Chapter III: Part 3

The Romans are supposed to have had some knowledge of the power of steam. Among amusing anecdotes, showing the knowledge the ancients had of steam, it is told that Anthemius, the architect of Saint Sophia, lived next door to Zeno. There existed a feud between them, and to annoy his neighbour, Anthemius had some boilers placed in his house containing water, with a flexible tube which he could pass through a hole in the wall under the floor of Zeno's dwelling; he then lit a fire, which soon caused steam to pass through the tube in such a quantity as to make the floors to heave as if by an earthquake. But to return. We next come to Blasco de Garay (A.D. 1543), who proposed to propel a ship by the power of steam. So much cold water seems to have been thrown on his engine, that it must have condensed all his steam, as little notice is taken of it except that he got no encouragement. We find that it has also been used by some of the ancients in connection with their deities. Rusterich, one of the Teutonic gods, which was found in an excavation, proves how the priests deceived the people. The head of this one was made of metal and contained a pot of water. The mouth and another hole in the forehead being stopped by wooden plugs, a fire of charcoal was lighted under this pot of water, and at length the steam drove out the plugs with a great noise, and the god was shrouded in a mist of steam which concealed him from his astonished worshippers.

In 1629, Giovanni Branca of Loretto in Italy, an engineer and architect, proposed to work mills and other machinery by steam blowing against vanes, much in the same way as water does in turning a wheel. The waste of steam in such a plan is so obvious, that it is not to be wondered at that it did not produce any great results, as we all know that the moment we let steam out of his case, the case is all up with him, and he dies a natural death. He is a most delicate yet powerful agent, and requires to be kept warm in all weathers--this fact does not seem to have struck Mons. Branca when he let him out of his boiler.

The next person we come to, and perhaps the first of any note, is the Marquis of Worcester in 1663 (died 1667). He was a man who seems, as far as history tells us, to have taken a great interest in furthering the advancement of steam. He was not contented with one invention, but published a book entitled "A Century of Inventions," and in this work he describes a means of raising water by the pressure of steam. The Marquis appears to have been a politician as well as an inventor, as we find he was engaged on the side of the Royalists in the Civil Wars of the Revolution, lost his fortune and went to Ireland, where he was imprisoned. Escaping to France, from thence he returned to London as a secret agent of Charles II., but was detected and imprisoned in the Tower, where he remained till the Restoration, when he was set at liberty. One day, while in prison, he observed the lid of the pot in which his dinner was being prepared lifted up by the vapour of the water boiling inside. Reflecting on this, he turned his mind to the matter, and thought that this vapour, if rightly applied, might be made a useful moving power. He thus describes his invention in his 68th Article: "I have contrived an admirable way to drive up water by fire, not by drawing or sucking it upwards, thirty-two feet. But this way hath no bounds, if the vessels be strong enough." He then goes on to say, that "having a way to make his vessels, so that they are strengthened by the force within, I have seen the water run like a constant stream forty feet high. One vessel rarified by fire driveth forty of cold water, and one being consumed, another begins to force, and refill with cold water, and so on successively, the fire being kept constant. The engineman having only to turn two cocks, so as to connect the steam with the one or the other vessel."

In this engine, if it can be called an engine, we see that the Marquis had a good idea of the power of steam, but he had none, you will observe, as to the action of the condensation which would immediately take place when the steam from the boiler was brought into contact with the cold water to be raised. Therefore this plan would be most expensive, on account of the great loss of steam by condensation. It was, however, quite able to produce the effect, though only equal to raising 20 cubic feet of water, or 1250 lbs., one foot high by one pound of coal, or about the two-hundredth part of the effect of a good steam-engine. After this, of course, it proved of no avail; but still we may say that the Marquis of Worcester was among the first who tried to make, and did do so, steam a moving power.

Our next is Denys Papin (died 1710), a native of Blois, in France, who was mathematical professor at Marpurg. To him is due the discovery of one of the qualities of steam--its condensation, so as to produce a vacuum, to the proper management of which our modern engines owe much of their efficacy. Papin seems to have been the first who conserved the idea of the cylinder and piston, which he made to act on atmospheric principles--that is to say, he took a cylinder with a piston moving up and down in it, and found that by removing the air from under the piston in the cylinder, that the pressure of the atmosphere would drive it down to the bottom of the cylinder: this he performed by admitting steam, and then condensing it rapidly, so causing the required vacuum. The pressure of the atmosphere is as near as may be 16 lbs. on every square inch of surface on the globe: this is obviously the weight of the columns of air extending from that square inch of surface upwards to the top of the atmosphere. This force is thus measured: Take a glass tube 32 inches long, open at one end and closed at the other; provide also a basin full of mercury; let the tube be filled with mercury and inverted into the basin. The mercury will then fall in the tube, till it gets to that height which the atmosphere will sustain. This is nothing more than the barometer used in all our houses. If the action of the tube be equal to a square inch, the weight of the column of mercury in the tube would be exactly equal to the weight of the atmosphere on each square inch of surface. Thus Papin discovered a great step in the steam-engine, though it was not much acted on for some years; he was also the first who proposed to drive ships with paddles worked by steam.

