Various modifications have been made in the hydraulic forms. In place of steam, electricity was introduced to control the hydraulic operation.

Again, an electric motor has been invented to be placed on the car itself, with connected gearing engaging rack bars in the well.

Elevators have been contrived automatically controlled by switch mechanisms on the landings; and in connection with the electric motor safety devices are used to break the motor circuit and thus stop the car the moment the elevator door is opened; and there are devices to break the circuit and stop the car at once, should an obstruction, the foot for instance, be accidentally thrust out into the path of the car frame.

Columns of water and of air have been so arranged that should the car fall the fall will be broken by the water or air cushion made to yield gradually to the pressure. So many safety devices have been invented that there is now no excuse for accidents. They result by a criminal neglect of builders or engineers to provide themselves with such devices, or by a most ignorant or careless management and operation of simple actuating mechanisms.

Between 1880 and 1890 there was great activity in the invention of what is known as store service conveyors. One of the earliest forms, and one which had been partly selected from other arts, was to suspend from a rigid frame work connected to the floor, roof, or side of the building, a long platform in the direction through the building it was desired the road to run, giving this platform a slight inclination. On this platform were placed tracks, and from the tracks were suspended trucks, baskets, or other merchandise receptacles, having wheels resting on and adapted to roll on the tracks. Double or single tracks could be provided as desired. The cars ran on these tracks by gravity, and considerable ingenuity was displayed in the feature alone of providing the out-going and returning inclined tracks; in hand straps and levers for raising and lowering the carriage, part or all of it, to or from the tracks, and in buffers to break the force of the blow of the carriages when arriving at their stopping places.

Then about 1882-83 it was found by some inventors if moderately fine wires were stretched level, and as tight as possible, they would afford such little friction and resistance to light and nicely balanced wheels, that no inclination of the tracks was necessary, and that the carriages mounted on such wheels and tracks would run the entire length of a long building and turn corners not too sharp by a single initial push of the hand. In other arrangements a carrier is self-propelled by means of a coiled spring on the carrier, which begins its operation as soon as the carrier is given a start; and to meet the exhausted strength of such spring, coiled springs at different points on the line are arranged to engage and give the carrier an additional push. Before the carrier is stopped its action is such as to automatically rewind its spring.

A system of pneumatic transmission was invented, by which a carrier is caused to travel through a tube by the agency of an air current, created therein by an air compressor, blower, or similar device. The device is so arranged that the air current is caused to take either direction through the tube; and in some instances gravity may be used to a.s.sist a vacuum formed behind the carrier. The tube is controlled at each end by one or more sliding gates or valves, and the carrier is made to actuate the gates, and close the one behind it, so that the carrier may be discharged without permitting the escape of the air and consequent reduction of pressure.

An interesting invention has been made by James M. Dodge of Philadelphia in the line of conveyors, whereby pea coal and other quite heavy materials introduced by a hopper into a trough are subjected to a powerful air blast which pushes the material forward; and as the trough is provided with a series of frequently occurring slots or perforations open to the outer air and inclined opposite the direction of travel, the powerful current from the blower in escaping through such outlets tends to lift or buoy the material and carry it forward in the air current, thereby greatly reducing frictional contact and increasing the impelling operation. The inventor claims that with such an apparatus many tons of material per hour may be conveyed with a comparatively small working air pressure.

In order that a conveyor carriage may be automatically switched off at a certain place or station on the line, one mode adopted was to arrange at a gate or station a sort of pin or projection or other deflector to engage some recess or corresponding feature on the carriage, so as to arrest and turn the carriage in its new direction at that point. Another mode was the adoption of electro-magnets, which would operate at a certain place to arrest or divert the carriage; and in either case the carriage was so constructed that its engaging features would operate automatically only in conjunction with certain features at a particular place on the line.

Signals have been also adopted, in some cases operated by an electric current, by which the operator can determine whether or not the controlling devices have operated to stop the carrier at the desired place. By electric or mechanical means it is also provided that one or more loop branches may be connected with or disconnected from the main circuit.

The "lazy tongs" principle has been introduced, by which a long lazy-tongs is shot forth through a tube or box to carry forward the carriage; and the same principle is employed in fire-escapes to throw up a cage to a great height to a window or other point, which cage is lowered gently and safely by the same means to the ground. Buffers of all kinds have been devised to effect the stoppage of the carrier without injury thereto under the different degrees of force with which it is moved upon its way, to prevent rebounding, and to enable the carrier to be discharged with facility at the end of its route.

