294 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[Sept. 



2. The Victoria or ^ssemily Hall, Castle Hill, was designed by 

 James Gillespie Graham, Esq., Arcliitecf. 



3. The Debtors' Prison, on the C;ilton Hill, by T. Brown, Esq., 

 Superintendent of Pnblic Works, Edinbiirgli. 



4. Ti:t Phjsiciaiis' Hall, Queen Street, by Thomas Haiiilton, 

 Esq., Architect, and the three colossal figures of Hygeia, Esculapius 

 Hippocrates in front of it were sculptured by Alexander Ritchie, 

 Esq. 



5. The Commercial Bank, in George Street, by David Rhind, Esq., 

 Architect, and the sculptures in the pediment are cutting by Alex- 

 ander Ritchie, Esq. 



6. Donaldson's Hospital, to the west of the City, by W. H. Play- 

 tair, Esq., Architect. 



7. Htrtot's School, Rose Street, is understood to be by Alexander 

 Black, Esq., Architect. 



I am. Sir, yonr's truly, 



James Tod, Secretary, 

 Royal Scottish Society of Arts. 

 *** We have to return our best thanks for this letter, and will not 

 lose this or any other opportunity of urging upon our readers how 

 much they increase the value to themselves of this Journal by contri« 

 buting local information. We have no lack of letters propounding 

 theoiies, but there is sad dearth of tliose which contribute facts. 



WECIIAKICAL PROPERTIES OF AIR AND STEAM. 



We are gratified to find that we have succeeded in calling attention 

 to the loss of power in atmospheric traction by preliminary exhaustion. 

 The following letters suggest that the loss may be avoided by the use 

 of double-acting pumps. We think that by this means the loss is 

 diminished, though to what extent can only be ascertained by a separate 

 investigation, which, as the method of double-acting pumps is that 

 actually employed in practice, we will endeavour to give next month. 



Sir, — As there seems to he much in the article signed II. C. on the Pro- 

 perties of Air as applied to the Atmospheric Railway, which is calculated to 

 mislead those who are not in the habit of judging for themselves, but take 

 everything for granted which appears in a Journal like that of the " Civil 

 Engineer," I thought it would not be amiss to make a few remarks upon it. 

 I will leave all that part of it which views it histarically, and attempts to 

 draw a parallel between the modern atmospheric railway and the contrivance 

 of Papin, which as a means of conveying motive power to distant places 

 could scarcely he equalled for absurdity. 



The writer next attempts to prove that the partial exhaustion of the pipe 

 before the starting of the train contributes nothing to its motion, and that 

 is where the writer is so greatly in error, which to prove I will suppose that 

 the previous exhaustion has reduced the air in the pipe to a pressure of five 

 pounds on the inch, and that the cylinder of the pump is of the same dia- 

 Uieter as the long pipe in which the travelling piston moves, and that the 

 pump piston moves with the same velocity as the train; then, as the pump 

 piston is working against a pressure of fifteen with five in its favour, the dif- 

 ference being ten for the power required to work the pump, and the travel- 

 ling piston is moving against a pressure of five with fifteen in its favour, the 

 difference giving a tractive force of ten, there will be that equality between 

 the prime mover and the effect produced which the writer contends for, but 

 if he would only consider, he might see that when the pump piston has 

 finished its stroke the air within the pump cylinder has a pressure of only 

 five pounds to the inch, and consequently the jjump piston has a pressure on 

 its underside of only five pounds to the inch, while its upper side has a pres- 

 sure of fifteen, the difference being ten, which would diminish to seven and 

 a half when it had made a third of its backward stroke, to five when it had 

 made half, and to nothiug when it had made two-thirds, the air within the 

 cylinder being then at a pressure of fifteen. And that it would not require 

 any " omnipotent Act of Parliament" or " great monied interest," and but a 

 small share of the " mechanical genius" of the country to avail ourselves of 

 that pressure and to apply it either in working a double pump, each cylinder 

 of which would thus alternately assist the other, or in comumiiicating mo- 

 tion to a fly wheel which in its turn would give back the power (except what 

 was lost by friction and other mechanical defects) in assisting the pump in 

 its next stroke. And therefore it follows that if this pressure be applied 

 that equality which the writer contends for is destroyed, and that the pre- 

 liminary exhaustion cither does or may be made to contribute to the motion 

 of the train. 



A ^YORKING MECHANIC. 



2Veivcastle-uj!07i- Tijne, 

 July 28, 1845. 



*:i<* If our correspondent be a working mechanic, in the ordinary 

 acceptation of the phrase, his letter does him great credit indeed. 

 He will find the cases of the double-pump and of the pump working 

 with a fiy.whe<a fully discussed in the next number of this work, in thg 



Notes on the Philosophy of Engineering. We have received another 

 able letter on the same subject, but as the first part of it is almost 

 identical with the preceding, the writer will, we trust, excuse the 

 omission of it. The following passages on the effect of steam used 

 expansively put forth views which are for the most part correct 

 enough, and which certainly have not been controverted in this work. 