We now come to Thomas Savory, who got a patent in 1698 for a method of condensing steam to form a vacuum. Savory describes his discovery in this way:--Having drank a flask of wine at a tavern, he flung the empty flask on the fire, and then called for a basin of water to wash his hands. A little wine remained in the flask, which of course soon boiled, and it occurred to him to try what effect would be produced by putting the mouth of the flask into the cold water. He did this, and in a moment the cold water rushed up and filled the flask, this being caused by the steam being condensed and leaving a vacuum, which Nature abhors, and rather than permit this the water rushed up and took the place formerly occupied by the now condensed steam. We see by this in how simple a way great ends are produced, and in the age in which this happened, the result may be indeed be said to have produced a great end. The engine of Savory was used for some years as a machine to raise water. The principle of his engine was just as I have stated, and consisted of two cases and other various parts, and this engine possessed advantages over that of the Marquis of Worcester in sucking up the water as well as forcing.

Savory's engine consisted of two steam vessels connected to a boiler by tubes; a suction pipe, or that pipe which leads from a pump of the present day to the well, and communicating with each of the steam vessels by valves opening upwards; a pipe going from these steam vessels to any required height to which the water is to be raised. The steam vessels were connected to this pipe by other valves, also opening upwards, and by pipes. Over the steam vessels was placed a cistern, which was kept filled with _cold_ water. From this proceeded a pipe with a stopcock. This cistern was termed the condensing cistern, and the pipe could be brought over each steam vessel alternately from the boiler. Now, suppose the tubes to be filled with common air, and the regulator placed so that one tube and the boiler are made to communicate, and the other tube and the boiler closed, steam will fill one of the steam vessels through one tube; at first it will condense quickly, but erelong the heat of the steam will impart its heat to the metal of the vessel, and it will cease to condense. Mixed with the heated air, it will acquire a greater force than the air outside the valve, which it will force open, and drive out the mixture of air and steam, till all the air will have passed from the vessel, and nothing but the vapour of water remain. This done, a cock is opened, and the water from the cistern is allowed to flow over the outside of the steam vessel, first having stopped the further supply of steam from it; this produced the immediate condensation of the steam contained in it, by the temperature being brought down again by the cold water, and the condensation thus produced caused a vacuum inside the vessel. The valve will then be kept closed by the atmosphere outside, and the pressure of the air on the surface of the water in the well or reservoir will open another valve, force the water up the pipe, till, after one or two exhaustions--if I may so term it--it will at last reach the second vessel. Thus far the atmosphere has done all the work, but at last the water fills the vessel, and then comes the forcing point. Now the power of the steam itself is used to drive the water up the pipe. The steam is again let into the vessel, now filled in whole, or at least in great part, with water; at first it will, as before, condense rapidly, but soon the surface of the water will get heated, and as hot water is lighter than cold, it will keep on the surface, and the pressure of the steam from the boiler will drive all the water from the vessel up the pipe. When it is empty the cock is again opened, and the steam, which the vessel by this time only contains, is again condensed, and the same process which I have just described is again commenced and carried out, thus making Savory's engine a complete pump by the aid of the vapour of water as raised by fire.

Savory had the honour of showing this engine to His Majesty William III. at Hampton Court Palace, and to the Royal Society. He proposed the following uses, which perhaps may as well be mentioned, as they show how little was then known of the real value of the power of steam:--1. To raise water to drive mill-wheels--fancy erecting a steam engine now, of say fifty horse-power, to raise water to turn a wheel of say thirty; 2. To supply palaces and houses with water; 3. Towns with water; 4. Draining marshes; 5. Ships; 6. Draining mines. There is one more thing I may mention as curious, that though the steam he used must have been of a high pressure, he did not use a safety-valve, though it had been invented about the year 1681 by Papin. The consumption of fuel was enormous in Savory's engine, as may easily be perceived from the great loss of steam by condensation. Nevertheless, it was on the whole a good and a workable engine, as we find the following said of it by Mr. Farey:--"When comparison is made between Captain Savory's engine and those of his predecessors, the result will be favourable to him as an inventor and practical engineer. All the details of his invention are made out in a masterly style, so as to make it a real workable engine. His predecessors, the Marquis of Worcester, Sir S. Morland, Papin, and others, only produced outlines which required to be filled up to make them workable."

