1841.] 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



397 



what he termed the " percussive action of steam ; " he beheved that the 

 superior economy of the Cornish engines, as far as related to the action of 

 steam in the cylinders, would be found to be due to the amount of the ex- 

 pansion of the steam ; which depended, not only upon the opening and 

 closing of the steam valve, but also upon the greater or less area of the 

 aperture of the throttle valve. It was evident, that on closiTig the steam 

 valve, the space between it and the throttle valve would be filled with steam 

 of a density nearly, or quite, equal to that in the boiler; therefore, on the 

 first admission of the steam into the cylinder, it might be presumed to act 

 upon the piston with that pressure ; considering, likewise, that a short inter- 

 val of time necessarily occurs for setting in motion the beam, with the heavy 

 pump rods appended to it ; but immediately the piston starts, expansion 

 takes place, as the throttle valve prevents the steam from following the pis- 

 ton freely, so that a greater degree of expansion must take place when the 

 steam is at a higher density; for the throttle valve being then more closed, 

 offers a greater resistance to the steam following the piston. The indicator 

 diagram of the East Crinnis Engine showed this efl^ect to a certain extent, 

 although neither in that nor in the diagram of the Huel Towan Engine was 

 there nearly the same degree of pressure exhibited in the cylinder at the 

 commencement of the stroke, as in the boiler ; but it was evident that those 

 diagrams coidd not be relied upon, as they did not account for the whole 

 duty done by the engines, either on the percussive or the expansive principle. 

 -Assuming a bushel of coal to weigh 941b. as generally reckoned in Cornwall, 

 and that 1ft. of coal would evaporate lOUb. of water, it could readily be 

 shown, that the quantity of water converted into steam by one bushel of 

 coal, would, when expanded in a cylinder, during ^ of the stroke, lift up- 

 wards of 257 million tb. one foot high in one minute; which was a much 

 greater duty than was realized by atiy Cornish engine. 



Mr. Seaward allowed that Mr. Parkes had clearly shown, that a certain 

 amount of effect was due to the sudden impact of the steam upon the piston 

 of a pumping engine. Whether the term " percussion," as applied to this 

 action, was the proper one, he would not then examine ; but the effects 

 shown to have been produced, and the phenomena attendant upon the ex- 

 hibition, were so remarkable, that he conceived the subject to merit the most 

 deliberate investigation of engineers as well as philosophers. He had pre- 

 viously objected to the theory, on the ground that the effect could only be 

 in the ratio of the weight of the steam multiplied into its velocity ; but he 

 believed the subject must be examined in a different manner ; and although 

 the principle must always have existed, it was only in consequence of modi- 

 fications in the application of steam, that the effects had been so fully de- 

 veloped. 



Mr. Parkes mentioned, that since his paper had been written, he had found 

 an experiment which was strictly analogous to his proposition. It was re- 

 lated by Mr. Robins, who was so justly celebrated as a mathematician and 

 philosopher, and first discovered that the gas evolved from gunpowder was 

 a permanently elastic fluid : " when gunpowder is fired in an exhausted re- 

 ceiver, the mercurial gauge instantly descends upon the explosion, and as 

 suddenly ascends again, .\fter a few vibrations, none of which, except the 

 first, are of any great extent, it fixes at a point which indicates the density 

 of the inclosed gas." He considered this result as corroborating those ob- 

 tained by himself, as well as justifying the comparison he had drawn between 

 the instantaneous action of gunpowder gas and steam. .Mr. Robins's words 

 precisely described the steam's action, as traced on the indicator diagram 

 exhibited. The springing of the cylinder cover referred to, and in the man- 

 ner stated, must, he thought, satisfy every one, that the steam's instantaneous 

 action far exceeded in effect that of its simple elastic force, which was proved 

 to have been unequal to produce any change in the parallelism of the cover. 

 As regarded Mr. Homersham's investigation of the power of the steam in 

 the Huel Towan engine, it was correct that the initial steam was in a state 

 of expansion during ^§ of the stroke, but not all the steam, for it had not all 

 entered the cylinder until the piston had travelled through nearly ^ of the 

 stroke. His calculations were, therefore, hypothetical, and not in accordance 

 with the facts of Mr. Henwood's experiment. 



THE CALEDONIAN CANAL.— THIRTY-SIXTH REPORT OF THE 

 COMMISSIONERS. 



Few undertakings have been more singularly and uniformly unfortunate 

 than the one which forms the subject of the present report. 



Though originating in the purest and most praiseworthy motives, though 

 directed by the talents of a Telford, and supported and carried out by an 

 almost unlimited supply of public money, this canal appears to have arrived 

 at such a point of dilapidation and decay, and to be attended with such pe- 

 culiar difficulties, that it has at length become equally impossible either to 

 advance or recede, without incurring a further enormous outlay and expense. 



