an autobiography-第82节
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CHRONOLOGICAL LIST OF MECHANICAL INVENTIONS AND TECHNICAL CONTRIVANCES。
by James Nasmyth。
1825。 A mode of applying Steam Power for the Traction of Canal Barges； without injury to the Canal Banks。
A CANAL having been formed to connect Edinburgh with the Forth and Clyde Canal； and so to give a direct waterway communication between Edinburgh and Glasgow； I heard much talk about the desirableness of substituting Steam for Horse power as the means of moving the boats and barges along the canal。 But； as the action of paddle wheels had been found destructive to the canal banks； no scheme of that nature could be entertained。 Although a tyro in such matters； I made an attempt to solve the problem； and accordingly prepared drawings； with a description of my design； for employing Steam power as the tractive agency for trains of canal barges； in such a manner as to obviate all risk of injury to the banks。
＇Image＇
The scheme consisted in laying a chain along the bottom of the canal； and of passing any part of its length between three grooved and notched pulleys or rollers； made to revolve with suitable velocity by means of a small steam…engine placed in a tug…boat； to the stern of which a train of barges was attached。* ＇footnote。。。 Had this simple means of 〃tugging〃 vessels through water…ways been employed in our late attempts to ascend the rapids of the Nile； some very important results might have issued from its adoption。 。。。＇ The steam…engine could thus warp its way along the chain； taking it up between the rollers of the bow of the tug…boat； and dropping it into the water at the stern； so as to leave the chain at the service of the next following tug…boat with its attached train of barges。 By this simple mode of employing the power of a steam…engine for canal boat traction； all risk of injury to the banks would be avoided； as the chain and not the water of the canal was the fulcrum or resistance which the steam…engine on the tug…boat operated upon in thus warping its way along the chain； and thus effectually； without slip or other waste of power； dragging along the train of barges attached to the stern of the steam…tug。 I had arranged for two separate chains； so as to allow trains of barges to be conveyed along the canal in opposite directions； without interfering with each other。
I submitted a complete set of drawings； and a full description of my design in all its details； to the directors of the Canal Company； and I received a complimentary acknowledgment of them in writing。 But such was the prejudice that existed； in consequence of the injury to the canal banks resulting from the use of paddle Wheels； that it extended to the use of steam power in any form； as a substitute for ordinary horse traction； and although I had taken every care to point out the essential difference of my system （as above indicated） by which all such objections were obviated； my design was at length courteously declined； and the old system of horse traction continued。
In 1845 I had the pleasure to see this simple mode of moving vessels along a definite course in most successful action at the ferry across the Hamoaze at Devonport； in which my system of employing the power of a steam…engine on board the ferry boat； to warp its way along a submerged chain lying along the bottom of the channel from side to side of the ferry； was most ably carried out by my late excellent friend； James Rendell； Esq。； C。E。； and is still； I believe； in daily action； giving every satisfaction。
1826。 An Instrument for Measuring the Total and Comparative Expansion of all Solid Bodies。
My kind friend and patron； Professor Leslie； being engaged in some investigations in which it was essential to know the exact comparative total expansion in bulk of metals and other solid bodies； under the same number of degrees of heat； mentioned the subject in the course of conversation。 The instrument at that time in use was defective in principle as well as in construction； and the results of its application were untrustworthy。 As the Professor had done me the honour to request me to assist him in his experiments； I had the happiness to suggest an arrangement of apparatus which I thought might obviate the sources of error； and； with his approval； I proceeded to put it in operation。
My contrivance consisted of an arrangement by means of which the metal bar or other solid substance； whose total expansion under a given number of degrees of heat had to be measured； was in a manner itself converted into a thermometer。 Absolutely equal bulks of each solid were placed inside a metal tube or vessel； and surrounded with an exact equal quantity of water at one and the same normal temperature。 A cap or cover； having a suitable length of thermometer tube attached to it； was then screwed down； and the water of the index tube was adjusted to the zero point of the scale attached to it； the whole being at say 50deg of heat； as the normal temperature in each case。 The apparatus was then heated up to say 200deg by immersion in water at that temperature。 The expansion of the enclosed bar of metal or other solid substance under experiment caused the water to rise above the zero； and it was accordingly so indicated on the scale attached to the cap tube。 In this way we had a thermometer whose bulb was for the time being filled with the solid under investigation；the water surrounding it imply acting as the means by which the expansion of each solid under trial was rendered visible； and its amount capable of being ascertained and recorded with the utmost exactness； as the expansion of the water was in every case the same； and also that of the instrument itself which was 〃a constant quantity。〃
In this way we obtained the correct relative amount of expansion in bulk of all the solid substances experimented upon。 That each bar of metal or other solid substance was of absolutely equal bulk； was readily ascertained by finding that each； when weighed in water； lost the exact same weight。
＇Image＇ James Nasmyth's Expansometer； 1826。
My friend； Sir David Brewster； was so much pleased with the instrument that he published a drawing and description of it in the Edinburgh Philosophical Journal； of which he was then editor。
1827。 A Method of increasing the Effectiveness of Steam by super…heating it on its Passage from the Boiler to the Engine。
One or the earliest mechanical contrivances which I made was for preventing water； in a liquid form； from passing along with the steam from the boiler to the cylinder of the steam…engine。 The first steam…engine I made was employed in grinding oil colours for my father's use in his paintings。 When I set this engine to work for the first time I was annoyed by slight jerks which now and then disturbed the otherwise smooth and regular action of the machine。 After careful examination I found that these jerks were caused by the small quantities of water that were occasionally carried along with the current of the steam； and deposited in the cylinder； where it accumulated above and below the piston； and thus produced the jerks。
In order to remove the cause of these irregularities； I placed a considerable portion of the length of the pipe which conveyed the steam from the boiler to the engine within the highly heated side flue of the boiler； so that any portion of water in the liquid form which might chance to pass along with the steam； might； ere it reached the cylinder； traverse this highly…heated steam pipe； and； in doing so； be converted into perfectly dry steam； and in that condition enter the cylinder。 On carrying this simple arrangement into practice； I found the result to be in every way satisfactory。 The active little steam…engine thence…forward performed its work in the most smooth and regular manner。
So far as I am aware； this early effort of mine at mechanical contrivance was the first introduction of what has since been termed 〃super…heated steam〃a system now extensively employed； and yielding important results； especially in the case of marine steam…engines。 Without such means of supplying dry steam to the engines； the latter are specially liable to 〃break…downs；〃 resulting from water； in the liquid form； passing into the cylinders along with the steam。
1828。 A Method of 〃chucking〃 delicate Metal…work； in order that it may be turned with perfect truth
In fixing portions of work in the turning…lathe； one of the most important points to attend to is； that while they are held with sufficient firmness in order to be turned to the required form； they should be free from any strain which might in any way distort them。 In strong and ponderous objects this can be easily accomplished by due care on the part of an intelligent workman。 It is in operating by the lathe on delicate and flexible objects that the utmost care is requisite in the process of chucking； as they are easily strained out of shape by fastening them by screws and bolts； or suchlike ordinary means。 This is especially the case with disc…like objects。 As I had on several occasions to operate in the lathe with this class of work I contrived a method of chucking or holding them firm while receiving the required turning process； which has in all