I must not detain you much longer before I proceed to the great Watt, but I will just name Newcomen, who invented an engine with a cylinder, and introduced a beam, to the other end of which he fixed a pump rod like a common or garden pump. He made the weight of the pump and beam to lift the piston, and then let the steam enter below the piston and condensed it by a jet of water, thus causing a vacuum, when the pressure of the atmosphere drove the piston from the top to the bottom of the cylinder and lifted the pump rods in the usual way. There were various cocks to be opened and shut in the working of this engine for the right admission of steam and water at the required moments, a task which was performed by boys who were termed cock-boys. I will now mention an instance which, though in practice not to be imitated, yet was one of those happy accidents which sometimes turn out for the best. One of these boys, like many, more fond of play than work, got tired of turning these cocks day by day, and conceived the idea of making the engine do it for itself. This idle boy--we will not call him good-for-nothing, as he proved good for a great deal in one way--was named Humphrey Potter, and one day he fixed strings to the beam, which opened and shut the valves, and so allowed him to play, little thinking this was one of the greatest boons he could possibly have bestowed on the world at large, for by so doing he rendered the steam-engine a self-acting machine.

We now come to a period which was destined to advance the cause of steam to a far greater extent--in fact, the time which rendered the steam-engine the useful and valuable machine it now is. This is the time of James Watt. This great man, be it said to the credit of Scotland, was born in Greenock, on the Clyde, on the 19th January 1736. His grandfather was a farmer in Aberdeenshire, and was killed in one of the battles of Montrose. His father was a teacher of mathematics, and was latterly chief magistrate of Greenock. James Watt, the celebrated man of whom I now speak, was a very delicate boy, so much so, that he had to leave school on account of his health, and was allowed to amuse himself as he liked. This he did in a scientific way, however, as an aunt of his said to him one day: "Do you know what you have been doing? You have taken off and put on the lid of the teapot repeatedly; you have been holding spoons and saucers over the steam, and trying to catch the drops of water formed on them by it. Is it not a shame so to waste your time?" Mrs. Muirhead, his aunt, was little aware that this was the first experiment in the way which afterwards immortalised her nephew.

In 1775 Watt was sent to London to a mathematical instrument maker, but could not stay on account of his health, and soon afterwards came back to Glasgow. He then got rooms in the College, and was made mathematical instrument maker to the University, and he afterwards opened a shop in the town. He was but twenty-one years of age when he was appointed to this post in the College, and his shop became the lounge of the clever and the scientific. The first time that his attention was directed to the agency of steam as a power was in 1734, when a friend of his, Mr. Robinson, who had some idea of steam carriages, consulted him on the subject,--little is said of this, however. In 1762 Watt tried some experiments on high-pressure steam, and made a model to show how motion could be obtained from that power; but did not pursue his experiments on account of the supposed danger of such pressure. He next had a model of Newcomen's engine, which would not work well, sent him to repair. Watt soon found out its faults, and made it work as it should do. This did not satisfy him, and setting his active mind to work, he found in the model that the steam which raised the piston had of course to be got rid of. This, as a natural consequence, caused great loss of heat, as the cylinder had to be cooled so as to condense the steam; and this led him at last, after various plans, to adopt a separate vessel to condense this steam. Of course, if you wish to save fuel, it is necessary that the steam should enter a heated cylinder or other vessel, or else all the steam is lost,--or in other words, condensed,--that enters it, until it has from its own heat imparted so much to the cylinder as to raise it to its own temperature, when it will no longer condense, and not till then does it begin to exert its elastic power to produce motion. This was the great object gained by James Watt, when, after various experiments, he gave up the idea altogether of condensing steam in its own or working cylinder, and then made use of a separate vessel, now called the condenser.

The weight of steam is about 1800 times less than water. I may here perhaps mention also that water will boil at 100 degrees Fahr. in vacuo, whereas in atmosphere it takes 212 degrees to boil. There is also a thing perhaps worth knowing to all who wish to get the most stock out of bones, &c., that if they are boiled in a closed vessel, that is to say, under a pressure of steam, a very large increase in quantity of the stock will be produced, because the heat is increased. A cubic inch of water, evaporated under _ordinary_ atmospheric pressure, will be converted into a cubic foot of steam; and a cubic inch of water, evaporated as above, gives a mechanical force equal to raising about a ton a foot high.

