Inventors at Work, with Chapters on Discovery

Interchangeability Old and New.

The cheap duplication of products, so wonderfully expanded of late years, had its germ long before the Christian era, when in Babylonia a builder first made bricks in a mold, and took care by careful measurement to keep to uniform dimensions in his output. Because any brick matched any other from the same mold, he introduced a new beauty and regularity in architecture, he made it easy to extend or repair a wall, a gateway, a battlement. So it was afterward with the tiles, also made in molds, which were laid as floors or roofs; and the piping, likewise molded, for water-supply or drainage. To-day when a housekeeper replaces her worn-out stove-linings, and a printer increases his stock of type, they enjoy a direct inheritance from the first molders of bricks and tiles, cups and bowls. In a modern factory vast sums are expended in producing the original patterns, molded or copied perhaps ten million times, so that their cost, in so far as represented in each manufactured hook or lever, is next to nothing. Much expense, also, is entailed in making the jigs which guide the tools used in lathes or milling machines to turn out the cases of voltmeters, or a complicated valve-seat. A jig may cost a hundred dollars and its use may require rare steadiness of hand, the utmost keenness of eye; all the while the operator’s wife, at home, avails herself of an aid based on the very same principle. What else is the paper pattern according to which she cuts out a collar, an apron, a baby’s bib?

In machinery the first introduction of an interchangeability of parts was by General Gribeauval, in the French artillery service, about 1765. He reduced gun-carriages to classes, and so arranged many of their parts that they could be applied to any carriage of the class for which they were made. These parts were stamped, not forged. The next step in this direction was taken in America and, as in France, its aim was to improve instruments of war. Eli Whitney, famous as the inventor of the cotton gin, secured a contract from the United States Government for 10,000 firearms. These he manufactured almost wholly by stamping. He introduced machinery for shaping and, as far as then feasible, the finishing of each part. He also employed a system of gauges, by which uniformity of construction was assured for every gun produced. Next came J. H. Hall, of Harper’s Ferry, Virginia, who in 1818 made every similar part of a gun of such size and shape as to suit any other gun, improving some details of importance.

The modern designer of tools, implements and machines takes care that the parts upon which wear chiefly comes are easily removable so as to be cheaply replaced. A worn out plowshare is renewed for a dollar or two, keeping the plow as a whole substantially new. Should the pinion of a watch be destroyed by accident, it is duplicated from Waltham or Elgin for a few cents.

To-day rods, wires, screws, bolts, tubes, nails, sheets of metal, are made in standard sizes. Much the same is true of rails for railroads, girders, eye-bars for bridges, and the like. Thus the product of any factory or mill may be used to piece out or to repair work turned out by any other similar concern. Yet more, if a subway or a tunnel is to be built in a hurry, two or more steel-works may co-operate in furnishing beams, columns, or aught else, with no departure from ordinary gauges. Steel works in Pennsylvania have produced every detail for a bridge erected in Africa, a factory in Germany, a stamp mill in Canada. At the World’s Congress of electricians held in Chicago in 1893, units were adopted as international standards, a noteworthy step toward adopting universal standards in all branches of engineering. Here progress is to some extent held back by firms and corporations that produce patterns not always worthy of defence. Standard forms and dimensions, especially in manufactures for a world-market, are only decided upon after thorough discussion, so that they are judiciously chosen. Among feasible shapes and sizes for rails, columns, girders, and the rest, one is usually best, or a few are best. Why not exhaust every reasonable means of ascertaining which these are for specific tasks that they may be freely chosen? Then if individuality prefers its own different designs, let it do so knowing what the indulgence costs.

A Test Shows How Concrete May be Cheaply Strengthened.

