936 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



fAuOVST, 



sculptor. And lot me remark, that there are some thing--; which 

 110 patriotism or spirit of nationality will accimiplish. It will never 

 make a man of taste admire an ordinary paintinj; or an nnirraceful 

 statue ; it will never reconcile him to a meagre elevation of an ill- 

 desiffned puhlic liuildinff. 



1 have generally attem|)teil, in my papers which I have had the 

 honour to read at tlie Institute, to show the influence which the 

 public institutions under consideration might have np(m the charac- 

 ter and destiny of the Rcjmans ; and perliajis there is much more 

 connection than at first sight a])pears between the works of the 

 architect and the national character of the jjcople. The architect 

 is called upon to create only those works which are suitable to the 

 liabits (d' the people, and his object should be to study to do these 

 well; and I, for one, do not regret that he is now compelled to 

 study the construction of churches and schools, rather tlian that of 

 theatres and porticoes. I am more tlian satisfied with the unarchi- 

 tectural erections of Covent-Garden and Drury-Lane for theatres; 

 and for porticoes and groves V'auxhal and the Surrey Zoological 

 Gardens. 



I am still compelled to speak only of the comjiarative innocence 

 of our places of public resort; they are immeasurably inferior in 

 architectural beauty, but they are a great improvement upon the 

 moral aspect, and the restraints and the reflective influence of 

 Christianity have even reached our public amusements. We can- 

 not wonder at the indignation with which the early Christian 

 writers viewed the theatres and places of public entertainment 

 among the Romans, where every brutal passion or lascivious desire 

 was gratified, and where vice in every form was enthroned by uni- 

 versal sufl^rage. We can excuse these holy men applying to these 

 rendezvous of iniquity the title of " Devil's houses," for which I 

 would hope no member of this Institute will ever have to give a 

 plan. It is to my mind a ha])py circumstance that the cnvea is 

 now transferred to the lecture-room, the orcliextni transformed 

 into an Exeter-hall platform, the ntnije to the floor of the House 

 of Commons, where sometimes members ofl'er to die, and the ])iil- 

 pitum to the place from which the peojde are instructed in the 

 truths and duties of Christianity. You w ill excuse me, then, if I 

 rather rejoice over the ground you have lost in modern times for 

 the exercise of your beautiful art ; and that rit// jirofession has so 

 amply supplied, by the sacred edifice, the field that is gone from 

 you in the profane. I rejoice, not because either you or I have a 

 stage more or less for our exertion, but because I think that the 

 best interests of mankind and the happiness of the human race are 

 more likely to be promoted by a church than by a theatre ; and if 

 we compare the national tastes of two neighbouring and rival 

 countries in this respect, we at least shall be satisfied with the 

 results ; — and although I am loath to end this paper with a senti- 

 ment that may sound harsh to some, I cannot but be of opinion, 

 that as the influence of Christianity prevails, and sober-minded 

 pursuits follow as a matter of course in its train, theatrical repre- 

 sentations, except for children, will give place ; meanwhile, what- 

 ever tends to purify our places of public resort, and make them 

 really places of recreation, is a benefit conferred on the morals of 

 the rising generation. 



THEORY OF STEAM-ENGINES. 



Account cff the e.tperimeuts undertaken by order of the Minister 

 of Public Works, France, upon the recommendation of the Central 

 Committee upon Steam-Engines, to determine the principal laws and 

 numerical data which enter into the calculation of Uteam-Engines. 

 By M. V. Regnault.* 



Introduction. — The theoretic calculation of the work done by 

 steam-engines is founded upon some incontestable principles of 

 general mechanics, and upon several physical laws which are far 

 from having been, up to this time, established upon certain bases. 

 The authors who have written upon the theory of these machines, 

 have been obliged to admit as the basis of their calculations, laws 

 which ought only to be considered as hypotheses to which physical 

 philosophers liave been led, most frequently, by extending to 

 vapours, laws which are not even rigorously exact for permanent 

 gases. Thus, when the work really done by a machine is com- 

 pared with that deduced from the theory, we always find, even in 

 the best machines, a considerable deficit. A great part of this 

 deficit may be attributed to the disturbances produced in the 

 physical conditions, by the very motion of the apparatus; it is 

 due to the loss of active force (force vivej occasioned by the 



* We are indebted 10 the " Fr.iukliD Journal" for the translutioii. 



cooling of the steam ; to the resistance which is developed during 

 its course through tubes of irregular forms, and in its passage 

 through openings, more or less contracted. Finally, there are 

 losses of active force produced by the friction and vibration of the 

 different pieces of which the machine is composed. But a great 

 part of the difl^erence may well be occasioned by the inaccuracy of 

 the fundamental lavvs w hich have been admitted into the calcula- 

 tion. 