The next great improvement of Watt, in addition to the condenser, is the air-pump, the use and absolute necessity for which you will understand when I explain its action. Watt first used it for his atmospheric engine. The piston of this engine was kept tight by a flow of oil and water on the top, which tended to make the whole a troublesome and bad-working machine. The cold atmosphere, as the piston went down, of course followed it and cooled the cylinder. On the piston again rising, some steam would of course be condensed and cause waste. If the engine-room could be kept at the heat of boiling water, this would not have been the case, but the engineman who could live in this heat would also require to be invented, and so this had to be given up. Watt's next and most important step was the one which brings us to talk of the steam-engine as it now is in the present day. This important step was the idea, of making the steam draw down the piston, as well as help to drive it up; in the first engines it was raised by the beam, and steam used only to cause a vacuum, so as to let the air drive it down. All before this had been merely steps in advance, like those of children, who must walk before they can run; so was it with the steam-engine. It was uphill work for many years, and the top of the hill cannot be said to have been readied till Watt worked out this grand idea. The first engine could only be called atmospheric; now it was destined to become in reality a steam-engine. Time would fail were I to attempt to go into any details of all the experiments through which Watt toiled to bring his ideas to perfection--enough to say that he did so; and I trust you will be able, through the description I will endeavour to give, to understand how well his labour was bestowed, and how beautiful the result has proved for the benefit of the world at large. In 1773, Watt removed to Soho, near Birmingham, where a part of the works was allotted to him to erect the machinery necessary to carry out his inventions on a grand scale.

We must now proceed to some of the useful points of the engine, all I have before mentioned simply relating to the inventors and improvers; but having brought it so far, I may now, I think, proceed further. The first use of the steam-engine was simply to raise water from mines, and for long it was thought it could be used for nothing else; so much so, that it was at one time used to raise water to turn wheels and thus produce motion. One of its first uses after it became a really useful machine was to propel ships, though many a weary hour was spent to bring it to this point. There is a very pretty monument on the Clyde, dedicated to Mr. Bell, who I believe was the first person who successfully brought steamers to work on its waters. The first who used steam for ships was Mr. James Taylor, in conjunction with Mr. Miller of Dalswinton. The danger of the fire-ship took such hold on people's minds that it was with great toil and difficulty they were persuaded to venture on the face of the waters in such dangerous and unseamanlike craft. But go to Glasgow Bridge any day, and you will see how time has overcome fear and prejudice, for our ocean is covered with steamers of all sizes. It is not many years ago since it was said that steamers could never reach America; this has given way to proof, and even Australia has been reached by steam. I know of a steamer building which could carry the whole population of this place and not be full; she is 680 feet or 226 yards long, and a large vessel would hang like a boat alongside her.

The first attempt at giving motion by steam to ships was of course only in one way--by a ratchet at the end of a beam, at one moment driving and the next standing still. This was on account of the engine being only in power one half of the stroke; but by the double-acting engine being introduced, and the steam acting both ways, it became at last a steady mover (without the aid of two or three cylinders, as in the first engines, one to take up the other as the power was given off), by a ratchet on the end of a beam or else a chain. This acted on the shaft which moved the paddles. It is to Watt that we are indebted for the crank and direct action, so as to give a circular motion to the wheels.

We find in 1752 a Mr. Champion of Bristol applied the atmospheric engine to raise water to drive a number of wheels for working machinery in a brasswork, in other words, a foundry. Also, in Colebrokedale, steam-engines were used to raise water that had passed over the wheel, so as to save water. All these plans have, however, now passed by, like the water over the wheel, and we now have the engine the prime mover--the double action of the steam on the piston, this acting on the sway beam, and the beam on the crank, which, by the assistance of the fly-wheel on land or fixed engines, gives a uniform motion to the machine. All these have now enabled us to apply the engine as our grand moving power. One great and important point in the engine is the governor, and the first modes of changing the steam from the top to the bottom of the cylinder were cumbrous, till the excentric wheel was devised.

Boilers also have to be attended to--these were at first rude and now would be useless. They were unprovided with valves, gauge-cocks, or any other safety, all of which are now so well understood that nothing but carelessness can cause a blow-up. One of the greatest causes of danger is that of letting there be too little water in the boiler, and thus allowing it to get red-hot, when, if you let in water, such a volume of steam is generated that no valve will let it escape fast enough. Force or feed pumps are also required to keep the water in the boiler at a proper height, which is ascertained by the gauge-cocks. Mercury gauges for low pressure act according to the pressure of the atmosphere; high-pressure boilers of course require a different construction, as the steam is greater in pressure than the air.