Measurements may be conducted in the strict spirit of scientific research, not immediately directed to industrial ends. Methods thus perfected are more and more being adopted for large questions of industry. Let an example be presented from the field, briefly touched upon in this book, of concrete as a material for the builder. Says Mr. C. H. Umstead of Washington, Pennsylvania:—

“Many thousands of tons of the finer grades of stones from the crushers all over the country are rejected by engineers for use in concrete foundations and walls, sand being preferred at greatly increased cost. I prepared seventy-two three-inch cubes with quartz sand and with varying proportions of crushed stone which was going to the dump as unfit for foundation work, and submitted them to crushing tests at periods of fourteen and twenty-eight days. The proportion of Portland cement was constant.”

From Mr. Umstead’s table of results the following figures are chosen; on comparing those for the first and third cubes they show that a gain in strength of forty-three per cent, followed upon using six pounds of crusher refuse instead of five and one half pounds of sand.

So much for the value of a test in the improvement of an important manufacture.

Mr. Umstead’s full report appeared in 1903, in the third volume of bulletins published by the American Society for Testing Materials. This Society, whose secretary is Professor Edgar Marburg of the University of Pennsylvania, Philadelphia, is affiliated with the International Association for Testing Materials, one of the most important agencies in existence for providing the engineer with trustworthy data.

Industrial Uses of Measurement.

Measurement industrially is taking on a new and rapidly extending scope. It is of great moment that a railroad or a steamship, a factory or a mill, should be built of the best materials in the most economical way, that it should be equipped with the most efficient boilers, engines, machines, and lamps: in effect, that every dollar be expended for the utmost possible value.

At Altoona the Pennsylvania Railroad Company has a laboratory for testing the materials which go into its roadbed, bridges, tracks, rolling stock, buildings, telegraph, and signal systems. Every gallon of oil, each incandescent lamp, car axle, or boiler plate accepted by the Company must pass a due test in a continuous series of competitive examinations. The huge scale of such a Company’s purchases, the strains placed upon its equipment by a service growing in extent and in speed, make this course indispensable. Take another case, this time in New York, at the power-house of the Interborough Company in West 59th Street. There every day a fair sample of the coal brought to the dock is burned, and its heat-units ascertained as a basis for payment. With a consumption which may rise to 1500 tons a day this precaution is obligatory.[30]

On quite other lines, equally important, the ascertainment of values proceeds at laboratories thoroughly organized for the purpose by staffs at the service of the public. In the United States the first in rank of such laboratories are grouped at the Bureau of Standards in Washington. At leading universities and technological institutes throughout the Union are other laboratories well equipped for chemical, physical, and engineering tests. At the Massachusetts Institute of Technology in Boston, for example, is an Emery testing apparatus for making compression tests of specimens up to eighteen feet in length, for tension specimens up to thirteen feet. In Europe analogous institutions are supplemented by the Board of Trade Laboratories in London, the Laboratoire Central in Paris, the Reichsanstalt in Berlin. The Electrical Testing Laboratories, a joint-stock concern, has been established in New York, at Eightieth Street and East End Avenue, for similar tasks in so far as they come within the electrical field. Its direction in ability and character is authoritative. Here is some of the best apparatus in the world for tests of the permeability of magnet iron, of the light from incandescent, arc, or other electric lamps, of gas-burners and mantles, of the extent to which reflectors and globes fulfil their purpose, and so on.

It is altogether probable that this concern will be copied in every other large city of the Union. When an electrical plant is installed it is not enough that the specifications be drawn with care, it is necessary that verifications of quality follow upon delivery of dynamos, motors, lamps, and all else. Tests should be continuous: let us suppose that for a specific task of illumination Nernst lamps are selected. All very well, but the question is, What quality has each lamp? Buyers in cases of this kind are more and more referring rival manufactures to tests which settle, as in a court of final appeal, differences upon which they themselves are incompetent to pass. Not only in sale but in production these tests are of the first importance. If a copper refinery turns out from the same batch of crude metal two samples which vary by a thousandth in electrical conductivity, it is worth while knowing every detail which may explain how the better sample was produced. So likewise in the drawing of wire, the alloying of lead with other metals for anti-friction bearings, and so on.