In this situation, and as the lesser evil, it would appear that a select com. 

 mittee of the House of Commons, appointed in 1839, for the purpose of ex. 

 amining into the affairs of the canal, made a report, wherein they recom. 

 mended that a further advance of public money to the amount of ,€200,000 

 should be made, for the purpose of completing and finishing it properly anj 

 effectually, so as to render it available for the purposes for which it was or;, 

 ginally intended, giving it as their opinion, that inasmuch as a vast sum q^ 



money had already been expended on the concern, which, though at present 

 unproductive in a pecuniary point of view, had still, to a certain extent, been 

 beneficial to the country through which it passed ; and as destroying the 

 works, filling up the canal, or abandoning the undertaking altogether, must 

 be attended wilb a further expense for the purpose of making the country 

 secure from inundation, which expense would amount to as much a« would 

 put the canal in good working condition and repair, they felt that tlie choice 

 left them was only one of two positive evils, either of which must be attended 

 with an equal outlay, and that, therefore, it was not advisable to sink the 

 money already expended and put up with the dead loss; but rather, by ex- 

 pending the same money in rendering the canal more easily navigable, and 

 more adapted to the purposes of commerce, to take the chance which, though 

 remote, might yet by possibility render the undertaking sufficiently productive 

 to pay its own expenses, and thus leave it, if not a positive benefit to the 

 present generation, in a commercial point of view, at least a gigantic monu- 

 ment to posterity of British industry, ingenuity, and talent. 



In order to account for the enormous but fruitless outlay of the public 

 money, which, in the present instance, has already exceeded £1,000,000 

 sterling, without including the £200,000 above-mentioned, it will be neces- 

 sary to go back into the origin of this undertaking, and to trace the causes 

 which have led to tliis unsuccessful result. 



It would appear that, in the year 1803, France having, by successive ag- 

 gressions, arrayed the whole of Europe, and more especially the great 

 northern Powers, against her great maritime rival, and there being no naval 

 station of any consequence in the north of England, the whole coast of Scot- 

 land or the north-west of Ireland, the enemy had it in his power to annoy 

 this part of the country from the North Sea, I)y passing round the Orkney 

 Islands, whereby the commerce of a considerable portion of the United 

 Kingdom frequently suffered great and serious losses. This circumstance, 

 and the idea of affording employment to the inhabitants of the highlands of 

 Scotland, who at that time were in great distress, and were rapidly emigrat- 

 ing from home, were much pressed on the attention of the Government of 

 that day. and caused the subject to be taken into serious consideration, and 

 enlarged views were developed by describing the singular valley called the 

 Great Glen of Scotland, which, commencing between the promontory of 

 Burg Head in Elgin and Cromarty, passes through a succession of sea inlets 

 and fresh water lakes to the soutern extremity of Cantyre, for a distance of 

 200 miles, and in nearly a straight direction between the Naze of Norway 

 and the north of Ireland, and which, it was alleged, afforded great facilities 

 for internal navigation. It was said that the whole of this extensive valley, 

 with the exception of 22 miles, being occupied by navigable waters, and the 

 excepted space by a navigable canal, would save upwards of 500 miles of 

 dangerous navigation. 



\Vith these views the Caledonian Canal was originally undertaken; but 

 though there can be no doubt that the natural features of the country sug- 

 gested the plan, yet it is doubtful whetlier it would ever have been enter- 

 tained but for the distressed state of the Highland population, which it was 

 an object to relieve, by affording them employment, and this being best at- 

 tained by extensive public works, was the immediate cause which led to the 

 adoption of the scheme. 



Accordingly Telford was employed to examine the line of country indicated, 

 and liaving testified to its practicability he was alone employed to carry the 

 design into execution, agreeably to a plan he had furnished. 



By this plan it was proposed to form a canal large enough to admit of the 

 navigation of a 32-gun frigate throughout its whole length, and the estimated 

 cost of the work in question was fixed by him at an amount of £350,000. 

 This estimate was subsequently increased to £474,500, but which latter sum 

 fell very far short of the real expense incurred in the undertaking. This sin- 

 gular difference between the estimate and the real cost was said to arise from 

 the fact, that subsequently to the estimate being given in, a serious rise had 

 taken place, as well in the value of timber as in the cost of labour (conse- 

 quent on the rise in tlie price of provisions), and something must also be 

 attributed to the want of experience in estimating the cost of works of such 

 a gigantic nature ; from these causes, ami from other unforeseen difficulties, 

 the canal was not opened to the public until many years had elapsed from 

 the time of its commencement. 



In the meanwhile, and during the period wherein these works were going 

 forward, the enormous inaccuracy of the estimates became every day more 

 apparent, and much opposition was manifested in various quarters to any 

 further advance of the public money towards carrying out the objects of the 

 scheme ; under these circumstances, and finding increased difficulty in raising 

 the supplies necessary to complete the work, the commissioners determined 

 to open the canal to the public in its unfinished state, and accordingly, in 

 1822, the canal, though only partly completed, was opened to the public, 

 and in which state it has remained up to this time. 



The consequence of this premature opening led to numerous accidents and 

 misfortunes, and to frequent interruptions of the navigation. 



Up to the time of opening the canal, the expences of its construction had 

 amounted to the enormous sum of £905,258, which amount h,id in May, 

 1839, been increased to £1,023,628, exclusive of a debt to the Bank of Scot- 

 land of £39,146. 



From the very first hour of its being opened to the public, the canal, in a 

 pecuniary sense, has been a losing concern, never having paid even the ex- 

 penses of keeping it in repair, much less leaving any surplus available to the 

 liqiudatiou of its debts. On the contrary, the commissioners have been com- 



3 G 