Having got so far in my subject, I think before concluding I must devote a short time in showing the first steps of the locomotive; the more so, as I am speaking to those who are so largely engaged in the daily working of that now beautifully perfect machine. Various and for a time unsuccessful experiments were made to bring out a machinery or travelling engine, as it was first called. A patent was taken by a Mr. Trevethick for a locomotive to run on common roads, and to a certain extent it did work. An amusing anecdote is told of it. In coming up to a toll-gate, the gatekeeper, almost frightened out of his seven senses, opened the gate wide for the monster, as he thought, and on being asked what was to pay, said "Na-na-na-na!" "What have we got to pay?" was again asked. "No-noth-nothing to pay, my dear Mr. Devil; do drive on as fast as you can!" This, one of the first steam carriages, reached London in safety, and was exhibited in the square where the large station of the London and North-Western Railway now stands. Sir Humphrey Davy took great interest in it, and, in writing to a friend, said: "I shall hope soon to see English roads the haunts of Captain Trevethick's dragons." The badness of roads, however, prevented its coming into general use.

Trevethick in 1804 constructed a locomotive for the Merthyr and Tydvil Rail in South Wales, which succeeded in drawing ten tons at five miles an hour. The boiler was of cast-iron, with a one-cylinder engine, spur gear and a fly-wheel on one side. He sent the waste steam into the chimney, and by this means was very nearly arriving at the blast-pipe, afterwards the great and important discovery of George Stephenson. The jumping motion on the bad roads, however, caused it constantly to be dismounted, and it was given up as a practical failure, being sent to work a large pump at a mine. Trevethick was satisfied with a few experiments, and then gave it up for what he thought more profitable speculations, and no further advances were made in locomotives for some years. An imaginary difficulty seems to have been among the obstacles to its progress. This was the supposition that if a heavy weight were to be drawn, the grip or bite of the wheels would not be sufficient, but that they would turn round and leave the engines stationary, hence Trevethick made his wheels with cogs, which of course tended to cause great jolts, as well as being destructive to the cast-iron rails.

A Mr. Blenkinsop of Leeds patented in 1811 a locomotive with a racked or toothed rail. It was supported on four wheels, but they did not drive the engine; its two cylinders were connected to one wheel behind, which was toothed and worked in the cog-rail, and so drove the engine. It began running on Middleton Coal Rail to Leeds, three and a quarter miles, on the 12th August 1812, and continued a great curiosity to strangers for some years. In 1816 the Grand Duke Nicholas of Russia saw this engine working with great interest and expressions of no slight admiration. An engine then took thirty coal-waggons at three and a quarter miles in an hour.

We next come to Messrs. Chapman of Newcastle, who in 1812 tried to overcome the supposed want of adhesion by a chain fixed at the ends of the line and wound round a grooved drum driven by the engine. It was tried on the Heaton Rail near Newcastle, but was found to be so clumsy that it was soon abandoned. The next was a remarkable contrivance--a mechanical traveller to go on legs. It never got beyond its experimental state, and unfortunately blew up, killing several people. All these plans show how lively an interest was then being taken in endeavouring to bring out a good working locomotive. Mr. Blackett, however, persevered hard to perfect a railway system, and to work it by locomotives. The Wylam waggon-way, one of the oldest in the North, was made of wooden rails down to 1807, and went to the shipping-place for coals on the Tyne. Each chaldron-waggon was originally drawn by a horse with a man in charge, only making two journeys in the one day and three on the following, the man being allowed sevenpence for each journey. This primitive railway passed before the cottage where George Stephenson was born, and was consequently one of the first sights his infant eyes beheld; and little did his parents think what their child was destined to work out in his day for the advancement of railways. Mr. Blackett took up the wood and laid an iron plate-way in 1808, and in 1812 he ordered an engine on Trevetbick's principle. It was a very awkward one, had only one cylinder of six inches diameter, with a fly-wheel; the boiler was cast-iron, and was described by the man who had charge of it as having lots of pumps, cog-wheels, and plugs. It was placed on a wooden frame with four wheels, and had a barrel of water on another carriage to serve as a tender. It was at last got on the road, but would not move an inch, and her driver says:--"She flew all to pieces, and it was the biggest wonder we were not all blown up." Mr. Blackett persevered, and had another engine, which did its work much better, though it often broke down, till at length the workmen declared it a perfect plague. A good story is told of this engine by a traveller, who, not knowing of its existence, said, after an encounter with the Newcastle monster working its great piston, like a huge arm, up and down, and throwing out smoke and fire, that he had just "encountered a terrible deevil on the Hight Street road."