 The writer is not, however, quite justified in assumingthat if the 

 steam be cut off at the \ stroke the consumption would be reduced to 

 one quarter, as be may see by turning to the paper on the Lead of the 

 Slide. He will perhaps liave the goodness to read that article care- 

 fully, and if lie have any difficulties on the subject to write again. 



The writer next speaks of your previous correspondent's 



distinction between the " mechanical eflect of steam" and the power of a 

 steam engine in relation to Cornish (or expansion) engines, wherein, as your 

 correspondent says, " you may increase the mechanical effect of a certain 

 weight of steam by the very same operation that diminishes thepower of the 

 engine," and the writer does not '• know what private interpretation your 

 correspondent gives to the term " mechanical effect." 



Allow me to say how I understand the matter. A given weight of steam 

 at a given temperature is capaljlo, in the act of expansion, of exerting a cer- 

 tain amount of mechanical pov.er ; and as much of this power as is, in any 

 case, rendered available to our purposes, is termed the " mechanical effect" 

 of this quantity of steam, for while no engine whatever collects anything near 

 the n-hole of the power possessed by the steam, one engine may and does 

 collect a much larger fraction of this power than does another ; nay, the 

 same engine being used expansively will collect much more of the power of a 

 given quantity of steam than it would otherwise collect. In illustration, 

 suppose a certain steam engine has 100 h. p. while used !(«cxpansive!y, and 

 of course consuming a full cylinder of steam at each stroke of the piston, 

 whether upward or downwaid, now let the sam.e engine be used expansively 

 by cutting off the steam at } stroke, the consumption of steam would evi- 

 dently fall to one quarter only of the former quantity, while the power of 

 the engine would probably not fall below that of 60 horses. If this be cor- 

 rect, it follows that, the introduction, so far, of the expansion plan, as com- 

 pared with the non-expansion plan, utilises, as the French say, more of the 

 theoretic powerof the steam, and this in the proportionof GO to 25, and, other 

 l/ihiys e/jnat, is in that proportion more economical, for 2a per cent, of the 

 former quantity of steam is thereby made to yield 60 per cent, of the former 

 quantity of power. Also, " the m.echanical eftect cf a given quantity of 

 steam is increased by means which diminish the power of the particular 

 engine," because while the engine m.akes much better use of what steam it 

 does consume, the quantity of steam which it will receive is disproportion- 

 ately small. From this it follows that the highly economical use of the steam 

 requires a steam engine large in comparison with the [lowcr obtained, so that 

 it is always a practical question whetiier to submit on the one hand to a large 

 original outlay in the construction of the steam engine, or on the other hand 

 to a wasteful consumption of coals. 



E. H. 



NEW BUILDINGS IN LINCOLN'S INN. 



(From the Alhenaum.) 



In addition to its own intrinsic merit, the new structure, containing Hall 

 and Library, is so happily situated as to form one of the most conspicuously 

 placed architectural objects in the metropolis ; one that shows itself advan- 

 tageously from every point of view, and from whose windows a most enviable 

 rus-in-urlie prospect may be enjoyed of ' trim garden,' hounded by the hand- 

 some range r.f Stone Buildings on one side and of the park-like enclosure of 

 Lincoln's Inn Fields on the other. \Yliat adds not a little toils nobleness of 

 appearance is, that the new building stands upon a raised terrace ; which is 

 attended with this further advantage, that the basement floor is sunk only a 

 very few feet lower than the general level of the ground ; and what shows 

 itself externally as a basement for the oflices is a low ground floor, or mezza- 

 nine, between them and the Hall and other upper rooms. So well is the 

 building laid out, that although regular and even symmetrical in plan in the 

 direction of its length, the exterior is marked by great variety of outUne. 

 at the same time free from any little finical tricks of the picturesque; it being 

 thrown into well contrasted and well balanced masses, as is naturally dic- 

 tated by the disposition of the principal parts of the interior. We have here 

 that kind of grouping which is one distinctive characteristic of the style 

 itself — at least of the class of buildings which aflford the best examples of 

 the style, namely, collegiate ones. Mr. Barry would probably have treated 

 the subject difterently — would have shown us singleness of composition in 

 one continuous line of building from end to end, with very little external 

 articulation of the plan ; nor do we pretend to say that such treatment would 

 have been unsuccessful in his hands. Still we are well content with what 

 we here behold ; and are of opinion that the placing the Library transversely 

 to, instead of in continuation of, the main line of building, is highly favour- 

 able, not only occasioning a certain piquantuess of ensemble, but also giving 

 the extent in regard to depth. From tliis circumstance the building acquires 

 considerable impoitance as seen obliquely in a north-west \iew of it, which 



