CHAPTER XXXIII.
Liquid Air.

Until quite recently the physicist divided gaseous matter into condensable vapors and permanent vapors. To-day it is known that there are no permanent gases, since all the so-called permanent gases, even to the most tenuous, such as hydrogen, may be made to assume the liquid and even the solid form. The average individual knows very little about hydrogen, but he is very well acquainted with air, and when he was told that the air that he breathes—the gentle zephyr that blows—the wind that storms from the north, or twists itself into the rage of a cyclone in Kansas—may be bound down in liquid form, and imprisoned within the limits of an open tumbler, or be bottled up in a flask or even frozen solid, he was at first impressed with the suspicion of a fairy story. Seeing is believing, however, to him, and the striking experiments from the lecture platform, the approval of the scientists, and the sensational accounts of it in the press, have not only been convincing, but have completely turned his head and made him a too willing victim of the speculator. Liquid air is a real achievement, however, and while it is astonishing to the layman, the physicist looks upon it in the most matter-of-fact way, for it is only a fulfilment of the simplest of nature’s laws, and entirely consonant with what he has been led to expect for many years.

The liquefaction of gases has engaged the attention of the scientist almost from the beginning of the century. In 1805-6 Northmore liquefied chlorine gas. This was done again in 1823 by Faraday. In 1824 Bussy condensed sulphurous acid vapors to liquid form. In 1834 Thilorier made extensive experiments and demonstrations in the liquefaction of carbonic acid gas. In 1843 Aime experimented with the liquefaction of gases by sinking them in suitable vessels to great depths in the ocean. Natterer, in 1844, greatly advanced the study of this subject by both novel methods and apparatus. Liquefaction of air was attempted as early as 1823 by Perkins, and again in 1828 by Colladon, but it was not accomplished until 1877. In this year the liquefaction of oxygen, by Pictet, of Geneva, and Cailletet, of Chatillon-sur-Seine, was independently accomplished. Pictet used a pressure of 320 atmospheres and a temperature of -140°, obtained by the evaporation of liquid sulphurous acid and liquid carbonic acid. Cailletet used a pressure of 300 atmospheres and a temperature of -29°, which latter was obtained by the evaporation of liquid sulphurous acid. In 1883 Dewar, Wroblewski and Olszewski commenced operations in this field, and greatly advanced the study of this subject. In January of 1884, Wroblewski confirmed the liquefaction of hydrogen, which had been imperfectly accomplished by Cailletet before. In the liquefaction of oxygen and nitrogen, the principal component gases of air, the liquefaction of air itself followed immediately as a matter of course.

Air has usually been held to consist of four volumes of nitrogen and one volume of oxygen, with a very small proportion of carbonic acid gas and ammonia. Recent discoveries have definitely identified new gases in it, however, chief among which is argon. For all practical purposes, however, air may be considered simply a mixture of the two gases; nitrogen, which is inert and neither maintains life nor combustion; and oxygen, which performs both of these functions in a most energetic way. Air is more dense at the surface of the earth, and becomes continually more rarified as the altitude increases, until it becomes an indefinitely tenuous ether. Light as we are accustomed to regard it, the weight of a column of air one inch square is 15 pounds, and this tenuous and unfelt covering presses upon our globe with a total weight of 300,000 million tons.

Liquid air is simply air which has been compressed and cooled to what is called its critical temperature and pressure, i. e., the temperature and pressure at which it passes into another state of matter, as from a gas to a liquid. To liquefy air it is compressed until its volume is reduced to ¹⁄₈₀₀, that is to say, 800 cubic feet of air are reduced to one cubic foot. This requires a pressure of 1,250 to 2,000 pounds to the square inch.

