320 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



[OCTOBEB, 



inconslderaLle in the case before us. Also the expression for the 

 radius of curvature is in reality dependent on the varying ratio of 

 the tension to the extension. But that the re<il deflection of a tube 

 of the given dimensions, subject to the given weight, would be much 

 larger than the deflection given in the published accounts, appears 

 certain from this consideration: the strain would be more than IS^ 

 tons at the centre; and it would be larger for a considerable dis- 

 tance on either side the centre; conseijuently, the extension of the 

 material would be great, and therefore the radius of curvature 

 small, for a large portion of the curve; whereas the published 

 deflection would make the radius everywhere large. 



As it appears then from the evidence of practical men, and also 

 from the computation above, that it is quite impossible that the 

 tube could sustain anything like the computed tension, we are 

 driven to the conclusion that the data themselves are erroneous. 



^Ve refr.ain from comment on this most disagreeable conclusion, 

 for the charge which it involves is of too serious a n.iture to be 

 disposed of satisfactorily in an incidental manner. The public 

 were indubitably called upon to place confidence in the sufficiency 

 in the tubular bridges by the evidence of this very experiment, of 

 which the particulars, it is but too evident, have been wrongly 

 stated. We are anxious to believe that the exaggeration of the 

 strength of the model tube was unintentional, that it did not 

 arise from an ignorance of the power of mathematics to detect 

 the fallacy, or a futile hope to escape that irresistible cross-exa- 

 mination. 



Happily we have the investigation of Mr. Hodgkinson to give 

 confidence as to the strength of the actual Conway tube. Mr. 

 Tate objects that whereas in the tubular bridge the upper side of 

 the cells is more compressed than their lower part, that investiga- 

 tion proceeds on deductions from experiments in the direct longi- 

 tudinal compression of cells by a pressure uniformly distributed 

 over their ends. But the vveight of the objection is small when 

 it is considered that the ine(iuality of the pressure is small on 

 account of the comparatively great distance of the neutral axis. 

 The general character of Mr. Hodgkinson's investigation appeai-s 

 to be that of a careful and moderate estimate of the strength of 

 the Conway Bridge, which, if the complexity of the subject do not 

 permit of its perfect accuracy, is far, very far, more worthy of con- 

 fidence than any deductions from the Millwall "model tube." 



Useful Hints on Ventilation. By W. Walkee, Engineer. 

 Manchester: Parkes. ISoO. 



yVv. are glad to see from the numerous and cheap works which 

 issue from the press, that ventilation is attracting its fair share of 

 public attention, and we therefore welcome the present contribu- 

 tion, as no doubt our readers will; and although ventilation is 

 now supposed to be well enough understood, they will no doubt 

 read with satisfaction the extracts we here give, illustrative of Mr. 

 AValker's practical treatment of tlie subject. 



In reference to steam agency Mr. ^V'alker observes: — 

 '■However useful steam agency, as apjdiedto ventilating purposes, 

 may be in factories or buildings connected with them, and in theatres 

 or other places liable to great and sudden influx or efflux of persons; 

 and well as it has been found to answer in its application to other 

 buildings, such as club-houses, banks, collegiate institutions, and 

 hospitals, in which manifest advantages have been derived from its 

 employment; there will still be ^reat numbers and many classes of 

 edifices in which it would be, from various causes, inadmissible. 

