170 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[May, 



all further trouble of invention and criticism, should we not contemn their 

 poverty of spirit and negation of mind ? Would not the historian, the ar- 

 tist, and the tasteful observer, have to deplore the absence of that internal 

 evidence and hieroglyphic character of the times, which adds such a relish to 

 the architectural remains of our fair and beloved country ? 



But let us suppose that either of these monarchs had been enlightened by 

 the art of a Raphael or a Michael Angelo, or by the sculptures of a Phidias, 

 which he might even affect to appreciate and to be proud of; and that we 

 should learn by historical record that he had said — " We are so anxious to 

 carry out the style of former days that we shall shut our eyes to those ex- 

 cellencies of sculpture and of fine art, and force our artists to copy the ob- 

 scenities and senseless carvings of those barbarous times ; simply that we 

 may carry out the imitation of the style in all respects." 



Restoration, indeed, is a different consideration, and the happiest result of 

 this taste is, that we reinstate, for centuries to come, those venerable anti- 

 quities to which we have so many reasons of attachment. The restoration 

 of the Palace at Westminster may find under this consideration a sufficient 

 apology. But for works altogether new such a system of imitation is not 

 reconcileable with our pretensions to genius and enlightenment ; and it does 

 appear that there is in it a vice of mind or of industry for which posterity 

 will visit us. Such an indifference as to choice of styles indicates, in fact, 

 an absence of culture and perception of the really fit, and beautiful, and 

 great — a state of mind which, in religion, politics, or morals, would be ac- 

 counted fatal to improvement, and the sure forerunner of every heresy. 

 D'Ageneourt attributes to this spirit of imitation tinder the Emperor Had- 

 rian the decline of taste in Rome. 



The learned in Paris deplore it not only under this apprehension, but as 

 the imposition of anachronisms on posterity, and as the falsification of the 

 pages of history, in its most interesting and characteristic traits. " Have 

 we not," as says Isaiah, " a lie in our right hand ?" 



It is very important that the merits of that question should be debated in 

 a candid spirit, and that the true grounds of a style should be investigated 

 by the rules of sound criticism ; as how far architecture has ever been and 

 should be the picture in which all the discoveries of mechanics, of materials 

 and of industry, are to he exhibited and recorded; and whether the suc- 

 cessive changes of style have not been chiefly owing to the progressive dis- 

 coveries and improvements on workmanship, materials, and convenience. 

 How far the combinations of this art are capable of displaying the intellec- 

 tual character of an age and people, and what should be the just bounds and 

 limits of association, authority, and imitation. 



Finally, let us never forget the pregnant saying of the great Schiller: — 



The artist is the son of his time ; 

 Happy for him if he is not its pupil ; 

 And happier still if not its favourite. 



In conclusion, the Professor expressed the gratification he had felt in 

 the attention paid by the students to this course of lectures; not as it re- 

 flected upon himself personally, but as it gave the strongest possible evi- 

 dence of the ardour and assiduity with which they pursued their studies: 

 for he could with great sincerity assure them that, amongst the achievi 

 of a very long period of singleness and devotion to his profession, he should 

 consider that the most glorious, which bad contributed to the instruction, 

 and warmed the enthusiasm of those rising talents destined perhaps in future 

 ti:i s to adorn and illustrate our country. 



INSTITUTION OF CIVIL ENGINEERS. 



Feb. 7. — The President in the Chair. 



"Description of a Drawbridge at Bowcomle irrvk, near Kingsbridge, 

 Devon." By George Clarisse Dobson, Assoc. Inst. C.E. 



This drawbridge spans one of five openings in a stone bridge, built across 

 a navigable branch of Salcombe Harbour; it is in one leaf, 15ft. 9in. wide, 

 and 32 ft. long, from out to out, supported upon a cast iron shaft or axle, 

 placed 7ft. Gin. from the inner end, working in the abutment pier, which is 

 built hollow to receive it, and thus the part within the axle end acts as a 

 counter weight. To the centre of the end cross-beam of the counter part, a 

 chain is attached, and after passing over cast iron sheaves in the masonry of 

 the face of the abutment, is coiled on a drum fixed on a horizontal shaft, 

 carrying on one end a pinion, worked by a rack, attached to the piston of 

 the hydraulic press ; by this means, motion is given to the shaft and drum, 

 and consequently to the leaf of the bridge. Balance boxes are hung to the 

 counter end, by which the shutting is regulated. The struts for supporting 

 the leaf, when raised, are also thrown in and out of their places by a rack 

 and pinion. The hydraulic press used for opening and closing the bridge, is 

 simple in its construction, and the whole works so easily, that a female can 

 open and close the bridge in about 15 minutes without difficulty. The fresh 

 water used for the pump is contained in a cistern beneath, and seldom wants 

 replenishing, as it is returned into the reservoir every time after being used. 

