392 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



[Dec. 



or motion required — the engine will work with sufficient regularity for all 

 orrjioary purposes." 



. The last paragraph is rendered ambiguous liy the vague use of the 

 word " power." The " power resident in the fly-wheel," we presume 

 to mean its r(8 tira, or miss multiplied by the square of its velocity 

 — in fact, tliere can be no otlier measure of the porter of a fly-wheel. 

 The " power generated by the engine in one half-stroke," probably 

 signifies " vvork done," or the pressure on the piston multiplied by 

 the distance through whicii it acts. This " work done " is always 

 equivalent to a determinate amount of r/s viva; that is, if it acted on 

 a body or bodies subject to no prejudicial resistances, would produce 

 n certain calculable velocity, such that the ri's viva would be the 

 same, whelhi'r the mass acted on were small or great. Consequently, 

 Mr. Bourne's rule may be stated thus: — when the engine is in its 

 normal state of working, the vis viva of the flv-wheel must be twu- 

 nnd-a-half to four times greater than the vis viva which tlie engintr 

 would produce during a half-stroke. For example, if the mass of 

 the fly-wheel (supposed to be collected at its rin.) were M, and V 

 the linear velocity with which it generally moved, M V" would be its 

 actual vts viva. Suppose that if the engine could act on the fly-wherl 

 ezclunivtli/ for a hali'stioke, the velocity generated would be ;•; the 

 corresponding bypotli' tical vis visa vvould be Mo°; and adopting the 

 higlu'st of Mr. Bourne's ratios, we should have 



4 M V^ — M c', or 2 V = », 



which would reduce tlie rule to a simpler form, as follows : — the 

 mass of the fly-wheel must be so cliosen, that the velocity which the 

 engine mould produce in it by acting on it exclusively for half a stroke 

 may be half its actual velocity when the engine is in its ordinary 

 state of working. 



We have endeavoured to develope the rule in the above manner, 

 not from its intrinsic value, but m^'rely to illustrate the extreme im- 

 portance of adhering, in all mechanical disquisitions, to measures of 

 force about which there cannot be any possible ambiguity. The use 

 of vague phrases to indicate the various effect of forces is the true 

 cause of the dithcultv of the subject. If a precise, systematic nomen- 

 clature were universally understood and adopted, there would be far 

 fewer of the idle discussions of principles with which we and our 

 contemporaries are bored, and far less money would be spent iu 

 securing by patent the exclusive right of eftecting impossibilities. 



With respect, however, to the intrinsic value of the above rule 

 respecting the fly-wheel, it is to be observed that it can only apply to 

 engines performing a particular cbiss of duties. The duties may task 

 the engine in suih an equable and uniform manner, that no fly-wheel 

 need be required. Or, again, the resistances may be capable of such 

 great fluctuations, that a fly-wheel of enormous dimensions may be 

 required. The variation of resislances is not taken into account in 

 Mr. Bourne's rule. A fly-wheel is a kind of bank in which force is 

 treasured up in times of abundance, to be redistributed in times of 

 scarcity. The greater the superabundance at one ])eriod, and de- 

 ficiency at another, the greater must be the capacity of the bank. 



Another doctrine adopted in this treatise, and which seems liable 

 to lead to erroneous conclusions, is the following: — 



" Settinp; aside loss from friction, and supposing the vacuum to be a per- 

 fect one, tliere would be no benefit arising from the use of steam of a high 

 pressure in cuudeiisiog engines, for the same weight of steam used witliout 

 expansion, or with the same measure of expansion, would produce at 

 every pressure the same amount of mechanical power. A piston, with a 

 square foot of area, and a stroke of three feet with a pressure of one at- 

 mosphere, would obviously lift the same weight through the same distance, 

 as a cylinder with half a square foot of area, a stroke of three feet, and a 

 pressure of two atmospheres. In the oue case, we Jiave three cubic feet of 

 steam of the pressure of one atmosphere, and in the other case 1.^ cubic feet 

 of the pressure of two atmospheres. But there is the same weight of 

 steam, or the same quantity of heat and water in it, in both cases, so that 

 it appears a given weight of steam would, under such circumstances, pro- 

 duce a deljnile amount of power, without reference to the pressure." 



Tills reasoning seems to overlook the gain of mechanical effect re- 

 sulting from tile employment of very high-pressure steam used with 

 a great degree of expansion. Theoretic. dly, the higher the steam- 

 pnssure, the greater will (by working expansively) be the power 

 obtained from a given quantity of fuel. It may be assumed that a 

 pound of coke or coal will evaporate the same quantity of water at 

 any pressure. The steam produced, therefore, will, while acting at 

 full pressure, or unexpansively, effect the same amount of work iu 

 both cases. But when the steam is cut off and expanded, more woik 

 will be got out of the higli-pressure steam than the low-pressure ; for 

 the former may be expanded to a greater degree than the latter, be- 

 fore it become so weakened as to be incapable of further useful effect. 