It is altogether likely that recourse to authoritative tests will soon become general. Before many years elapse we may see private and public laboratories multiplied for the comparison of building and road-making materials, fuel, boilers, engines, machines, lubricants, finished goods of all kinds. In the textile industry, for instance, much is said about the waste entailed in mixing sound wool with shoddy, long staple cotton with short inferior brands. Let pure and adulterated fabrics be compared in resistance to wear, and let the effects of scouring, bleaching, dyeing, and mechanical washing be measured. In another field Professor W. O. Atwater has done much to ascertain the nourishing value of foods: his labors might well be extended full circle, not omitting tests of popular medicaments and common drugs.

Expert Planning and Reform.

To-day engineers of mark are engaged not only to plan a power-house, a flour mill, a steel works or other vast installation, but also to examine industrial plants established long ago and enlarged from time to time in an unsystematic way. Armed with scales, pressure-gauges, indicators, voltmeters, they ascertain the cost of a horse-power-hour, of making a pound of flour, copper wire, or aught else. They note how speeds may be heightened with profit, as by using suitable brands of high-speed steels. They suggest how a pattern may be adopted in the foundry which will lessen machining; how by-products now thrown away may be turned to account. They point out how quality may be improved by the adoption of new machines which may, furthermore, demand unskilled instead of skilled attendance. They may advise, from a wide outlook on the whole field of American experience, a method for equalizing output throughout the day and throughout the year, as when a central-lighting station sells current at a large discount during the hours when no lamps are aglow, so that ice may be manufactured at such periods, or batteries restored for use in automobiles and motor-boats. Mr. Wilson S. Howell, of New York, a few years ago became convinced that a neglected branch of economy in central lighting stations was the maintaining a uniform voltage. He succeeded in reducing fluctuations in many plants to the unexampled figure of four per cent. The result was that he lowered the current necessary for an Edison lamp from 3.6 watts to 3.1 watts per candle-power, a saving of one seventh. Mr. M. K. Eyre, another well-known engineer, once took charge of a lamp factory in Ohio. In four months he had reduced cost forty per cent. while producing a lamp of the best quality. An electric lighting and power property which for years had been unprofitable was placed in the hands of Messrs. J. G. White & Company of New York, an engineering firm of the first rank. Within a few months the property was earning a substantial surplus; the ratio of operating to gross earnings was reduced about thirty per cent., and the gross earnings showed an increase over corresponding months of the previous year of nearly forty per cent. Economies quite as striking have been effected by the firm of Messrs. Dodge & Day of Philadelphia. On request investigators of this stamp, whose aim is to abolish waste and promote efficiency, go beyond mechanical and engineering details. They may point out how needed working capital may be obtained, how best to extend sales, and possibly how an economical consolidation with other similar plants may be effected. Almost invariably it is found imperative to recast the bookkeeping methods, especially with regard to ascertaining the cost of production in each department. Drawing upon experience recommendations may follow as to premium plans of paying wages, and other methods of identifying the interests of employers and employed.[31] Approved schemes for the comfort and welfare of work people are also suggested by counsellors thoroughly aware that contentment is great gain, that pure air, good light, and the utmost feasible safety, contribute to the balance sheet not less than the quickest lathe tools or the best wound dynamo.

CHAPTER XVIII
NATURE AS TEACHER

Forces take paths of least resistance . . . Accessibility decides where cities shall arise . . . Plants display engineering principles in structure. Lessons from the human heart, eye, bones, muscles, and nerves . . . What nature has done, art may imitate,—in the separation of oxygen from air, in flight, in producing light, in converting heat into work . . . Lessons from lower animals . . . A hammer-using wasp.

