1842.] 



THE CIVIL ENGINEER AND AIlCillTECT'S JOURNAL. 



2S9 



for fear of its cracking;, in consequence of tlie moisture being removed from 

 the outside before the interior of the block can have had time to evaporate; 

 hence, while the central part remains of its original size and extremely damp, 

 the surface will dry, shrink, and thereby cause many invisible cracks, tlie 

 effect of which will be conspicuous after a sharp frost. 



" All free-working limestones and oolites become in some degree harder 

 on their surface by exposure to weather. This arises from a very slight de- 

 composition taking place, which will remove most of the softer particles, and 

 leave the hardest and most durable to act as a protection to the remainder. 

 In addition to which, the pores and interstices of t;:e surface fet filled with 

 dust and dirt, washed in by rain assisted by powerful winds ; all which cir- 

 cumstances help to secure the least protected grains from external violence. 

 If the stone be naturally compact and durable, a surface of tbis description 

 ■will materially assist its' duration ; but, on the other hand, such material as 

 the Ileddington stone, near Oxford, or the most peris' able Bath stone, will 

 in due time" similarly attain a hard crust, which, from tiie general body of the 

 stone being loose and powdery, is not sufficiently compact to hold on ; water 

 will soak in behind the crust, cause a swelling and disruption on the surface, 

 ■which ultimately breaks. The crust thus opened gradually bends forward 

 more and more, until finally the weight of the disintegrated portion causes it 

 to fall off. In some instances, as in Bath stone, these defective places rarely 

 exceed an inch or two of surface before the decomposed part falls off; 

 whereas the crust of the buildings at Oxford is so remarkably tenacious that 

 it peels off and hangs like rags, often as much as a foot superficial, before it 

 entirely separates. Upon tlie' whole, I do not consider it a recommendation 

 to a soft stone to say that it gradually becomes harder on the surface." 



We must fake leave of this paper, from which we are tempted to 

 continue our extracts to a greater leiigtii than might be advisable. It 

 is illustrated bv a map of the Island of Portland, and a. section of the 

 strata from which the stone is raised. It concludes with some obser- 

 vations on M. Brard's process for testing the qualities of building 

 stone by disintegration, which Mr. Smith holds rather clieap, -as not 

 being supported by established physical truths, tliat is to say, by the 

 effects observed to have taken place in the same kinds oi stone by 

 long exposure in old buildings — Barnack stor.e, for example, which 

 remains generallv in the highest state of preservation in Peterborough 

 Cathedral, and other buildings in the neighbourhood of the quarries, 

 disintegrates rapidlv under the process, while others which stand high 

 for durability under this test, are found to have suffered severely from 

 the slow tooth of age. 



To Mr. Fowler's paper "On warming and ventilating the long room 

 of the Custom House, London, upon Dr. Arnott's principle," we have 

 but little to say. The practical application of a familiar principle is 

 precisely one of those subjects best calculated to occupy profitably the 

 time and attention of an evening meeting, and had we experienced 

 the pleasure of hearing this paper read on such an occasion, we could 

 have complimented the honorary secretary very sincerely on his pro- 

 duction. But for its place among the transactions it has probably 

 been indebted to its illustrations, which exhibit the only specimen of 

 original design with which the Institute have favoured us. The 

 composition in the second plate being quite unconnected with the 

 practical part of the subject, it is to be presumed, from the extra- 

 ordinary distinction with which it is treated, that the Society are 

 proud of it. We must confess we would rather the same breadth of 

 copper had been bestowed upon Herr Kallmann; but this, as the 

 upholsterers say, is a mere matter of taste, and we hint an opinion 

 upon it with extreme diffidence. 



The concluding paper is a report on the construction of the stone 

 arch, (or, according to popular designation, " stone beam,") which 

 exists between the western towers of Lincoln Cathedral, by Mr. 

 Nicholson, accompanied by an engraving, made from very careful 

 measurements. This arch, which is an object of curiosity from its 

 extraordinary flatness and lightness, consists of 23 stones of unequal 

 lengths. The width of the extrados is barely 1 ft. 9J in. ; the thick- 

 ness of the arch is uniform throughout, and is II in. ; the span 27 ft. 

 11 in. between the apparent abutments, but as the walls on both sides 

 have been cased since the arch was built, the original span is 30 ft. 

 The arch having settled into a somewhat irregular shape, doubts have 

 arisen as to the nature of the curve ; but Mr. Nicholson's minute 

 investigation decides it to be a pointed arch, drawn from two centres, 

 the chord of the southern arc being 13 ft. ll-6(;4 in., and its versed 

 sine 2-J-J in. ; and the chord of the northern arc 14 ft. 0-234 in., and 

 the versed sine 2i in. 



The object for which this singular structure was erected is a 

 mystery, and Mr. Nicholson considers it in vain to orter any 

 conjecture as to its purpose. Mr. Papworth, however, suggests in a 

 postscript, that it might have been set up at the time when the vaulting 

 of the nave was built, as a fixed point from whence levels and mea- 

 surements might be taken. 



