1841.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL 



123 



by the same construction gives 7" 3' 5" as the versed sine. Fide 

 Quarterly Journal of Science. 



I am, Sir, 

 Wooler, Your very obedient servant, 



2iith January. Expertus Loqui. 



Geometrical Solution. 

 Construction. — The span or chord AA being given, subilivide it 

 accurately into eight equal parts. Add to each extremity of the 

 chord AB also an equal part, the semi-diameter of the piers. Bisect 

 the extreme divisions of the chord AC in D, and with DA as a radius, 

 and D as a centre, describe the circle AEC. Then, from the centre 

 of the chord F to the point D as a dimension, make the equilateral 

 triangle FGD, and continue the line GD to E; — E is the point of inter- 

 section. Next, with CA as a radius and C as a centre, describe the 

 circle AH ; then take AF (one half the chord) as a radius, and G as 

 a centre, describe the arc EH — H is also a point of intersection. 

 Lastly take the base line BB as a dimension, and make the equilateral 

 triangle BIB, and with HI as a radius and I as a centre, describe the 

 arc HH, which gives the required curve. 



WOOLF'S DOUBLE CYLINDER ENGINE. 



Sir — An estimate has been given of the power of Woolf 's double 

 cylinder rotary engine, at page 50, February 184 1, — on assumed con- 

 ditions of steam pressure, so much at variance with those which could 

 occur, that I conceive further observations are required to elucidate 

 this subject. 



In regard to the Cornish engines, perhaps it would be difficult to 

 assign to each their relative position in the scale of merit, in the in- 

 troduction of the improvements by means of which so great an increase 

 of work has been obtained in Cornwall.l 



Woolf's advocates may fairly point to the reported duty of his en- 

 gines, which for a long period maintained their position at the head 

 of the best — at present neither his engines or boiler are in use. Trevi- 

 thick, who was equally well known as an advocate of high steam, went 

 to America just at the critical period when the results of the rivalry 

 established among the raining engineers had began to develop itseli. 

 His boilers still keep their ground, and have afforded other engineers 

 the means of working high steam expansively in Watt's engines, with 

 an effect far exceeding that as yet obtained from Woolf's engines. 



In the former the calculations for expansion are well known — but in 

 the latter the original volume of steam cut off is driven into another 

 cylinder during expansion — while the mean pressure of this steam re- 

 acts against the full pressure steam by which the smaller piston is 

 impelled. 



■The admission however of the steam into the small cylinder may 

 be cut off at any portion of the stroke, and worked expansively during 

 the remainder, and may then be further expanded in the large cylinder, 

 so that the assertion that "the capacity of the smaller cylinder natu- 

 rally determines the quantity of steam which the boiler must supply," 

 is untenable. 



The only safe assertion respecting the steam pressure in the cylinder 

 would be that it is lower than that in the boiler, and the difference 

 was only considerable, especially in Woolf's practise, from his opinion 

 in favour of wire-drawing high steam, and the small allowance of 

 steam room in his boilers. 



Supposing the safety-valve of a boiler loaded with 40 ft. per square 

 inch, it is not probable that the constant total pressure in the cylinder 

 would exceed 4U ft., including atmospheric — that is, \i-7i> + ■2r>-2.'> ft., 

 having a volume of about (5/0 for one of water. Had the steam been 

 expanded at 40 -j- 14'75 := o4J ft. the volume would have been 520 for 

 one. 



During expansion on the given conditions of the respective cylin- 

 ders, the mean pressure of the steam would be about 17 ft. per square 

 inch on the large jjiston, with a reaction of 17 ft. per square inch on 

 the smaller piston — against the pressure of 40 tb. full pressure steam 

 on the other side— hence 



3 ,, ... •207-39x40— 17 X 176-34 



Small cylinder — — = 2>-5 h. p. 



Large cylinder 



33,000 

 tiliO X 17 X 242 

 33,000 



Absolute power 

 Friction ^: i 



Effective power 



82-28 



107-78 

 35-92 



71-86 



Taking similar conditions of water evaporation, and cubic feet of 



steam required, we should have — ^ — = 25 cubic feet of water per 



0/0 



hour, and at 8 ft. of water from 1 ft. of coal, the consumption would 

 be about 2 ft. of coal per horse power per hour. 