Jlechanics have, for a long time, greatly desired a general in- 

 vestigation for the purpose of establishing these fundamental laws 

 upon a series of direct experiments executed with the means of 

 precision which physical sciences now present. I had for some 

 time formed the determination of devoting myself to this work, 

 and had several times tried some introductory experiments, which 

 however served only to show me that precise results could only 

 be obtained by means of large apparatus, whose expense of con- 

 struction far surpassed the verv narrow means which we have at 

 our disposition in our physical laboratories, and I should have 

 been comjiletely stojqicd in the execution of my projects, if the 

 Minister of Public Works (upon the suggestion of M. Legrand, 

 under Secretary of State), had not, with a kindness which will be 

 appreciated by all the friends of science, placed at my disposal the 

 funds necessary for the execution of this long and laborious work. 



In order to show clearly what are the principal laws upon wliich 

 the theory of steam-engines rests, it appears to me necessary to 

 explain, in a few words, the principles of this theory. All known 

 systems of steam-engines may be divided into four classes : 



1. Engines without expansion, and without condensation. 



2. Engines with expansion, and without condensation. 



3. Engines without expansion, but with condensation. 



4. Engines with both expansion and condensation. 



The first three classes, may, in a thecu-etic point of view, be 

 considered as particular cases of the fourth class, wliich presents 

 the most complex ease ; the only one to which it is necessary for 

 us to pay attention. We shall suppose an imaginary engine, 

 which is not sulijected to any external cause of cooling, nor to any 

 loss of active force by friction, contractions of orifices, <S:c, &c. 

 We shall suppose the boiler to be of very great capacity in com- 

 parison with the cylinder, so that tlie pressure of the steam may 

 be considered as absolvitely constant in the boiler during the motion 

 of the machine ; the heat of the furnace reproducing, constantly, 

 the quantity of steam consumed by the machine. 



Let a be the surface of the piston expressed in square metres*. 



•r, the space described hy tlie piston from the instant of the 

 arrival of the steam in the cylinder, with the tension which it 

 has in the boiler, until the moment at whicli we are examining it. 



P, the constant pressure of the steam in the boiler, expressed in 

 kilogrammes and referred to a square metre of surface. 



T, the temperature of the steam. 



r, the capacity, in cubic metres, of the part of the cylinders de- 

 scribed by the piston from its starting point to the height, ,r. 



V, the total capacity of the cylinder. 



I. A first law, which it is important for us to know, is the 

 law which connects the clastic forces with the temperatures. 



We will distinguisli two periods during the stroke of the piston: 

 during the first of these the cylinder communicates freely with 

 the boiler ; the total pressure of the steam upon the surface of 

 the piston is Poi. 



If the piston advances by a quantity dx, the element of work 

 produced wil be Vuid .r = P dr. 



The whole quantity of work produced during the first period, 

 that is, from the beginning of the motion of the piston until the 

 introduction of the steam is sto])])ed (corresponding to a capacity 

 V, described by the piston in the cylinder), is P V. 



During the second period, which is that of the expansion, no 

 more steam comes from the boiler, but the steam contained in the 

 cylinder continues to press upon the piston ; as this rises, the 

 steam occupies a larger space, its elastic force diminishes, and its 

 temperature is lowered by the absorption of latent heat during its 

 dilatation. 



Experiment has not decided what are the laws wliich govern 

 these variations ; but one id' the following cases must happen : 



First case. — The quantity of heat absorbed by a kilogramme of 

 liquid water at 0° (32° Fahrenheit) in passing into vapour (which, 

 for the sake of simplicity, we shall call the total heat of the steam), 

 is the same, whatever may be tlie jiressure, provided the vapour lie 

 at its maximum of density. If this law be exact, the steam will 



* In the following Translation ue have preseived the French units of length, weight, 

 and temperature. The metre is -W-;d inches. The IdlngranitnT 2 21'5 lb,, av. 



The degree ot the Ct ntigrnde thermometer, IH degrees Fahrenheit. 



To reduce Centigrade to Fahrenheit degrees, multiply them by It, divide ttie piodiKtl 

 by 5, an.l adil ol! degrees. 