The important step in liquefying air cheaply and on a large scale was accomplished by the discovery of what is known as the self-intensifying action. This dispenses with auxiliary refrigerants, and causes the expanding gases to supply the cold required for their own liquefaction by an entirely mechanical process. It consists in compressing the air (which produces heat), then cooling it by a flowing body of water, then passing it through a long coil of pipes and expanding the cool compressed air by allowing it to escape through a valve into an expansion chamber, where its pressure falls from 1,250 pounds to 300 pounds, which produces a great degree of cold; then taking this very cold current of air back in reverse direction along the walls of the coil of pipes, and causing said returning cold air to further cool the air flowing from the compressor to the expansion tank, and finally delivering the cold return flow to the compressors and compressing it again from a lower initial point than it started with on the first round, and so continuing this cycle of circulation through the alternating compressing and cooling stages until the air condenses in liquid form in the bottom of the expansion chamber. This successive reduction of temperature by the air acting upon itself is called self-intensification of cold, and it has an analogy in the regenerative furnace, where the augmentation of heat corresponds to the augmentation of cold in the self-intensifying action.

This principle of self-intensification was first announced by Prof. C. W. Siemens in the provisional specification of his British patent No. 2,064, of 1857, but it does not seem at that time to have been carried out with any practical result. The first embodiment of the principle in a refrigerating apparatus is by Windhausen—United States patent No. 101,198, March 22, 1870. Solvay, in British patent No. 13,466, of 1885, gave further development to the idea, and following him came the operations of Prof. Tripler, who was the first to liquefy large quantities of air and to introduce it to the American people. Lindé, Hampson and Ostergren and Berger are more recent operators in this field of self-intensification, and Lindé’s British patent, No. 12,528, of 1895, may be regarded as a representative exposition of the principle. A simplified form of the Lindé apparatus is seen in Fig. 300. C is an air compressing pump, whose plunger descending compresses the air and forces it out through valve I, pipe 2, and coil 3. The coil 3 is immersed in a flowing body of water in the condenser W, the water entering at Y and passing out at Z. The cold compressed air then passes through pipes 4 and 5, pipe 5 being arranged concentrically within a larger coil 7. The cold air flowing down pipe 5 escapes through a valve adjusted by handle 6, into the subjacent chamber L, and expanding to a larger volume, produces a great degree of cold; this cold expanded air then passing up the larger and outer pipe 7 flows back over the incoming stream of air in pipe 5, chilling it still lower than the condenser W did, and this cold return flow then passing from the top of coil 7 descends through pipe 8 to the compressing pump C, and as its piston rises, it enters the pump through the inwardly opening valve 9, and here it undergoes another compression and circuit through the pipes 2, 3, 4, 5, but it is compressed on its second round of travel at a lower temperature than it had initially, and so this circulation of air going to the chamber L, expanding, and returning over the inlet flow pipe 5, successively cooling the latter and also successively entering the compressor at a continually lower temperature at each cycle of circulation, finally issues through the valve at the lower end of pipe 5, and expands to such a low temperature that it condenses in chamber L in liquid form. Fresh accessions of air are furnished to the apparatus through valve 10 as fast as the air is liquefied. The inlet flow to the liquefying chamber is shown by the full line arrows, and the return flow to the compressor by the dotted arrows, and the explanation of the term self-intensification is to be found in the cooling of the incoming air in pipe 5 by the outflowing air in the surrounding pipe 7, and the repeated reductions of temperature at which the air is returned to the compressor.