We now come to George Stephenson, who did for the locomotive what Watt did for our other steam-engines. His first engine had two vertical cylinders of eight inches diameter and two-feet stroke, working by cross-heads; the power was given off by spur-wheels; it had no springs, consequently it jolted very much on the then bad railways; the wheels were all smooth, as Stephenson was sure the adhesion would be sufficient. It began work on the 25th July 1814, went up a gradient of one in 450, and took eight waggons with 30 tons at four miles an hour. It was by far the most successful engine that had yet been made. The next and most valuable improvement of Stephenson was the blast-pipe--by its means the slow combustion of the fire was at once overcome, and steam obtained to any amount. This pipe was the result of careful observation and great thought. His next engine had horizontal connecting rods, and was the type of the present perfect machine. This truly great man did not rest here, but time would fail, as well as your patience, if I were to proceed further. Enough to say, that he afterwards established a manufactory at Newcastle, and time has shown the result and benefit it has proved to the whole world at large. A short time before the Liverpool and Manchester Railway was opened, Stephenson was laughed at because he said he thought he could go thirty miles an hour, and was urged before the House of Commons not to say so, as he might be thought to be mad. This I have from person who knew the circumstances. Nevertheless, at the trial, I believe the "Rocket" did go at the rate of thirty miles an hour, to the not small astonishment of the world, and especially to the unbelievers in steam as a land agent. The stipulation made was that trains were to be conveyed at the rate of twelve miles an hour.

In our present perfect engines, the coke or fuel consumed per mile is about 18 lbs. with a train of 100 tons gross weight, carrying 250 passengers. A first-class carriage weighs 6 tons 10 cwts.; a second-class, 5 tons 10 cwts., each with passengers; a Pullman car weighs about 30 tons. Our steamers consume 5 lbs. of coal per horse-power in one hour. And last, not least, one of the greatest improvements we have had in steam propulsion is the screw. Again, I may also name the great advantage derived from steam by our farmers in thrashing out grain. The engines principally used in farm-work are what are termed high-pressure, or of the same class as the locomotive. The great saving in cost in the first place, the simplicity and ease of action in the second, and the small quantity of water required to keep them in action, are all reasons why they should be preferred. The danger in the one, that is, the high-pressure, over the condenser, is very small, and all that is required is common care to guard against accidents. Steam being a steady power, is much to be preferred to water, as by its constant and uniform action the tear and wear of machinery is much diminished, and of course proportionate saving made in keeping up the mill or any other machinery.

Having now, to the best of my power, so far as a single lecture will permit, brought the steam-engine from 120 B.C. to the present time, it only remains for me to say, that it shows how actively the mind of man has been permitted to work to bring it to perfection by the direction of an all-wise Providence, "who knows our necessities before we ask, and our ignorance in asking." A traveller by rail sees but little of the vast and difficult character of the works over which he is carried with such ease and comfort. Time is his great object. No age of the world has conquered such difficulties as our engineers have had to deal with, and the result is now before the eye of every thinking traveller. Our engineers were at first self-taught, and many a self-taught man has had reason to rejoice in the time he spent in his education. Of these men we have examples in Brindley, who was at first a labourer and afterwards a millwright; Telford was a stone-mason; Rennie a farmer's son apprenticed to a millwright; and George Stephenson was a brakesman at a colliery. Perseverance with genius, and a determination to overcome, made them the great men they were. That you may so persevere and strive is the earnest wish of him who has this evening had the great pleasure of giving you this lecture, and who feels so greatly obliged to you for the very patient hearing you have given him.

_ON ATTRACTION_.[B]

_Gravitation_.--Attraction, which may be illustrated by the effect a magnet has on a piece of iron, may be viewed generally as an influence which two bodies, say, exert on each other, under which, though at a distance, they tend to move towards each other till they come into contact. The force by which a body has weight, and, when free, falls to the ground, is of this nature; and it is called, from _gravis_, "heavy," the gravitating force of the earth, because it causes weight, and because, though emanating in a small degree from the falling body, it is mainly exerted by the earth itself. It is under the action of gravity that a pendulum oscillates: it is by that unseen influence it begins to sway alternately downward and upward as soon as it is moved to a side; and it is only because it is withheld by the rod that the ball or bob keeps traversing the arc of a circle and does not fall straight to the earth.

All material substances, however small, and however light, buoyant, and ethereal they may seem, are subject to this force: the tiniest speck in a sunbeam and the most volatile vapour, equally with the heaviest metal and the hugest block, the particles of bodies as well as the bodies themselves. The rising of a balloon in the air may seem an exception to this law; but it is not so; for the balloon rises, not because the particles of the gas with which it is inflated are not acted upon by the earth's attraction, but because the air outside being bulk for bulk heavier than the air inside, its particles press in below the balloon and buoy it up, until it reaches a stratum of the atmosphere where, the pressure being less, the air outside is no heavier than the air within--a fact which rather proves than disproves the universal action of gravitation; because the greater weight of the air in the lower strata of the atmosphere is due to the pressure of the air in those above, and the balloon ceases to ascend because it has reached a point where the air outside is the same weight as the air within, and the weight in both cases is caused by the attraction of the earth.