Among the early mechanical means of transporting the carriage was an endless cable moved continuously by an engine, and this adoption of cable principle in store service was co-eval with its adoption for running street cars. Also the system of switching the cars from the main line to a branch, and in different parts of a city, at the same time that all lines are receiving their motive power from the main line, corresponds to the manner of conveying cash to all parts of a building at the same time from many points.

To the great department store or monstrous building wherein, as we have said, the whole business of a town may be transacted, the a.s.semblage and conjoint use of elevators and conveyors seem to be actually necessary.

A very useful and important line of inventions consists in means for forming connections between rotary shafts and their pulleys and mechanisms to be operated thereby, by which such mechanism can be started or stopped at once, or their motion reversed or r.e.t.a.r.ded; or by which an actuating shaft may be automatically stopped. These means are known as _clutches_.

They are designed often to afford a yielding connection between the shaft and a machine which shall prevent excessive strain and wear upon starting of the shaft. They are also often provided with a spring connection, which, in the rotation of the shaft in either direction, will operate to relieve the strain upon the shaft, or shafts, and its driving motor. Safety clutches are numerous, by which the machine is quickly and automatically stopped by the action of electro-magnets should a workman or other obstruction be caught in the machinery.

Electric auxiliary mechanism has also been devised to start or stop the main machine slowly, and thus prevent injury to small or delicate parts of complicated machines, like printing presses for instance. Clutches are arranged sometimes in the form of weights, resembling the action of the weights in steam governors, whereby centrifugal action is relied upon for swinging the weights outward to effect a clutching and coupling of the shaft, or other mechanism, so that two lines of shafting are coupled, or the machine started, or speeded, at a certain time during the operation. In order to avoid the great mischief arising sometimes from undue strain upon and the breaking of a shaft, a weak coupling composed of a link is sometimes employed between the shaft and the driven machine, whereby, should the force become suddenly too great, the link of weaker metal is broken, and the connection between the shaft thereby destroyed and the machine stopped.

To this cla.s.s of inventions, as well as to many others, the phrase, "labour-saving", is applied as a descriptive term, and as it is a correct one in most instances, since they save the labour of many human hands, they are regarded by many as detrimental to a great extent, as they result in throwing out of employment a large number of persons.

This derangement does sometimes occur, but the curtailment of the number of labourers is but temporary after all.

The increased production of materials, resulting from cheaper and better processes, and from the reduced cost of handling them, necessitates the employment of a larger number of persons to take care of, in many ways, the greater output caused by the increased demand; the new machinery demands the labour of additional numbers in its manufacture; the increase in the size and heights of buildings involves new modes of construction and a greater number of artisans in their erection; new forms of industry springing from every practical invention which produces a new product or results in a new mode of operation, complicates the systems of labour, and creates a demand for a large number of employers and employees in new fields. Hence, it is only necessary to resort to comparative, statistics (too extensive to cite here) to show that the number of unemployed people in proportion to the populations, is less in the present age than in any previous one. In this sense, therefore, inventions should be cla.s.sed as labour-_increasing_ devices.

CHAPTER XI.

HYDRAULICS.

The science of Hydraulics appears to be as old as the thirst of man.

When prehistoric men had only stone implements, with which to do their work, they built aqueducts, reservoirs and deep wells which rival in extent many great similar works that are the boast of their modern descendants. Modern inventors have also produced with a flourish nice instrumentalities for raising water, agencies which are covered with the moss of untold centuries in China.

It was more than an ancient observation that came down to Pliny's time for record, that water would rise to a level with its source. The observation, however, was put into practical use in his time and long before without a knowledge of its philosophical cause.

Nothing in Egyptian sculpture portraying the arts in vogue around the cradle of the human race is older than the long lever rocking upon a cleft stick, one arm of the lever carrying a bracket and the other arm used to raise a bucket from a well. Forty centuries and more have not rendered this device obsolete.

Among other machines of the Egyptians, the Carthaginians, the Greeks, and the Romans for raising water was the _tympanum_, a drum-shape wheel divided into radial part.i.tions, chambers, or pockets, which were open to a short depth on the periphery of the wheel, and inclined toward the axis, and which was driven by animal or manual power. These pockets scooped up the water from the stream or pond in which the wheel was located as the wheel revolved, and directed it toward the axis of the wheel, where it ran out into troughs, pipes, or gutters. The _Noria_, a chain of pots, and the screw of Archimedes were other forms of ancient pumps. The bucket pumps with some modifications are known in modern times as scoop wheels, and have been used extensively in the drainage of lands, especially by the Dutch, who at first drove them by windmills and later by steam.

