much used for street lighting. What Are X-Rays? It was discovered by Professor Conrad Roentgen in 1895, that if a current of electricity be passed through a certain form of glass bulb, from which most of the air has been exhausted, a disturbance is produced in the ether that bears some resemblance to light waves. For want of a better name to give to a disturbance which was not well understood, Roentgen called his discovery the X-Ray, but it is now frequently called in his honor the Roentgen ray. The nature of this disturbance is not yet known, but as it does not affect the eye it is not light. These rays are produced with a glass vacuum tube and a battery from which a current of electricity is sent through the tube. The wires of the battery are connected with two electrodes, one of which consists of a concave disk of aluminum, and the latter of a flat disk of platinum. The X-rays are discharged in straight lines as shown in the figure. The most striking properties of the X-ray is its power to penetrate many substances that are impermeable to light. All vegetable substances, and the flesh of animals, are penetrated by it very readily. Glass, metals, bones, and mineral substances generally are opaque to it. Consequently, when a limb, or even the body of an animal, is exposed to X-rays they pass through the fleshy parts, but are stopped by the bones. Certain substances have the property of glowing, or becoming fluorescent, when exposed to the X-ray, and when screens of paper are coated with these substances they form a convenient means of detecting the presence of X-rays. By holding the hand between a tube that is giving off X-rays and a screen of this kind, the bones of the hand will be outlined in shadow on the screen, and the rest of the surface will glow with a greenish light. If a bullet or other piece of metal has become imbedded in the body, it may easily be located, if it is not in a bone, and the extent of an injury to a bone or a joint may be plainly shown. For this reason the X-ray is now widely used by surgeons. How Man Learned to Fight Fire. When you see the modern fire engine racing through the streets, gongs ringing, with the firemen hanging on and the police clearing the track, you should remember that it has taken man a long time to learn as much as he has about fighting fire. No sooner did man learn to make fire than he found it necessary to learn how to put it out. The first fire apparatus of record is found in Rome. The Gauls burned the city in 390 B. C., each citizen was ordered to keep in his house a “machine for extinguishing fire.” This consisted of a syringe. The first record of an actual machine for putting out fire is by Hero of Alexandria. This contrivance, a “siphon used in conflagrations,” was used in Egypt about a hundred and fifty years before Christ. The first record of what we would call a fire department is also found in Rome. A disastrous fire, occurring in the reign of Augustus called his attention to the benefit of a regular fire brigade would bring. So he organized a fire department. It consisted of seven companies of a thousand men each. The first real fire engines were used in 1633 at a big fire on London Bridge. The first fire hose was invented by the two Van der Heydes in