And not only is the force of attraction universal, it is the same for every particle; for though this may seem to be contradicted by the fact that some bodies fall faster to the ground than others, that fact is fully accounted for by the greater resistance which the air offers to the falling of lighter bodies than to the falling of heavier. A particles of bodies, and all bodies, tend to fall with the same velocity, and, in fact, all do; for though, for the reason just stated, a feather will take longer to reach the ground than an ounce of lead, an ounce of lead will fall as fast as a hundredweight. And that it is the resistance of the air, and not any diminution in the power of attraction, which causes the feather to lag behind, may be proved by experiment; for if you let a feather and a coin drop together from the top of the exhausted receiver of an air-pump, they will both be seen to descend at the same rate, and reach the bottom at the same instant; a fact which may be demonstrated more simply by placing the coin and feather free of each other in a paper cone, and letting the cone fall with its apex downwards, so as to break the air's resistance; or by suspending a piece of gold-leaf in a bottle, and letting the bottle drop--of course short of the ground--in which case the included leaf will be seen to have gone as fast and as far as the bottle.

It is to be especially noticed that attraction is no lopsided affair; that it is mutual; that, while the larger body attracts the less, the less also attracts and moves the larger in proportion; and that, indeed, every body and every particle attracts every other, far as well as near, to the utmost verge of the universe of matter. Under it the moon maintains its place with reference to the earth, the planets with reference to the sun, and the solar system with reference to the stellar. As for the moon, it maintains its orbit and revolves round the earth under the action of two forces, the one akin to that by which a ball is projected from the mouth of a cannon, and the other the attraction of the earth, which, by its constant and equal operation, bends its otherwise rectilineal track into a circular one, as we might show if we could only project a ball with such a force as exactly to balance the power of gravity, so that it would at no point in its course be drawn nearer the earth than at starting.

That the force we are considering pervades the solar system is demonstrable, for it is on the supposition of it and the laws it is known to obey that all the calculations of astronomy--and they never miscarry--are grounded; and it is by noticing disturbances in the otherwise regular movements of certain planets that astronomers have been led more than once to infer and discover the presence of some hitherto unknown body in the neighbourhood. It was actually thus the planet Neptune was discovered in 1846. Certain irregularities had been observed in the movements of Uranus, which could not be accounted for by the influence of any other bodies known to be near it; and these irregularities, being carefully watched and studied, gradually led more than one astronomer first to the whereabouts, and then to the vision of the disturbing planet.

Notwithstanding what we said about the universality of this force, and how it affects all forms of matter, it may still appear as if the air were an exception. But it is not so; the air also gravitates. The fact that it gravitates is proved in various ways. First, if it did not, it would not accompany the earth in its movements round the sun; the earth would sweep along into space, and leave it behind it. Secondly, if we place a bottle from which the air is exhausted in a balance and exactly poise it with a counter-weight, and then open it and let in the air, it will show at once that the air has weight or gravitates by immediately descending. Thirdly, if we extend a piece of india-rubber over the end of a vessel and begin to withdraw the air from it, we shall see the india-rubber sink in, under the pressure of the air outside, to fill up the space left vacant by the removal of the included air. The fact that air gravitates we have already taken for granted in explaining the ascent of a balloon; and the proofs now given are enough to show that the cause assumed is a real one. The lighter gas rises and the heavier sinks by law of gravitation.

_Gravitation and Cohesion._--Unlike the attraction of aggregation, or cohesion, which acts only between particles separated from each other by spaces that are imperceptible, gravitation takes effect at distances which transcend conception, but it diminishes in force as the distance increases. The law according to which it does so is expressed thus; its intensity decreases with the square of the distance; that is to say, at twice the original distance it is 1-4th; at thrice, 1-9th; at four times, 1-16th, for 4, 9, 16 are the squares respectively of 2, 3, and 4. To take an instance, a ball which weighs 144 lb. at the surface of the earth will weigh 1-4th of that, or 36 lb., when it is twice as far from the centre as it is at the surface; and 1-9th, or 16 lb. when it is thrice as far; and 1-16th, or 9 lb. when it is four times as far. The attraction of cohesion, on the other hand, as we say, acts only when the particles seem almost in contact, and it ceases altogether when once, by mechanical or other means, the bond is broken, in consequence of the particles being forced too near, or sundered too far from, one another.

One distinguishing difference between the attraction of gravitation and that of cohesion is, that whereas the former is uniform, the latter is variable; that is, under gravitation the attraction of any one particle to any other is the same, but under cohesion, some sets of particles are more forcibly drawn together than others. For instance, a particle of iron and a particle of cork gravitate equally, but particles of iron and particles of cork among themselves do not cohere equally. And it is just because those of the former cohere more than those of the latter, that a piece of iron feels harder and weighs heavier than a piece of cork.