In Fig. 301 is shown the liquefier of a modern liquid air plant, in which liquid air is being drawn into a pail from the liquefier. Liquid air evaporates very rapidly, and produces the intense cold of 312° below zero. There is no known way to preserve it beyond a limited time, for, if put in strong, tightly closed vessels, it would soon absorb enough heat to vaporize, and in time would acquire a tension of 12,000 pounds per square inch, and would burst the vessel with a disastrous explosion. If left exposed to the air, which is the only safe way to transport it, it is quickly dissipated. A shipment of eight gallons from New York to Washington for lecture purposes shrunk to three gallons in two days’ time. It may usually be kept longer than this, however, as the jarring of a railway train promotes its evaporation and loss. A small quantity, such as a half pint, will boil away in twenty-five to thirty minutes. The only way to preserve it for any length of time is to surround it with a heat-excluding jacket. The simplest and most effective means for doing this in the laboratory is to surround it with a vacuum. Fig. 302 shows a specially devised vessel for the commercial transportation of liquid air. A double walled globular vessel has between its walls air spaces and non-conducting packing. The liquid air in the interior chamber vaporizes gradually, and escaping through the outwardly opening valve at the top, expands around the air space surrounding the inner vessel. From this space it reaches the outer air by a valve at the bottom of the outer vessel. The liquid air in evaporating is thus carried around the body of liquid air in the center, and surrounding it with an intensely cold envelope, prevents the transmission of heat to the inner vessel. To withdraw the liquid air, a pipette or so-called siphon tube, shown in detached view, is substituted for the valve at the top.

FIG. 303.—SEPARATION OF LIQUID AIR INTO ITS CONSTITUENTS.

Nitrogen separation

Evaporation of Nitrogen.

Nitrous oxide separation

Evaporation of Nitrous Oxide.

Oxygen separation

Evaporation of Pure Oxygen.

FIG. 303.—SEPARATION OF LIQUID AIR INTO ITS CONSTITUENTS.

As to the uses of liquid air it may be said that up to the present time it has attained little or no practical application. There are two principal ways in which it may be utilized; one is to employ its enormous expansive force to produce mechanical power, and the other is as a refrigerant. As a means for obtaining motive power it is a fallacy to suppose that any more power can be obtained from its expansion than was originally required to make it. It is like a resilient spring in this respect, that it can give out no more power than was required to compress it. In some special applications, however, as for propelling torpedoes, where its cost is entirely subordinate to effective results, it might prove to be of value. For blasting purposes also it presents the promise of possible utilization. As a refrigerant for commercial purposes, and for supplying a dry, cool temperature to the sick room, and for the preparation of chemicals requiring a low temperature to manufacture, it might find useful application. Inasmuch as the nitrogen of liquid air evaporates first, and leaves nearly pure liquid oxygen, it may also be employed as a means for producing and applying oxygen. Good illustration of this is given in Fig. 303, in which at 1 is shown a vessel filled with liquid air. The gas first evaporating is nitrogen, and a lighted match applied to the surface of the liquid is quickly extinguished, since nitrogen does not support combustion. As the level of the liquid falls by evaporation, the remaining portions become richer in oxygen and poorer in nitrogen, and nitrous oxide gas is then given off, which supports combustion as seen at 2; and when the last portions of the liquid are being evaporated, as at 3, it is practically pure oxygen, which gives a brilliant combustion of a carbon pencil, or even of a steel spring when the latter is heated red hot. Already Prof. Pictet has formulated a plan for the commercial production and separation of the ingredients of liquid air—the nitrogen, carbonic acid, and oxygen being separated by their different evaporating temperatures with a view to applying them to various industrial uses. All of the commercial applications of liquid air, however, depend upon its cost of production, which seems at present an uncertain factor. According to the claims of some it may be produced at a cost of a few cents a gallon. More conservative physicists say that it costs $5 a gallon.