The division of water-wheels into overshot, undershot and breast wheels is not a modern system.

In the _Pneumatics of Hero_, which compilation of inventions appeared in 225 B. C., seventy-nine ill.u.s.trations are given and described of simple machines, between sixty and seventy of which are hydraulic devices.

Among these, are siphon pumps, the force pump of Ctesibius, a "fire-pump," having two cylinders, and two pistons, valves, and levers.

We have in a previous chapter referred to Hero's steam engine. The fact that a vacuum may be created in a pump into which water will rise by atmospheric pressure appears to have been availed of but not explained or understood.

The employment of the rope, pulley and windla.s.s to raise water was known to Hero and his countrymen as well as by the Chinese before them. The chain pump and other pumps of simple form have only been improved since Hero's day in matters of detail. The screw of Archimedes has been extended in application as a carrier of water, and converted into a conveyor of many other materials.

Thus, aqueducts, reservoirs, water-wheels (used for grinding grain), simple forms of pumps, fountains, hydraulic organs, and a few other hydraulic devices, were known to ancient peoples, but their limited knowledge of the laws of pneumatics and their little mechanical skill prevented much general progress or extensive general use of such inventions.

It is said that Frontinus, a Roman Consul, and inspector of public fountains and aqueducts in the reigns of Nerva and Trajan, and who wrote a book, _De Aquaeductibus Urbis Romae Commentarius_, describing the great aqueducts of Rome, was the first and the last of the ancients to attempt a scientific investigation of the motions of liquids.

In 1593 Serviere, a Frenchman, born in Lyons, invented the rotary pump.

In this the pistons consisted of two cog wheels, their leaves intermeshing, and rotated in an elliptical shaped chamber. The water entered the chamber from a lower pipe, and the action of the wheels was such as to carry the water around the chamber and force it out through an opposite upper pipe. Subsequent changes involved the rotating of the cylinder instead of the wheels and many modifications in the form of the wheels. The same principle was subsequently adopted in rotary steam engines.

In 1586, a few years before this invention of Serviere, Stevinus, the great engineer of the dikes of Holland, wrote learnedly on the _Principles of Statics and Hydrostatics_, and Whewell states that his treatment of the subject embraces most of the elementary science of hydraulics and hydrostatics of the present day. This was followed by the investigations and treatises of Galileo, his pupil Torricelli, who discovered the law of air pressure, the great French genius, Pascal, and Sir Isaac Newton, in the 17th century; and Daniel Bernoulli, d'Alembert, Euler, the great German mathematician and inventor of the centrifugal pump, the Abbe Bossut, Venturi, Eylewein, and others in the 18th century.

It was not until the 17th and 18th centuries that mankind departed much from the practice of supplying their towns and cities with water from distant springs, rivers and lakes, by pipes and aqueducts, and resorted to water distribution systems from towers and elevated reservoirs.

Certain cities in Germany and France were the first to do this, followed in the 18th century by England. This seems strange, as to England, as in 1582 one Peter Maurice, a Dutch engineer, erected at London, on the old arched bridge across the Thames, a series of forcing pumps worked by undershot wheels placed in the current of the river, by which he forced a supply of water to the uppermost rooms of lofty buildings adjacent to the bridge. Before the inventions of Newcomen and Watt in the latter part of the 18th century of steam pumps, the lift and force pumps were operated by wheels in currents, by horses, and sometimes by the force of currents of common sewers.

When the waters of rivers adjacent to towns and cities thus began to be pumped for drinking purposes, _strainers_ and _filters_ of various kinds were invented of necessity. The first ones of which there is any printed record made their appearance in 1776.

After the principles of hydraulics had thus been reviewed and discussed by the philosophers of the 17th and 18th centuries and applied, to the extent indicated, further application of them was made, and especially for the propelling of vessels. In 1718 La Hire revived and improved the double-acting pump of Ctesibius, but to what extent he put it into use does not appear. However, it was the double-acting pump having two chambers and two valves, and in which the piston acted to throw the water out at each stroke.

In 1730 Dr. John Allen of England designed a vessel having a tunnel or pipe open at the stern thereof through which water was to be pumped into the air or sea--the reaction thus occasioned driving the vessel forward.