Further, the attraction of gravitation is unaffected by change in the condition of bodies, while that of cohesion is. It makes nothing to gravitation whether a piece of metal is as cold as ice, or heated with a sevenfold heat. Not so to the power of cohesion; withdraw heat, and the particles under cohesion cling closer; add it, and both the spaces grow wider and the attraction feebler. Thus, for example, you may suspend a weight by a piece of copper-wire, and the wire not break. But apply heat to the wire, and its cohesion will be lessened; the force of gravitation will overpower it, rupture the wire, and cause the weight to fall.

_Cohesion_.--That the action of the attraction of cohesion depends on the contiguity of the particles in the cohering body, may be shown by an illustration. Take a ball of lead, divide it into two hemispheres, smooth the surfaces of section, then press them together, and you will find it requires some force to separate them; thus proving the dependence of cohesion on contiguity, although the effect in this case may be due in some degree to the pressure of the atmosphere as well as the power of cohesion.

Heat is the principal agent in inducing cohesion, as well as in relaxing its energy; for by means of it you can weld the hardest as well as the softest substances into one, and two pieces of iron together, no less than two pieces of wax. It is possible, indeed, by heat to unite two sufficient waxed corks to one another, so as to be able by means of the one to draw the other out of a bottle: such, in this case, is the force of cohesion induced by heat.

The power of cohesion exists between the particles of liquids as well as those of solids, the only difference being that in solids the particles are relatively fixed, while in liquids they move freely about one another, unless indeed when they are attracted to the surface of a solid--a fact we are familiar with when we dip our finger into a vessel of water. The cohesive power of liquids is overcome by heat as well as that of solids, only to a much greater degree, for under it they assume a new form, acquire new properties, and expand immensely in volume. They pass into the form of vapour, occupy a thousand times larger area, and possess an elasticity of compressibility and expansibility they were destitute of before.

There is a beautiful phenomenon which accompanies the expansion of ether under the influence of heat. Placed in a flask to which heat is applied, the ether will go off in vapour; and as the heat increases, the vapour will gradually light up into a lovely flame. The expansibility of air, which is vapour in a permanent form, can be shown by experiment. If we tie up an empty or collapsed bladder, and place it in a vessel over an air-pump, we may see, as we withdraw the air from the vessel, and so diminish its pressure, the bladder gradually expand and swell as it does under inflation.

The cohesive power of water is beautifully illustrated. Have a small barrel or bucket so constructed as to be fitted with gauze at the top; immerse it exactly, so that the water may form a film between the meshes, and then open the tap at the bottom: the water will not flow till the meshes at the top are broken by blowing on their surface. The adhesion of the particles in a soap-bubble is another illustration, no less beautiful, as well as more familiar; for the soap, which might be supposed to be the cause of the phenomenon, serves only to prevent the intrusion of dust between the particles, but by no means to intensify their attractive power.

There are some liquids the adhesiveness of whose particles is so perfect as to bar out the access of air when we strew them on the surface of other liquids; and on the Continent it is not uncommon to protect wines against the action of the atmosphere by, instead of corking the bottle, simply pouring in a few drops of oil, which, being lighter than the wine, floats on the surface. It is parallel to the instance of the barrel with the gauze-wire top mentioned above, that if we loosely plug a bottle full of liquid with a piece of cotton-wool, and invert it, the particles in contact with the wool will cohere so closely that the fluid will not be able to escape. The adhesiveness of the particles of water to a solid surface can be exemplified by allowing one of the scales of a balance to float in water and leaving the other free; the one in contact with the water will refuse to yield after we have placed even a tolerable weight in the other which is suspended in the air.

The power of cohesion is more rigorous in some bodies than others. In some cases the body will rupture if it is interfered with ever so little; in others, the particles admit of a certain displacement, and if the limits are not transgressed, they return to their original position when the compressing or distending cause is removed. This rallying power in the cohesive force is called Elasticity, and it exists in no small degree in glass. The spaces between the particles can, within limits, be either lessened by compression or increased by distension, and the particles retain their power of recovering and maintaining the relation they stood in before they were disturbed. It is the power of cohesion or aggregation which resists any disturbance among the particles, and which restores order among them when once disturbance has taken place. And not only does nature resist directly any undue interference with the cohering force, but tampering with it even slightly has often a certain deteriorating effect upon the physical properties of bodies. A bell, for instance, loses its tone when heated, because by that means its particles are disturbed; though it recovers its tone-power as it cools, and as the particles return to their places.

In organic bodies, both during growth and decay, the particles are more or less in flux; but in feathers, after their formation, the attraction of aggregation remains constant, and by means of it their particles continue fixed in their places, not only with the life of the bird, but long after. Nay, you may even crumple them up, and toss them away as worthless, and yet if you expose them to the vapour of steam, they will not only recover their form, but they can be made to look as beautiful as ever.