Beyond their unending study of forms and properties, their constant weighing and measuring, the inventor and his twin-brother, the discoverer, have a gainful province which now for a little space will engage our attention. This province is nothing else than Nature, which begins by offering primitive man stones for hammers, arrowheads, knives; sticks to serve as clubs, paddles, harrows or tent-poles. We may well believe that the lowest savages have always exercised some degree of choice even here; it would be the soundest and sharpest stone that they picked up when a rude axe was needed. Should only blunt stones be found, then in giving one of them an edge was taken a first step in art, rewarded with a tool as good as the axe found ready to hand in some earlier quest. Nature is not only a giver of much besides stones and sticks, she is virtually a great contriver whose feats may incite the inventor to reach her goals if he can; his path will probably differ widely enough from hers as he arrives at success.

Forces Take the Easiest Paths.

When one drop of rain meets another, and they join themselves to thousands more on the crest of a hill, they need no guide posts to show them the easiest course to the valley. They simply take it under the quiet pull of gravity. When a bolt of lightning darts across the sky, its lines, chaotic as they seem, are just the paths where the electric pulses find least obstruction. If a volcano, which has boiled and throbbed for ages, at last opens a chasm on a hapless shore, as that of Martinique, we may be sure that at that point and nowhere else the mighty caldron’s lid was lightest. A cavern in Kentucky, or Virginia, slowly broadening and deepening through uncounted rills which dissolve its limy walls, comes at last to utter collapse: the breach marking exactly where an ounce too much pressed the roof at its frailest seam. In these cases as in all others, however complex, matter moves inevitably in the path of least resistance. To imitate that economy of effort is from first to last the inventor’s task.

Cities and Roads.

Rains, winds and frosts, in their sculpture of the earth have each taken the easiest course; in so doing they have incidentally marked out the best paths for human feet, have pointed to the best sites for the homes of men. The stresses of defence may rear a pueblo on the peak of a perpendicular cliff in New Mexico, but Paris and London, like Rome, must have all roads leading to their gates; and the easier and shorter these roads, the bigger and stronger the city will become. Where New York, Montreal, Chicago, and Pittsburg now stand, the Indians long ago had the wit to found goodly settlements. They knew, as well as their white successors, the advantages of paths readily traversed, and no longer than need be. In this regard there was an instructive contrast at the outset of railroad building in England. A leading engineer, who planned some of the earliest English railways, had strong mathematical prepossessions: he endeavored to join the terminals of his routes by lines as nearly straight as he could. George Stephenson, for his part, had no mathematical warp of any kind, but instead much sound sense; his lines followed the courses of rivers and valleys, and kept, as much as might be, to the chief indentations of the sea. His roads deviated a good deal from straightness, but they did so profitably; whereas the lines of his academic rival, disrespecting the hints and indications of nature, were much less gratifying from an investor’s point of view. If a traveler takes the New York Central and Hudson River Railroad from New York to Buffalo he goes north for 143 miles, to Albany, before he begins to travel westward at all. Yet this line, keeping as it does to the well-peopled levels of the Hudson and Mohawk Valleys and serving their succession of cities, towns, and villages, enjoys the best business, and makes better time between its terminals than any rival route, because it passes around instead of over its hills and mountains. By way of contrast we turn to the railroad map of Russia and observe how Moscow and St. Petersburg are joined by a line which follows the road which it is said that Peter the Great, with military exigencies in view, laid down with a pencil and ruler.

Engineering Principles in Vegetation.

If the engineer has many a golden hint spread before him in the hills and dales, the streams and oceans of the world, not less fruitful is the study of what takes place just beneath the surface of the earth where the roots of grain and shrub, reed and tree, take life and form. Plant a kernel of wheat in the ground and note how its rootlets pierce the soil, extending always from the tip. They need no gardener or botanist to bid them lengthen and thicken where food chiefly abounds. In an arid plain of Arizona a vine, in ground parched and dry, goes downward so far, and spreads its fibrils so much abroad, as soon to show ten times as much growth below the drifting sands as above them. In fertile, well-watered soil the same vine descends less than half as far, and yet with more gain. A bald cypress in a swamp of Florida responds to different surroundings with equal profit. Finding its food near the surface its roots take horizontal lines, at no great depth in the soil. Every wind that stirs these roots but promotes their thrift and strengthens their anchorage. A wealth of sustenance floats in the swamp water. In seizing it and being thereby fed, the roots develop “knees”; these brace the tree so firmly against tempests as to win admiration from the engineer. When the progeny of this cypress grow on well-drained land, the knees do not appear, while the roots within a narrowed area strike deep. Thus simply in doing what its surroundings incite it to do, the tree acts as if it had intelligence, as if it consciously saw and chose what would do it most good.