 Churches, chapels, and houses for worship, may be enumerated 

 under this he.ad — the numbers contained within their walls being, 

 on the whole, tolerably constant, and not liable to very sudden 

 fluctuations; but especially from the circumstance that they are 

 seldom used more than two days in the week, with intervals of two 

 or three days between; and when used it is only for two hours 

 consecutively, with intervals of two or three hours between. ^V^ith 

 such proper quantity and sizes of ingress and egress flues as can 

 readily be obtained in the thick walls and piers of such edifices 

 (if planned prior to their construction), this short period of occu- 

 pation will not permit their atmosphere to become very highly 

 charged with impurities, while the intervals between the services 

 will be found sulficient for an entire change of the whole atmo- 

 sphere left in them at the close of each service, without resorting 

 to mechanical means. In churches with lofty open roofs, of the 

 mediaival or early-English construction, without galleries, the 

 total cubic space bears so large a proportion to that portion of it 

 occupied at the floor level by tlie congregation, that scarcely any 

 injurious vitiation _of the entire atmospheric contents can take 



place during the short period of occupation, provided moderate 

 prepar^itions have been made for ingress and egress. Hence, very 

 sudden and powerful ventilation is scarcely required in such 

 ehurclies, and the purification of their atmosphere may safely be 

 left to the spontaneous action of those preparations; but on spe- 

 cial occasions, and in hot weather, the action of the fresh-air 

 flues may be accelerated by the exhausting power of a shaft or 

 trunk of adequate size running up within the 

 tower or steeple, its upper end discharging into 

 the external air, while its lower end communi- 

 cates with the interior by openings in or near 

 the roof; and this shaft may be made, in very 

 hot weather, to perform two or three times its 

 usual duty, by rarifaction produced at its 

 lower end g by a large number of gas burners 

 fixed there in tolerably close proximity with 

 each other, and supplied with gas from the 

 mains which furnish light to the whole build- 

 ing. These ideas have been successfully car- 



F.„-. 1. 



nnnllnyniinf 



jl_i 



ried out in numerous instances and in large buildings. The whole 

 process recommended for such a buUding will be better undei'stood 

 by a reference to the upper portion of figure 1, which represents 

 a section of a church ventilated in this manner, a o, are openings 

 all round the church for admission of fresh air; b ?/, hot- water pipes, 

 over which it is made to pass on its way to the gratings c c; d d, 

 are openings, by which the vitiated air enters a horizontal trunk e, 

 from the end of which rises the shaft /, with a collection g, of 

 gas-jets in the bottom of it; h i, is the gallery-line, and k, an exca- 

 vated room for the boiler, the floor of which should be five feet 

 below the floor-line of the church. 



" By simply turning the cock in the gas pipe which supplies the 

 jets, tiie rarefaction in the shaft, and, consequently, the velocity 

 and quantity of the air passed through the church, may be con- 

 trolled with tiderable accuracy, and instantly proportioned to any 

 greater or smaller number of persons assembled. The cost of 

 piping and cock for bringing the gas to the jets has been found to 

 be bill trifling; and as they need only be lighted during the time 

 the church is occujiied for worship, which is seldom of longer 

 duration than two hours and a-half, the consumption of gas is not 

 very great, and amply compensated by the beneficial result 

 obtained. 



" The means most proper to be adopted for the plentiful supply of 

 fresh air in the low-roofed, galleried, and crowded meeting-house, 

 will be fouiul to consist in abundance of fresh-air openings all 

 round under the windows, communicating by brick flues with the 

 lower part of the spaces under the aisles and seats in which the 

 hot-water pii>es that are to warm the air should be fixed. Fresh- 

 air flues sliould be constructed in all the piers between the windows, 

 running as high as the gallery to supply it with fresh warmed air. 

 A vitiated air-flue should also commence in each pier under the 

 gallery (in order to give free egress to that which would otherwise 

 be intercepted and detained under the gallery), and pass up into a 

 horizontal trunk, running over the roof, along each side, into the 

 foot of the upriglit sliaft below the gas-jets, as before explained. 

 Openings should also be left in the roof, communicating with these 

 horizontal trunks, to carry off the bad and heated air over the 

 galleries. Hot water pipes should be conveyed along the side- 

 walls, under the floor, so as to warm the air that passes up within 

 the jiiers into the gallery. 



" The leading points to be observed in such a case are delineated 

 in the lower part of fig. 1, below the line h i. 



'•A much larger provision should be made for supplying fresh air 