Numerous causes might produce a consumption of ! or 4.4 ft. of coal 

 per hour, the difficulty wouhl be the reduction cif the coal expenditure 

 to the quantiti- theoretically calculated as sufficient. Instead of low 

 pressure engines, the proper standard for Woolf's, are Watt's engines 

 working high steam expansively, both using similar boilers and coal. 



I am not aware of any trials under these conditions, which can be 

 considered conclusive in regard to their relative merits. 

 I remain, vour obedient servant, 



March 11. " Y. 



CONSUMPTION OF COKE—GLOUCESTER AND BIRMING- 

 HAM RAILWAY. 



Sir — In Whishaw's Railways of Great Britain, page 30, there is a 

 statement taken from a paper by Capt. Moorsom relative to the per- 

 formance of a locomotive engine imported from the United States, 

 that in seven journeys of 5ilG miles up to Birmingham, the engine 

 conveyed 6S2 tons gross, and consumed 177 sacks of coke (1^ cwt. 

 each),' and in seven journeys of 59G miles down from Birmingham, the 

 same engine conveyed 629 tons gross, and also consumed 177 sscks of 

 coke. 



Mr. Whishaw observes, " Thus the consumption of coke, according 

 to this statement, taking the average of the loads up and down, was 

 at the rate of only -007 ft. per ton per mile 1 1 " 



The meaning of Capt. Moorsom's statement seems to be that the 

 engine passed over twice 5HiJ miles with a mean load of 93-64 tons, 

 and consequently her consumption would be -541 ft. of coke per ton 

 per mile. 



It may not be difficult to account for Mr. W.'s erroneous figures ; if 



682+629 

 2 ~ 



had been the mean load carried, the consumption would 



have been about -07 ; and a mistake in the position of the decimal is 

 not uncommon. I cannot account fur the two notes of admiration so 

 readily, as they prove that his attention was called to extraordinary 

 apparent economy of the consumption of coke. 



I remain. Sir, 

 March 11. Your obedient servant, 



Y. 



MONUMENT ERECTED AT LIMERICK TO THE MEMORY OF 

 THE LATE VERY REV. DR. HOGAN. 



We were yesterday favoured witli a view of the monument ju^t erected in 

 the parish chapel of St. Michael, to the memory of the late very excellent 

 and justly esteemed pastor ; and we freely acknowledge that, in classic 

 chasteness of style, correct architectural proportions and superior heauty of 

 execution, the monument surpasses any thing ot the kind heretofore seen in 

 this part of the country, and probably not infeiior in these qualities to any 

 other specimen of modern sculpture in the Kingdom. The appearance of 

 this memorial to departed worth is at once imposing and elegant, and the 

 eye loves to rest with pleasure on its sublimity of conception, the elaborate 

 beauty of its detail in the various compartments, and the superior finish of 

 the workmanship, from the most minute object to the most prominent, which 

 is a figure of the Archangel Michael. Well may the subscribers be proud of 

 such a lasting record of the virtues of him whom it commemorates, and 

 happy may the highly gifted and eminent artist feel, the production of whose 

 tasteand ability it is. Mr. Bardwell, of London, is that gentleman, and at 

 present engaged in the erection of that magnificent edifice, Gleustall Castle, 

 in this county. 



It is a mural monument, of Gothic architecture, at the period of the l.'ith 

 century, and the details are principally taken fi-oni the Chapel of Henry VIL, 

 in Westminster .Vbbey; also, from the Chapel of Magdalen College, Oxford. 

 The monument, which partakes somewhat of the character of a shrine, is 

 apparently borne aloft, or supported, by four angels, correctly copied from 

 the works of Waiufleet, Bishop of Winchester, and founder of Magdalen 

 College. One of the angels bears a shield, another a book, another a censer, 

 and the other a hly — this last, which is particularly beautiful and true to 

 nature, was a favourite emblem of Wainfleet's, ami figures in many parts of 

 Majdalen College. The design consists of three compartments, divided by 

 holdlv projecting buttresses terminating in richly crocketted finials, subdi- 

 vided' by rich and elaborate tracery into smaller ones. The whole design 

 may indeed be considered allegorical, consisting of a number of beautitid 

 figures, each having reference tothe spiritual duties and pious characteristics 



S 2 