Lumbermen in the North observe much the same responsiveness. In a grove of pines they see that the trees which stand close together are tall and cylindrical. When all the pines but one in a cluster are cut down, that one will speedily thicken the lower part of its trunk by virtue of the increased action of the winds, just as a muscle thickens by exercise.

The Gain of Responsiveness.

So also is there responsiveness when we look upon the life of plants in the large. As the traits of a shrub or tree are borne into its seed many a thousand impulses are merged and mingled. Little wonder that their delicate accord and poise should be slightly different from those of the seeds from which the parents sprang. Let us suppose these parents to be cactuses, and that the offspring displays an unusually broad stem, of less surface comparatively than any other plant in its group. In a soil seldom refreshed by rain, this cactus has the best foothold and maintains it with most vigor. Sandstorms which kill brethren less sturdy, strike it in vain, so that its kind is multiplied. Wherever such a new character as this gives a plant an advantage, it holds the field while its neighbors perish. Thus arises a high premium on every useful variation, be it in new stockiness of form, an acridity which repels vermin, or a strength which readily makes a way through sun-baked earth. Hence such new traits are, as it were, seized upon and become points of departure for new varieties, and in the fullness of time, for new species. About a hundred years ago a gardener imagined a tuberous begonia, and then proceeded step by step toward its creation by breeding from every flower that varied in the direction he desired. This man, and all his kindred who have added to our riches in cultivated blooms, have no more than copied the modes of nature which, at the end of ages, bestows as free gifts every wildflower of the field and hedgerow. If the botanist of to-day is the master of a plastic art, so is the cattle-breeder who chalks on a barn-door the outline of a beeve he wishes to produce, and then straightway plans the matings which issue in the animal he has pictured. Artificial selection, such as this, is after all only imitation of that natural selection which has derived the horse from a progenitor little larger than a fox, in response, age after age, to changing food, climate, enemies, and the needs of his human master.

Scope for Imitation.

Fields remote from those of the naturalist are just as instructive. The inventor sets before himself an end with conscious purpose, and then seeks means to reach that end, but at best his methods may be wasteful and imperfect. Nature, with unhasting tread, acting simply through the qualities inherent in her materials, through their singular powers of combination, of mutual adaptability, shows the discoverer results which to understand even in small measure tax his keenest wit, or displays to him structures at times beyond his skill to dissect, much less to imitate. Mechanic art, indeed, is for the most part but a copy of nature, as when the builder repeats the mode in which rocks are found in caves, in ridges at the verge of a cliff, or in the stratifications which underlie a county, all conducing to permanence of form, to resistance against abrading sand or dissolving waters. What ensures the stability of a lighthouse but its repetition of a tree-trunk in its contour? Engines and machines recall the animal body, grinding ore much as teeth grind nuts, lifting water as the heart pumps blood through artery and vein, and repeating in mechanism of brass and steel the dexterity of fingers, the blows of fists. When an inventor builds an engine to drive a huge ship across the sea, he has created a motor vastly larger than his own frame, but much inferior in economy. At a temperature little higher than that of a summer breeze the human mechanism transmutes the energy of fuel into mechanical toil: for the same duty, less efficiently discharged, the steam engine demands a blaze almost fierce enough to melt grate bars of iron.