 The bridge was designed and erected by Mr. J. M. Rendel, about 12 years 

 since, when he was engaged in improving the turnpike road in the south of 

 Devon. The expense of repairing, oiling, packing, &c, since its erection, has 



averaged under "/. per annum, including a small salary to a neighbouring 

 millwright for occasional inspection. The communication is accompanied bv 

 a drawing, showing a plan and sectional elevation of the bridge and the 

 machinery. 



On Frictiox. 



" An Investigation of the comparative loss by Friction, in beam and direct 

 action Steam Engines." By William Pole, Assoc. Inst. C. E. 



In consequence of the comparatively recent introduction of direct action 

 steam engines on board the steam vessels of the Royal Navy, the attention 

 of engineers has been drawn to the advantages or disadvantages they possess, 

 when viewed in comparison witli those constructed with side levers. The 

 object of this paper is to investigate the value of an apparently formidable 

 objection which has been frequently urged against the direct action engine, 

 namely, " that from the more oblique action, consequent upon the shortness 

 of the connecting rod, the loss by the increase of friction is so considerable 

 as to constitute a serious objection to this form of engine." After explain- 

 ing to what extent mathematical analysis is applicable for determining the 

 amount of friction, the paper proceeds to show that it may be satisfactorily 

 used in the present case, as it is only the friction caused by the strain, or 

 load, which is involved in the objection, and this is more adapted for theo- 

 retical than experimental determination. 



The three general laws of friction, as established by the best experiments, 

 are, 



1st. That the friction caused by one solid body rubbing upon another, is 

 independent of the velocity with which the rubbing surface moves. 



2nd. It is also independent of the area of the rubbing surface. 



3rd. It is proportional to the pressure upon this surface.' 



From these it will follow, that if the pressure upon a moving body be 

 nndtiplied by a certain co-efficient of friction (whose value is dependent upon 

 the nature of the rubbing surface), the product will be the resistance from 

 friction; and this multiplied again into any space the rubbing surface moves 

 through, will give the amount of " power, work, or labouring force," ex- 

 pended in overcoming the friction through that space.- If the pressure upon 

 the moving body be variable throughout its motion, the differential calculus 

 must be employed, but the principle of calculation is still the same. 3 



The paper proceeds to deduce general mathematical expressions for the 

 amount of friction on each bearing of an engine, by finding, first, by ordinary 

 statical rules, the pressure thrown on each particular hearing by a given force 

 applied to the piston, and then combining this with the space through which 

 the rubbing surface moves. This is done for the beam engine, and for three 

 modifications of the direct action engine. Equations are also added for the 

 oscillating or vibrating engine, and for an arrangement in which the con- 

 necting rod is supposed to be indefinitely lengthened. The numerical values 

 of the expressions for friction thus found, are then calculated for an engine 

 upon each of these different constructions, supposing them to be similar in 

 all other respects, having the cylinders tiG inches in diameter, with a length 

 of stroke of 6 feet j and the results are shown in a table, distinguishing the 

 friction of every bearing. From this it appears that as respects the friction 

 caused by the strain, if the beam engine be taken as the standard of com- 

 parison — 



The vibrating engine has a gain of .. l'l percent. 



The direct action engine with slides loss .. 1*8 „ 



Ditto with rollers gain . . 0-8 „ 



Ditto with a parallel motion gain . . 1-3 „ 



This difference being so trifling, it is contended that the objection to the 

 direct action engine, on the ground of its alleged increased friction, has, 

 when investigated, no adequate foundation. 



Mr. Field believed that the paper was correct in its view of the comparative 

 amount of friction of the two kinds of engines. He was of opinion that an 

 excessive allowance for friction had hitherto been generally made in calcu- 

 lating their effective power. It was found practically, that when the pressure 

 upon the piston was about 121b. per square inch, the friction did not amount 

 to more than 1 lb. or 1 Jib. per square inch. This was easily ascertained by 

 the indicator, when the engine was working without a load, but when loaded, 

 he knew of no accurate experimental mode of showing it. At the engines of 

 the Blackwall railway, the experiment had frequently been tried, by casting 

 oft" all the load, and so regulating the steam, that the engines should make 

 only the regular number of strokes per minute ; the result had invariably 

 shown about 1 lb. per square inch for friction. 



Mr. Taylor confirmed the preceding remarks ; it had been the custom for- 

 merly in large pumping engines to allow one-fifth for friction, but modern 

 practice had shown that this was not necessary, particularly since greater 

 precision had been introduced into the construction of all kinds of ma- 

 chinery. 



Mr. Miller agreed that the friction of engines generally had been over- 



1 Poisson, Traite de Mecanique, 2nd edition, art. 456. 



2 If »i =the co-efficient of friction, P= the pressure, and S = the space 

 moved through, then the power expended = tn PS. 



' Let x be any space moved through : let X represent the variable pres- 

 sure, expressed in terms of x, then the power expended -m/X </.<-. 