He put such a vessel at work in a ca.n.a.l, working the pumps by manual labor, and suggested the employment of a steam engine. A vessel of this kind was patented by David Ramsey of England in 1738. Rumsey of America in 1782 also invented a similar vessel, built one 50 feet long, and ran it experimentally on the Potomac river. Dr. Franklin also planned a boat of this kind in 1785 and ill.u.s.trated the same by sketches. His plan has since been tried on the Scheldt, but two turbines were subst.i.tuted for his simple force pump. Further mention will be made later on of a few more elaborate inventions of this kind.

It also having been discovered that the fall of a column of water in a tube would cause a portion of it to rise higher than its source by reason of the force of momentum, a machine was devised by which successive impulses of this force were used, in combination with atmospheric pressure, to raise a portion of the water at each impulse.

This was the well-known _ram_, and the first inventor of such a machine was John Whitehurst of Cheapside, England, who constructed one in 1772.

From a reservoir, spring, or cistern of water, the water was discharged downward into a long pipe of small diameter, and from thence into a shorter pipe governed by a stop-c.o.c.k. On the opening of the stop-c.o.c.k the water was given a quick momentum, and on closing the c.o.c.k water was forced by the continuing momentum through another pipe into an air chamber. A valve in the latter-mentioned pipe opened into the air chamber. The air pressure served to overcome the momentum and to close the chamber and at the same time forced the water received into the air chamber up an adjacent pipe. Another impulse was obtained and another injection of water into the chamber by again opening the stop-c.o.c.k, and thus by successive impulses water was forced into the chamber and pressed by the air up through the discharge pipe and thence through a building or other receptacle. But the fact that the stop-valve had to be opened and closed by hand to obtain the desired number of lifts rendered the machine ineffective.

In 1796 Montgolfier, a Frenchman and one of the inventors of the balloon, subst.i.tuted for the stop-c.o.c.k of the Whitehurst machine a loose impulse valve in the waste pipe, whereby the valve was raised by the rush of the water, made to set itself, check the outflow and turn the current into the air chamber. This simple alteration changed the character of the machine entirely, rendered it automatic in action and converted it into a highly successful water-raising machine. For this invention Montgolfier obtained a Gold Medal from the French Exposition of 1802. Where a head can be had from four to six feet, water can be raised to the height of 30 feet. Bodies of water greater in amount than is desired to be raised can thus be utilised, and this simple machine has come into very extensive use during the present century.

Allusion was made in the last chapter to the powerful hydraulic press of Joseph Bramah invented in 1795-1800, its practical introduction in this century and improvements therein of others. After the great improvements in the steam engine made by Watt, water, steam and air pressure joined their forces on the threshold of this century to lift and move the world, as it had never been moved before.

The strong hands of hydraulics are pumps. They are divided into cla.s.ses by names indicating their purpose and mode of operation, such as single, double-acting, lift or force, reciprocating or rotary, etc.

Knight, in his celebrated _Mechanical Dictionary_, enumerates 100 differently constructed pumps connected with the various arts. In a broader enumeration, under the head of _Hydraulic Engineering and Engineering Devices_, he gives a list of over 600 species. The number has since increased. About nine-tenths of these contrivances have been invented during the 19th century, although the philosophical principles of the operation of most of them had been previously discovered.

The important epochs in the invention of pumps, ending with the 18th century, were thus the single-acting pump of Ctesibius, 225 B. C., the double-acting of La Hire in 1718, the hydraulic ram of Whitehurst, 1772, and the hydraulic press of Bramah of 1795-1802.

Bramah's press ill.u.s.trates how the theories of one age often lie dormant, but if true become the practices of a succeeding age. Pascal, 150 years before Bramah's time, had written this seeming hydraulic paradox: "If a vessel closed on all sides has two openings, the one a hundred times as large as the other, and if each be supplied with a piston which fits it exactly, then a man pushing the small piston will equilibrate that of 100 men pushing the piston which is 100 times as large, and will overcome the other 99." This is the law of the hydraulic press, that intensity of pressure is everywhere the same.

The next important epoch was the invention of Forneyron in 1823, of the water-wheel known as the Turbine and also as the Vortex Wheel. If we will return a moment to the little steam engine of the ancient Hero of Alexandria, called the Eolipile, it will be remembered that the steam admitted into a pivoted vessel and out of it through little opposite pipes, having bent exits turned in contrary directions, caused the vessel to rotate by reason of the reaction of the steam against the pipes. In what is called Barker's mill, brought out in the 18th century, substantially the same form of engine is seen with water subst.i.tuted for the steam.