However this may be, the phenomena which it presents are both interesting and instructive. In Figs. 304 and 305 are shown some of the experiments. At No. 1 a test tube containing liquid air, from which the nitrogen has escaped, is strongly attracted by an electro-magnet, showing the magnetic quality of oxygen. At No. 2 is shown the combustion of a heated piece of steel in liquid air, which has become rich in oxygen by the evaporation of the nitrogen. At No. 3 a tin dipper, which has been immersed in liquid air, has become so cold and crystalline that it breaks like glass when dropped. At No. 4 liquid air imprisoned in a tube and tightly corked up, blows the stopper out in a few minutes with explosive effect. At No. 5 a piece of paper saturated with liquid air burns with great energy, and at No. 6 a piece of sponge or raw cotton similarly saturated explodes when ignited. At No. 7 a rubber ball floated on liquid air in a tumbler is frozen so hard that when dropped it flies into fragments like a glass ball. The white, snow-like vapor seen falling over the edges of the tumbler is intensely cold and heavier than ordinary air. At No. 8 is illustrated the preservation of liquid air by surrounding it with a vacuum in a Dewar bulb. At No. 9 a flask of liquid air is made to boil by the mere heat of the hand. A more striking experiment still of the same kind is to place a tea kettle containing liquid air on a block of ice. The block of ice is relatively so much hotter than the liquid air that the liquid air in the kettle is made to boil. At No. 10, Fig. 305, a heavy weight is suspended by a link composed of a bar of mercury frozen solid in liquid air. So hard is the mercury frozen that a hammer made of it will drive a tenpenny nail up to its head in a pine board. In No. 11 a layer of liquid air on water at first floats because it is lighter than water. As the lighter nitrogen evaporates, the heavier oxygen sinks in drops through the water. At No. 12 a tumbler of whiskey is frozen solid by immersing a tube containing liquid air in it. The frozen block of whiskey with the cavity formed by the tube is shown on the left. It is a whiskey tumbler made out of whiskey. A more sensational experiment is to substitute a tapering tin cup for the tube, then fill it with liquid air and immerse it in water. In a few minutes the tapering tin cup has frozen on its outer walls a tumbler of ice. This may be carefully removed, and the ice tumbler is then filled with liquid air rich in oxygen, which, by maintaining the cold of the ice tumbler, keeps it from melting. A carbon pencil or a steel spring heated to redness will now, if dipped in the liquid oxygen in the ice tumbler, burn with vehement brilliancy and beautiful scintillations, involving the anomalous conditions of a white hot heat and active combustion in the center of a tumbler of ice, without melting the tumbler. In experiment 13, Fig. 305, a jet of carbonic acid gas directed into a dish floating in a glass of liquid air is immediately frozen into minute flakes, producing a miniature snow storm of carbonic acid. In experiment 14 an electric light carbon heated to a red heat at its tip, is plunged vertically into a deep glass of liquid oxygen. A most singular combustion takes place. The heat of the carbon evaporates the oxygen in its immediate vicinity, and the carbon burns with great brilliancy and violence, forming carbonic acid, which is largely frozen in the liquid before it reaches the surface, and falls back to the bottom of the dish, so that the combustion is maintained and its products retained within the dish. A beefsteak may be frozen in liquid air to such brittleness that it is shattered like a china plate when struck a slight blow. The intense cold of liquid air does not destroy the vitality or germinating power of seed, but produces serious so-called burns on the flesh that destroy the tissues and do not heal for many months, and yet for a moment the finger may be dipped in liquid air with impunity because of the gaseous envelope with which the finger is temporarily surrounded.

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CHAPTER XXXIV.
Minor Inventions
and
Patents in Principal Countries of the World.