Heat is costly, so that its conservation is an art worth knowing. In the ashes strewn and piled on burning lava nature long ago told us how heat may be secured against dissipation. Other of her garments, as hair and fur, obstruct the escape of heat in a remarkable degree, and so does bark, especially when loosely coherent as in the cork tree. Feathers are also excellent retainers of heat, and have thereby so much profited their wearers, that Ernest Ingersoll holds that the development of feathers has had much to do with advancing birds far above their lowly cousins, the reptiles clad in a scaly vesture.

Strength of the Cylinder.

As we look back upon the past from the vantage ground of modern insight we see that men of the loftiest powers could be blind to intimations now plain and clear. Many a time have designers and inventors paralleled, without knowing it, some structure of nature often seen but never really observed. All the variety and beauty of the Greek orders of architecture failed to include the arch; yet the contour of every architect’s own skull was the while displaying an arched form which could lend to temple and palace new strength as well as grace. The skeleton of the foot reveals in the instep an arch of tarsal and metatarsal bones, with all the springiness which their possessor may confer upon a composite arch of wood or steel. Modern builders, whether wittingly or not, have taken a leaf from the book of nature in rearing their tallest structures with hollow cylinders of steel. What is this but borrowing the form of the reed, the bamboo, a thousand varieties of stalk, one of the strongest shapes in which supporting material can be disposed? Pass a knife across a blade of pipe or moor grass and you will find a hollow cylinder stayed by buttresses numbering nearly a score. More elaborate and even more gainful is the way in which tissue grows in the columns of dead-nettles and bulrushes. The bones in one’s arms and legs resemble the hollow cylinders of which these stalks show instructive variations, so that without going beyond his own frame the designer could long ago have learned a golden lesson. How bone is joined to bone is scarcely less remarkable, as in the braces of the thigh bone as it joins the trunk. As bones move upon each other all shock is prevented by a highly elastic cushion: the springs of vehicles, the buffers of railroad trains, but repeat the cartilages in the joints of their inventors.

In the theodolite and sextant, in the geometric lathe of the bank-note engraver, are ball-and-socket joints allowing motion in any plane. Equally free in their movements are the shoulder and hip joints, while their surfaces are lubricated by a delicate synovial fluid supplied just as it is wanted. When pumps first received valves to direct their flow in one direction, their inventor was no doubt gratified at his skill. In the heart within his own breast, in his veins and arteries, were simple valves engaged in a similar task as they directed the currents of his blood. In pumps such as are common in farm-yards, the action is jerky, the stream flowing and ebbing from moment to moment as the arm rises and falls. The tide of human blood would have the same uneven pulse were it not for the elasticity of its arterial walls. Their elasticity serves to equalize the flow, much as the air does in large chambers on pumps for mines or waterworks.

The Heart and the Built-up Gun.

Examination of the heart brings out a principle in its structure closely paralleled in modern invention. Guns of old were cast or forged as ordinary columns or shafts are to-day, the strength of the metal being virtually uniform throughout when the guns were at rest on their trunnions. As explosive charges more and more powerful were employed, these guns gave way, the pressure of the exploding gases stretching the metal at the bore to rupture, before the outer metal could add its resistance. A modern built-up gun is made up of a series of, let us say, four cylinders: the first, of comparatively small bore and thickness, is innermost. It is cooled to as low a temperature as possible, when a second cylinder is slipped over it red-hot to form a tight fit. Both masses of metal are now slowly cooled, when a third red-hot, closely fitting cylinder is passed over them. All three united masses are now cooled, when the fourth and widest cylinder of all, red-hot, is passed over these three inner tubes, and the whole gun is allowed gradually to fall in temperature. When this process is completed the inner parts of the gun, by virtue of the shrinkage in the metal as it cooled, are under severe compression, while the outer parts are in as extreme a state of stretch or tension. When such a gun is fired its inner cylinders oppose much greater resistance to the outward pressure of the exploding gases than did the walls of the old-time guns. The strength of the old guns was uniform throughout when they were doing nothing, and very far from uniform at the instant of firing; a built-up gun, on the contrary, has uniform strength in its every part just when that uniformity is wanted, at the moment of explosion. The built-up gun therefore uses projectiles vastly heavier and swifter than those of former times. Its structure, made up of cylinders successively shrunk one upon another, resembles that of the heart, whose two inner parts have their fibres wound somewhat like balls of twine, these in turn being tightly compressed by a covering of other fibres. The heart has to resist no such explosive force as arises within a gun, but in its propulsion of blood through the arteries and veins it has to exert great pressure, with no rest throughout a lifetime. This pressure is uniformly distributed throughout the muscular tissue by a structure which, as engineers would say, has its outer layers in tension and its inner layers in compression. During twenty-four hours the labor of an average human heart is equal to lifting two hundred and twenty tons one foot from the ground.