 The use of high-pressure steam is not so indifferent a matter as the 

 above quotation seems to suggest. Setting aside_ the question of 



safety, th» higher the pressure of the steam the greater will be the 

 econuiny of fuel, supposing the expansion always carried to that point 

 where the steam ceases to act beneficially. A mistake on this point 

 seems to have led Mr. Bourne to say further on, that " the superior 

 economy of the Cornish boiler is not derived from anv peculiarity of 

 form and arrangement, but from the immense extension of heating 

 surface." 



In treating of the resistance to the motion of railway trains, Mr. 

 Bourne falls into th' common error of assuming that the rapid increase 

 of resistance resulting from the increase of velocity is due to the 

 action of the air. This resist.ince is only one item in the calculation, 

 and is often (we are inclined to thinkj a very small oue. The deflec- 

 tion and vibration of the rails, concussions at their joints, strains from 

 the wlieels or axles being slightly twisted, and the thousand-and-one 

 jolts, jars, rattlings, and vibrations inseparable from rapid motion 

 absorb the greater part of the power required at high velocities. 



In alluding to one or two deficiencies in the present treatise, we 

 would by no means have it inferred that they are samples of the 

 whole book. On the contrary, the information conveyed seems gene- 

 rally very trustworthy, and it has the advantage of being communi- 

 cated in an intelligent manner. Had we space to dilate on tiie chief 

 merits of this work, we might have chosen numerous texts for the 

 purpose — among others, the excellent account of the present state of 

 knowledge respecting the performance of marine screw-propellers, 

 and the clear descriptions given of various details of the mechanism 

 of locomotive engines. 



^ History of the Architecture of the Abbey Church of St. Alban, 

 tvith esj^ectal Reference to the Xorman Structure. By J. C. BuctLER 

 and C. A. Buckler. London : Longmans, 1S47. 



We had hoped to have had more space for our notice of the valuable 

 work of Messrs. Buckler, but we find that with the close of our volume, 

 we have too many subjects claiming our attention, and yet we do not 

 like to delay what is an act of justice towards the authors. We can- 

 nut but feel that the design of the work, that of giving a complete 

 account of the Norinau architecture of the Abbey at St. Alban's, is 

 highly praiseworthy, and is carried out in a conscientious spirit of 

 labour. The history of Matthew Paris has been particularly valuable 

 to the authors, and they iiave made very good use of it, the old 

 monkish annalist having shown an earnest desire to commemorate 

 everything of interest in connexion with the building and its abbots. 

 He lived, too, at a time when the most important works were carried 

 on for its adornment, and we can hardly help wishing he had given 

 us still more informaiion as to details, though really we owe him, as 

 it is, a large debt for what he has so copiously recorded. 



By a careful collation of such records with the present building, 

 Messrs. Buckler have been able to reproduce the old Norman struc- 

 ture, and to give us a lively picture of such a building in its pristine 

 and palmy state. This makes the work, what naturalists would call 

 a monograph — a well described account of a fine specimen, and is 

 therefore very useful to practical men, who have occasion to study or 

 apply the Norman style. 



The Norman abbey church is one of the first class as to size, for its 

 length from east to west was 44U feet, forming a long Latin cross, and 

 having a transept of 17G feet in length, and a lofty lantern lower in 

 the choir. The long nave of thirteen bays may be considered one of 

 the grandest parts of the structure, though perhaps the breadth was too 

 small for the vast length. The authors remark that particular regard 

 seems to have been paid to laying out the plan of the church, and 

 fixing the positions of the piers. Measurement has proved the ex- 

 treme accuracy of this part of the work. There is not, however, such 

 coralorniity in the superficies of the walls and pilasters, and their re- 

 treating members, though the appearance of the building generally is 

 correct. When we consider the imperfect organisation ol labour and 

 machinery in those days, the merit is very great. 



The materials employed being chiefly from the remains of the Ro- 

 man city of Verulamiuin, give a peculiar character to the building, 

 and the more particularly a^- ihe want of stone in the neighbourhood 

 led to the use of cement as a covering in some places. Where this 

 has been stripped oft', the appearance of the building is much injured ; 

 but it has enabled Messrs. Buckler to give many iuteresting drawings 

 illustrative of the details of construction. 



It is noticed that the upright line of the w dis is preserved through- 

 out their height, which measures GS feet 3 inches from the original 

 pavement in the nave, 'i'here is, however, a deviation in the exterior 

 of the lantern tower, which has pyramidal sides up to the belfry stage, 

 above which they are perpendicular, while the contignatiou is ar- 

 raigned as being abrupt, and not altogether pleasing. 