If the reader has been patient enough to have reviewed the preceding pages, the impression may have been formed that the notable inventions referred to represent all that is worth while to consider in this great field of human achievement. It would be a fallacy to entertain such a thought, for the little stars out-number the big ones, and the twigs of the tree are far more numerous than its branches. The great things in life are comparatively few and far between, and the bulk of human existence is made up of an unclassified mass of little things, sown like sands along the shore of time between the boulders of great events. So also in invention is its warp and woof made up of a multitude of little threads behind the gorgeous patterns of meteoric genius. Every hour of the day of modern life is replete with the achievements of invention. Look around the room, and there is not a thing in sight that does not suggest the material advance of the age; the books, the furniture, the carpets, the curtains, the wall paper, the clock, the mantels, the house trimmings, the culinary utensils, and the clothing, all represent creations of this century. So full is the daily life of these things, and so much of a necessity have they all become, that their commonplace character dismisses them from conspicuous notice. Take the most matter-of-fact and prosy half hour of the day, that at the time of rising, and see what a faithful account of the average man’s everyday life would present. The awakening is definitely determined by an alarm clock, and the sleepy Nineteenth Century man rolling over under the seductive comfort of a spring bed, takes another nap, because he knows that the rapid transit cars will give him time to spare. Rising a little later his bare feet find a comfortable footing on a machine-made rug, until thrust into full fashioned hose, and ensconced in a pair of machine-sewed slippers. Drawing the loom-made lace curtains, he starts up the window shade on the automatic Hartshorn roller and is enabled to see how to put in his collar button and adjust his shirt studs. He awakens the servant below with an electric bell, calls down the speaking tube to order breakfast, and perhaps lights the gas for her by the push button. He then proceeds to the bath, where hot and cold water, the sanitary closet, a gas heater, and a great array of useful modern articles present themselves, such as vaseline, witch hazel, dentifrices, cold cream, soaps and antiseptics, which supply every luxurious want and every modern conception of sanitation. His bath concluded, he proceeds to dress, and maybe puts in his false teeth, or straps on an artificial leg. Donning his shirt with patented gussets and bands, he quickly adjusts his separable cuff buttons, puts on his patented suspenders, and, winding a stem-winding watch, proceeds down stairs to breakfast. A revolving fly brush and fly screens contribute to his comfort. A cup of coffee from a drip coffee-pot, a lump of artificial ice in his tumbler, sausage ground in a machine, batter cakes made with an egg beater, waffles from a patented waffle iron, honey in artificial honey comb, cream raised by a centrifugal skimmer, butter made in a patented churn, hot biscuits from the cooking range, and a refrigerator with a well stocked larder, all help to make him comfortable and happy. The picture is not exceptional in its fullness of invented agencies, and one could just as well go on with our citizen through the rest of the day’s experience, and start him off after breakfast with a patented match, in a patented match case, and a patented cigarette, with his patented overshoes and umbrella, and send him along over the patented pavement to the patented street car, or automobile, and so on to the end of the day.

Some of the minor inventions are really of too much importance to be passed without comment. The cable car is a factor which has cut no small figure in the activities of city life. The first patent on a slotted underground conduit between the rails, with traction cable inside and running on pulleys, was that to E. A. Gardner, No. 19,736, March 23, 1858. Hallidie, in San Francisco, in 1876, directed his energies to a development of this system, and brought it to a degree of perfection and general adoption that made it for many years the leading system of street car propulsion. To-day, however, it represents but a decadent type, being largely supplanted by the superior advantages of electricity.

Passenger elevators constitute one of the conspicuous features of modern locomotion. Without them the tall office buildings, hotels, and department stores would have no existence; the Eiffel Tower would never have been dreamed of, and the expenditure of vital force in stair climbing would have been greatly augmented. The passenger elevator has for its prototype the ancient hoist or lift for mines, but in the latter half of the Nineteenth Century it has developed into a distinct institution—a luxurious little room, gliding noiselessly up and down, actuated by a power that is not seen, and supplied with every appliance for safety and comfort, such as governors, safety catches, automatic stops, mirrors and cushioned seats. The principle of the screw, of balance weights, of the lazy tongs, and other mechanical powers have each found application in the elevator, but steam, hydraulic power, and electricity constitute the moving agencies of the modern type. The patent to E. G. Otis, No. 31,128, January 15, 1861, marks the beginning of its useful applications.

Of close kin to the elevator are the fire escape, dumb waiter and grain elevator, each of which fills a more or less important function in the life of to-day.