What building-up does to strengthen the gun has been repeated in the case of the circular saw: driven at a high speed it becomes so highly heated at its periphery that the resulting expansion may crack the metal in pieces. In an improved method of manufacture the saw is hammered to a compression which gradually increases from rim to centre. In this way the tendency of the periphery to fly apart is withstood by the compressive forces at the central portion of the disc.

This ingenious treatment of metal for guns and saws reminds us of a familiar resource in carpentry, illustrated on page 36. An ordinary book-shelf, if fairly long and not particularly stout, bends beneath its burden and may at last slip out from its mortices and fall with injury to its books. At the outset this is prevented by bending the shelf to convexity on its upper surface. Then a heavy load no more than brings the shelf to straightness, so that the books remain in their places with both safety and sightliness. Here a principle is involved worth a moment’s pause. An inventor asks, What effect will a working load exert which it is desirable to lessen or withstand? He gives his structure a form opposite to that which will result from an imposed burden, so that when at work his structure, a shelf, a cylinder, a saw, will assume its most effective shape.

The Eye and the Dollond Lenses.

From childhood we are familiar with the triangular prisms of glass which break a sunbeam into all the hues of the rainbow. A lens is a prism of circular form, and has, equally with an ordinary prism, the power to show rays of all colors. This was for a long time a source of error and annoyance in telescopic images. Sir Isaac Newton from some rough and ready experiments concluded that the trouble was beyond remedy, yet all the while his own eyeballs were transmitting images with little or no vexatious fringe of color. Let us note how Dollond set about a task which Newton deemed impossible. He knew, what Newton did not know, that crown glass disperses or scatters light only half as much as does flint glass, so he united a lens of the one to a lens of the other, and obtained a refracted or bent beam of light almost unchanged in its whiteness. Of course, in this combination there was an increased thickness of glass, but its doubled absorption and waste of light was a small drawback compared with the advantage of almost wholly excluding the tinted fringe which had so long vexed astronomers. In the eyeball are first a crystalline lens, next an aqueous humor, third a vitreous humor; these three so vary in their qualities of refraction and dispersion as to render images quite free from color fringes. Compound lenses on the Dollond principle, repeating the structure of an eyeball, are used in all good telescopes, microscopes, and cameras, and are now executed in varieties of Jena glass which bring perturbing hues to the vanishing point. In their achromatic, or color-free, lenses and their cameras, or dark chambers, our photographic instruments much resemble the eye. Indeed, it may be that when we see an object the impression is due to a succession of fleeting photographs, following each other so rapidly on the retina as to seem a permanent picture. The eye, furthermore, is stereoscopic; by uniting two images seen from slightly differing points of view, it enables us to judge of size, solidity, and distance.

Limbs and Lungs as Prototypes.

Long before there was a philosopher to classify levers into distinct kinds, the foot of man was affording examples of levers of the first and second orders, and his fore-arm of a lever of the third order. Ages before the crudest bagpipe was put together, the lungs by which they were to be blown, and the larynx joined to those lungs, were displaying a wind instrument of perfect model. The wrists, ankles, and vertebrae of Hooke might well have served him in designing his universal joint. Indeed weapons, tools, instruments, machines, and engines are, after all, but extensions and modified copies of the bodily organs of the inventor himself.