We now conclude our lengthened notice of this volume, ■with an 

 earnest hope that the Institute may speedily be ia condition to lay 



before the public another, equally instructive, entertaining, and orna- 

 mental. We can bestow upon them, at parting, no better wish. 



j^j.jxiidix D lo the new edition of Tredgold on the Sleam Engine and 

 on Sleam Naviaalion. On tlie ^ichimidfan Screff, or Submarine 

 Proptlltr. By Elijah Galloway, Civil Engineer. London: John 

 Weale, 59, High Holborn. 1842. 



This is a work which does Mr. Galloway great credit, and which, 

 we venture to predict, will be received by engineers most favourably. 

 The subject is itself one of great interest, and Mr. G I'loway has 

 treated it in a very perspicuous and business-like manner. He evidently 

 understands what he talks about — has studied it deeply and well — and 

 has the art, moreover, of stating what he knows in clear, concise, and 

 not inelegant language. Our inquisitorial office would speedily become 

 a sinecure, if we had none other than such books ss this to deal with. 



Mr. Galloway first gives us a short historical account of the Archi- 

 medean screw as a propeller, from which we extract the following 

 passages : — 



" In a work on the theory of the screw of Archimedes, published 

 at Paris in 17G8, by M. Paucton, the following passages occur : — 



' The oar is an instrument by means of which we are enabled to move a 

 vessel on the surface of the water. It is a long lever, terminated by a flat 

 end, by the pressure of which upon the fluid an operation similar to the 

 action of a wedge upon wood is produced. The imint d'appui of this lever 

 is the pin to which it is attached ; the moving power is the rower; and the 

 resistance is the fluid : which is, however, contrary to the opinion of some 

 writers. I am surprised that no one has thought of changing the form of 

 the common oar, it being evident that it is not perfection. In effect, besides 

 that the action of the rower is not calculated to make the vessel advance 

 equably, because the oars descrihe arcs of circles in their movement, the 

 Tovtev is obliged at least to employ a moiety of his time and strength to Uft 

 the oar out of the water, and carry it in advance. To remedy this incon- 

 venience, it would be necessary to substitute for the ordinary oar an instru- 

 ment the application of which would be if possible uniform and continuous ; 

 and this property will, I think, be found in perfection in the pternphore (the 

 Archimedean screw). We should be able to place two of them horizontally 

 and parallel to the vessel's length, one on each side, or one only at the fore 

 part. The pterophore may be entirely immerged, or up to the axis only, as 

 is desirable. The size of the pterophore will depend on that of the vessel, 

 and the curvature of the thread on the velocity with wliich it is proposed 

 to row.' " 



This is, perhaps, one of the earliest notices of the screw as aa 

 instrument of propulsion since tlie revival of learning, but it appears 

 to have been in use among the Chinese for that purpose from time 

 immemorial. Some of the schemes of propelling by means of a screw, 

 which drew the public attention about thirty or forty years ago, were 

 simply importations from China. Mr. Galloway quotes some certifi- 

 cates, with tlie view of showing that the screw had been introduced 

 in some of our Government vessels as an auxiliary means of propulsion 

 as early as 1802, and that the models of the plans then adopted were 

 subsequently examined and approved of by Mr. David Napier — than 

 whom there are few better judges in all such matters. He then reca- 

 pitulates the statements of Marestier in his work on American steam 

 navigation; the projects of Brown, the inventor of the gas vacuum 

 absurdity ; and the speculations of Tredgold, which are shown to be 

 in many respects erroneous; after v/hich he comes to the era created 

 by the achievements of Mr. Smith, to whom, we conceive, any success 

 this mode of propulsion has realized is mainly attributable. The 

 structure and performance of the Archimedes are next minutely 

 described : with these details many of our readers are already con- 

 versant ; and those who are not so we must refer to Mr. Galloway's 

 work, as no abstract would be useful, and no abridgment would be 

 right. Of Ericcson's propeller, shown in Figs. 1 and 2, we think 

 favourably; and Mr. Rennie's modification of the screw, repiesented 

 in Fig. 3, is certainly very ingenious. Hunt's propeller is also inge- 

 nious, though in its present state attended with many obvious incoii- 

 veniencies. Capt. Carpenter's plan is a crudity, and is scarce anything 

 more than a reproduction of one of Shorter's worst projects. 



On the mode of communicating motion from the engine to the 

 screw, Mr. Galloway makes some very judicious observations. The 

 instruments for modifying motion are toothed wheels, straps or ropes, 

 and fiiction surfaces ; and as the screw has to move at a much greater 

 velocity than the engine, the adoption of one or other of these agents 

 is indispensable. Toothed wheels are very noisy, occasion consider- 

 able loss of power from friction, and are very susceptible of injury; 

 friction straps are liable to stretch and slip, especially when subjected 

 to the influences of heat, sail water, and steam ; and friction surfaces 