What more ubiquitous or ingenious illustration of modern progress than the American stem winding watch! Up to the middle of the century all watches were made by hand throughout. Each watch had its own individuality as a separate creation, and only the privileged few were able to carry them. In 1848 Aaron L. Dennison, a Boston watch maker, began making watches by machinery, and the foundation of the system of interchangeable parts was laid. A small factory at Roxbury, Mass., was established in 1850, which four years later was moved to Waltham. In 1857 it passed into the hands of Appleton, Tracy & Co., and was subsequently acquired by the American Watch Co. As presenting some idea of the great elaboration involved in this art, it was estimated a few years ago that 3,746 distinct mechanical operations were required to make an ordinary machine made watch. A single pound of steel wire is sometimes converted into a couple of hundred thousand tiny screws, and another pound of fine steel wire furnishes 17,280 hair springs, worth several thousand dollars. The absolute uniformity and perfect interchangeability of parts in the American watch have been obtained by substituting the invariable and mathematical accuracy of the machine for the nervous fingers and dimming eyes of the old time watchmaker, and the American machine made watch, discredited as it was at first, stands to-day the greatest modern advance in horology.

Friction Matches.—In 1805 Thenard, of Paris, made the first attempt to utilize chemical agencies for the ordinary production of fire. In 1827 John Walker, an English druggist, made friction matches called “congreves.” In 1833 phosphorus friction matches were introduced on a commercial scale by Preschel, of Vienna. In 1845 red phosphorus matches (parlor matches) were made by Von Schrotter, of Vienna, and in 1855 safety matches, which ignited only on certain substances, were made by Lundström, of Sweden. Prior to the Nineteenth Century, and in fact until about 1833, the old flint and steel and tinder box were the clumsy and uncertain means for producing fire. To-day the friction match is turned out by automatic machinery by the million, and constitutes probably the most ubiquitous and useful of all the minor inventions.

Step into any of the great department stores and the genius of the inventor confronts you in the cash carrier whisking its little cars back and forth from the cashier’s desk to the most remote corners of the great building. The first of these mechanical carriers adapted for store service was patented by D. Brown, July 13, 1875, No. 165,473. Not until about 1882, however, was there any noticeable adoption of the system, when practical development was given in Martin’s patents, No. 255,525, March 28, 1882; No. 276,441, April 24, 1883, and No. 284,456, September 4, 1883. Go to the lunch counter, and the cash register reminds you that the millenium of absolute honesty is not yet realized. The bell punch on the street car and the burglar proof safe with its combination locks are other suggestions in the same line. The first fire proof safe is disclosed in the British patent to Richard Scott, No. 2,477, of 1801. The time lock, which prevents the safe from being opened by anyone except at a certain period of daylight, was invented by J. V. Savage, and was covered by him in United States patent No. 5,321, October 9, 1847. The practical adoption of time locks began about 1875 with the operations of Sargent, Stockwell and others, and to-day they constitute one of the most important features of bank safes and vaults, and represent a marvelously beautiful and accurate example of mechanical skill.

The Otto gas-engine, and the Ericsson air-engine are important developments in power producing motors, and the improvements in pavements and in street sweepers for cleaning them, contribute to the cleanliness, sanitation, and æsthetic values of city life. The cigarette machine, which continuously curls a ribbon of paper around a core of tobacco to form a rope, and then cuts it off into cigarettes, is an important invention in the tobacco industry, however doubtful its hygienic value to the world may be. The lightning rod has brought protection to homes and lives, and the incubator has become the hen’s wet nurse. In agriculture, the reaper has been supplemented with threshing machines, seeders, drills, cultivators, horse rakes and plows. In the farm yard appear the improved carriage and wagon, the well pump, the wind wheel, the fruit drier, the bee hive, and the cotton and cider press. In the kitchen, the washing machine, the churn, the cheese press, ironing machine, wringer, the rat trap, and fruit jar. In the house, the folding bed, tilting chair, carpet sweeper, and the piano. In heating appliances, steam and water heating systems, base burning and Latrobe stoves, hot air furnaces, gas and oil stoves. In plastics there are brick machines, pressed glass ware, enameled sheet iron ware, tiles, paper buckets, celluloid and rubber articles. In hydraulics there are rams, water closets, pumps, and turbine water wheels. In mining there are stamp mills, ore crushers, separators, concentrators, and amalgamators. In the leather and boot and shoe industry there is a great variety of machines and appliances. The paper industry, with book binding machines, and paper box machines, is a fertile field of invention. Steam boilers, metallurgical appliances, soap making, chemical fire extinguishers, fountain pens, the sand blast, bottle stoppers, and a thousand other things present themselves in miscellaneous and endless array. These are, however, only some of the things which the limitation of space precludes from individual treatment, but which are none the less important in making up the great resources of modern life, and, for the most part, represent the contributions of the Nineteenth Century not heretofore considered.