Canals have called forth the ingenuity of an army of engineers; ever since the first heart-throb, the circulation of the human blood was exemplifying a system in which the canal liquid and the canal boats move together, making a complete circuit twice in a minute, distributing supplies wherever required, and taking up without stopping return loads wherever they are found ready. The heart, with its arteries and veins, forms a distributing apparatus which carries heat from places at which it is generated, or in excess, to places where it is deficient, tending to establish a uniform, healthful temperature. To copy all this, with the ventilating appliances prefigured in the lungs, is a task which in our huge modern buildings demands the utmost skill of the architect and engineer.

Postal and Telephonic Service.

In a great city each branch post office is connected solely with headquarters, to which it sends its letters, papers, and parcels, receiving in return its batches for local distribution. For each branch office to communicate with every other would be so costly and cumbrous a plan as to be quite impracticable. Our postal method is adopted in every telephonic service; Z communicating with D or M only after he has had his line joined to the central switchboard which connects with every telephone in the whole system. All this was prophesied in the remote ancestry of both postmasters and electricians as their nerves took the paths of what is in effect a complete telegraphic circuit, with separate up and down lines and a central exchange in the brain,—that prototype of all other means of co-ordination.

Fibrils of the Ear and Eye.

Pianos, organs, and other musical instruments yield their notes by the vibration of strings, pipes, or reeds of definite size and form. Across the larynx, the box-like organ of the throat, the vocal cords vibrate in an identical way. When we sing a note into an open piano, the string capable of giving out that note at once responds. Helmholtz believed that in the ear the delicate, graduated structures, known as the rods of Corti, vibrate in the same way when sound-waves reach them, giving rise to auditory impressions. Analogous in operation are the fibrils of the eye which respond to light-waves of various length and intensities. The human eye has muscles which modify its globularity, rendering its lenses more or less convex. A cat has a higher degree of this kind of ability, so that it can dilate its pupil so much as to see clearly in a feeble light. A man who remains in a darkened room so rests his nerves of vision that in four or five hours he can readily discern what would be unseen were he newly brought into the darkness.

The Electric Eel.

Not only in the frame of man, but in the bodies of the lower animals, are suggestions which ingenuity might well have acted upon in the past, or worthily pursue in the future. The science of electricity was born only with the nineteenth century because the gymnotus, or electric eel, had not been understandingly dissected. Its tissues disclose the very arrangement adopted by Volta in his first crude battery, namely, layers of susceptible material surrounded by slightly acid moisture. The characteristics of this eel have their homologies in the human body; in the muscles which bend the fore-arm, for example, are nearly a million delicate fibrils comparable in structure with the columnar organs of the gymnotus. These fibrils are so easily excited by electricity as to denote an essential similarity of build. Both the columnar layers of the eel and the fibrils of human muscle are affected in the same way by strychnine and by an allied substance, curare.

A Beaver Tooth and the Self-Sharpening Plow.

The frames of other animals furnish forth a goodly round of analogies with recent products of mechanical ingenuity. A beaver tooth might well have been the model for a self-sharpening plowshare, widely used throughout the world. This tooth has a thin outer layer of hard enamel, within which, dentine, less hard, makes up the rest of the structure. Gnawing wears the dentine much more than the enamel, so that the tooth takes on a bevel resembling that of the chisel which pays frequent visits to a carpenter’s oil-stone. The scale of enamel gives keenness, the dentine ensures strength, so that the tooth sharpens itself by use, instead of growing dull. Much the same structure is repeated in a plowshare by chilling the underskin of the steel to extreme hardness, while the upper face of the share is left comparatively soft. As it goes through the ground the upper face wears away so as to yield a constantly sharpened edge of the thin chilled under metal. Thus the heavy draft of a dull share is avoided without constant recourse to the blacksmith for re-sharpening.