The observant and thoughtful reader finds just here occasion to inquire the meaning of this great rising tide of progress which has so distinguished the Nineteenth Century. It is largely due to the Patent Law, which justly regards the inventor as a public benefactor, and seeks to make for him some protection in the enjoyment of his rights. If a man be in the possession of a legacy by the accident of birth, the law of inheritance rules that it is rightfully his. The finding of a thing, whether by jetsam, flotsam, or the lucky accident of a first discovery, this also makes good his title, if there be no other owner. There is, however, a right of property which is higher than all others, and in which there is coupled with the possession of the thing the sacred function of its creation. The right of a mother to her child is of this nature, and like unto it is the right of the inventor to the creation of his genius. In the last two centuries of the world’s history this right has been recognized by an enlightened civilization, and provision made for its enjoyment in the grant of patents, and if there be any right more strongly entrenched than another in the eternal verities of equity and justice it is this. Our first crude patent law was enacted in 1790, but not until 1836 was the present system adopted. Our own and comparatively new country has, therefore, not yet had a hundred years of existence under our present Patent System, and yet to-day it outstrips the world both in its material resources and in its wealth of patented inventions. The accompanying diagram, Fig. 306, illustrates in a graphic way just what relation the United States bears to the other leading countries of the world in the matter of patents granted, and when it is remembered that under our system a patent can only be granted for a new invention, while in some of the other countries it is not essential to the grant, the richness in invention of the United States, with its six hundred and fifty thousand patents, can be better appreciated. This is a greater number than has been issued by Great Britain and France put together. Connecticut is the most productive State in invention in proportion to its people, and Edison is the most prolific inventor. From 1870 to 1900 he has taken 727 United States patents, and there are from twenty-five to thirty other American inventors each of whom has taken 100 or more patents.

The year 1790 was notable in two events, the birth of our patent system and the death of Benjamin Franklin. That grand old philosopher, with a prescience of future greatness to come from the genius of the inventor, is said to have expressed the wish before he died that he might be sealed up in a cask of old Madeira and be brought to life a hundred years in the future, that he might witness the growth of the world. Who can tell what his emotions would be if he were with us to-day? It is said, when he first saw the fibres of the string diverge, and the spark pass from the cord of his kite, and the lightning was for the first time obedient to the will of man, that he uttered a deep sigh and wished that that moment were his last. To this poor knowledge of electricity he would now have added all the wonders and powers of the telegraph, the dynamo, the telephone, and the great modern electrical science; to his primitive hand press he would have contrasted the Octuple perfecting press, turning out papers at the rate of 1,600 a minute; his modest type-setting case would be replaced by a great array of linotype machines, and he would find several acres of woodland sacrificed to produce the wood-pulp paper of a single edition of a New York daily. Would he not realize indeed that truth is stranger than fiction, and fact more wonderful than fancy’s dream!

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CHAPTER XXXV.
Epilogue.

Whatever the future centuries may bring in new and useful inventions, certain it is that the Nineteenth Century stands pre-eminent in this field of human achievement, so far excelling all other like periods as to establish on the pages of history an epoch as remarkable as it is unique. Never before has human conception so expressed itself in materialized embodiment, never has thought been so fruitfully wedded to the pregnant possibilities of matter, never has the divine function of creation been so closely approximated, never has such an accretion of helpful instrumentalities and material resources been added to the world’s wealth—not merely the miserly and inert wealth of gold and gems, but the wealth of an enlarged human existence. This life itself is but a limited span; beginning in infancy, expanding to highest achievement in middle age, and declining at the end, it quickly passes away, and another generation follows. Growth and decay with all living things mark the immutable law of nature, and the inevitable fate of mortality. The rose blossoms into beauty, fades, and decays. The bird in the air, and the beast in the field, each plays his part and passes to the great unknown, leaving no record; man himself is mortal, but his work is immortal. The inspired conception of his best thought, the materialized embodiment of his work in useful agencies, and the subjugation of the laws of nature to his service, all endure and live forever in his inventions. These partake of the breath of life, and in their immortality are of kin to the soul. Cities may grow up and vanish, civilizations may decay, and man himself may degenerate, but the principle of the lever and the screw, once discovered, is for all time perfect, invariable and immortal. Every invention made is another permanent gift to posterity. All of enduring wealth that the present gets from the past are its ideas reduced to a working basis. All else is but dross, or evanescent dreams which vanish into oblivion in the light of a larger knowledge. But ideas wrought into practical, substantive things, tried and proven true, these are inventions—immortal creations—and of these the Nineteenth Century has borne fruit in paramount abundance, and this legacy it now bequeaths to the coming century.

To follow conventional methods, the final chapter of a book should be an “In conclusion” with a “finis” and a dismantled torch, but the history of invention will ever be a continued story. There is no end in this field. The trusteeship of the Twentieth Century man is great, and great his responsibilities; but his restless and dominant spirit knows no decadence, and his mental endowment and material equipment, without parallel in history, are a guarantee of future achievements. Will not the chemist learn how to produce electricity direct from the combustion of coal, or solve the problem of the synthesis of food? Will not the American continent be parted by an inter-oceanic canal, or the rough waters of the English Channel be avoided with a submarine tunnel? May not a ship canal through France to the Mediterranean give to that country the connected enjoyment of riparian rights, without passing the frowning battlements of Gibraltar, or might not a tunnel under the Straits of Gibraltar put Europe and Africa in direct railway communication? The relation of electricity to life is a field of pregnant possibilities, and may we not also learn to swap the surplus heat of summer for the winter’s cold, and by an equalization of their two extremes bring eternal spring and joy to the animated world? Shall we not yet stand on the North Pole, or looking away into space may we not extend a neighborly welcome to our brothers in Mars, if any there be? It is permitted to dream in this field, for it is this reaching out into the unknown that plats the boundaries of an extended world, and adds to the possessions of man.

The old man in his dreams of the past rejoices in his achievements, for he has stolen the fires of Prometheus and forged anew the thunderbolts of Jove for the arts of peace. Delving into the secret recesses of the earth, he has tapped the hidden supplies of nature’s fuel, has invaded her treasure house of gold and silver, robbed Mother Earth of her hoarded stores, and possessed himself of her family record, finding on the pages of geology sixty millions of years’ existence. Peering into the invisible little world, the infinite secrets of microcosm have yielded their fruitful and potent knowledge of bacteria and cell growth. Pain has been robbed of its terrors by anæsthesia; the heat of the sun has been brought down in the electric furnace, and the cold of inter-stellar space in the ice machine and liquid air. With telescope and spectroscope he has climbed into limitless space above, and defined the size, distance, and constitution of a star millions of miles away. The north star has been made his sentinel on the sea. The lightning is made his swift messenger, and thought flashes in submarine depths around the world. Dead matter is made to speak in the phonograph, the invisible has been revealed in the X-Rays, coal has been made his black slave, steam the breath of the world’s life, and all of nature’s forces have been made his constant servants in attendance.

With such a retrospect, the sage of the Nineteenth Century may lie down to quiet rest, with an assuring faith that what God hath wrought is good, and what is not may yet be.

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