18i0.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



251 



fig. 4 a section on the line c, n. a, is the cast-iron girder; b, b, the 

 bottom flanges; r, c, two wrought-iron bars inserted into the bot- 

 tom of the girder, at a small distance apart, and, at the centre of 

 each flange, they are slightly bevelled outwards on each side, so as 

 to be dovetailed, as it were, into the girder at those parts. The 

 wrought-iron bars are introduced in the process of casting the 

 girder; — such bars having been previously rolled into the required 

 sectional form, and well cleansed from oxide by heating them in a 

 furnace or otherwise. Fig. 5 is a cast-iron girder r/, strengthened 

 by a bar of wrought-iron e, whicli forms the bottom of the girder, 



Jig. 4. Fig. 3. Fig. 1. 



Fig. fi. Fig. 7. 



and connected to the upper part by a central ridge, of a dovetail 

 form in its cross section, and of an undulating form in the longi- 

 tudinal direction. Other modifications in the form of tlie wrouglit- 

 iron bars may be adopted. Figs. 6, and 7, sliovv how this com- 

 pound mode of construction may be adapted to railway-b.ars and 

 bearings where these are (as is now ordinarily the case) of great 

 weight: — c, c, are the cast-iron parts; and w, w, are the wrought- 

 iron parts. 



SILVERING OF GLASS. 



Thomas Dkayton, of Regent-street, practical chemist, for "im- 

 provements in the sUi'ering of c/Zass and other surfaces." — Granted 

 December 4., 18i8; Enrolled" June 4, 1849. 



The improvements relate to silvering glass, by precipitating 

 silver on the surface of glass, and causing it to adliere thereto, 

 without previously coating the sui'face with any kind of material, 

 in tiie following manner: — Take one ounce of hartshorn, or am- 

 monia, and add thereto, two ounces of nitrate of silver, three 

 ounces of water, and three ounces of spirit, preferring spirit of 

 wine for the purpose; mix the same together, and allow the mix- 

 ture to stand for three or four hours, and then iilter for use. 

 When the mixture is used, to one ounce of it add g^-ounce of 

 saccharine matter, previously dissolved in equal quantities of 

 water, and spirit of wine, say half a pint of each, preferring grape 

 sugar for the purpose, when it can be allowed two or three hours 

 to dissolve. This mixture is to be laid over the entire surface of 

 the glass, which is to be kept at a temperature of 160°. AVhen 

 the silver has become thoroughly dry, it is to be coated with 

 mastic varnish, which serves as a protection from friction. The 

 fluid is also well adapted for silvering the surface of metals. 



TUBULAR BRIDGES. 



An accovnt of the Construction of the Britannia and Conway Tubular 

 Bridges, with u complete history of their progress. By ^VII,LIAM 

 Faikbairn, C.E. London: Weale; Longman. 1849. Svo. pp. 

 291 ; 20 plates. 



Disputes respecting priority of scientific discovery are seldom 

 terminated satisfactorily or conclusively. Of all the more import- 

 ant instruments and methods which have given man new powers in 

 the domains of art and science, there is scarcely one for the inven- 

 tion of which there are not many claims to this day unsettled. 

 The tempting nature of the prize offered, and the congruity of the 

 thoughts of men of learning at particular epochs, render the suits 

 which arise in the Chancery of science numerous and complicated ; 

 while from the difficulty of discerning the hidden processes of the 

 mind, and the subtlety of the distinctions between absolute origin- 

 ality of thought and its numerous counterfeits, the cases are 

 always difficult to adjudicate. We know that large books have 

 been written expressly to discuss the question of the invention of 



the telescope. The antagonistic claims of Newton and Leibnitz 

 to the honour of devising the metliods of fluxions, gave rise to a 

 paper war which is not yet terminated. To come down to a period 

 within our immediate recollection — the ])rediction of the place and 

 motion of a new planet has raised to the highest scientific rank 

 two rival and independent discoverers. 



The controvei-sy to which the experimental and theoretical in- 

 quiries respecting Tubular Bridges have given rise, is on many 

 accounts to be regretted. The subject was eminently one which 

 required concurrence and unity of purpose among the investiga- 

 tors. They themselves are men who have one and all done good 

 ser\ice for science, — men who have been honourably associated for 

 years in the mutual pursuit of science, — men whose attainments 

 have won for them public respect and confidence. We have not 

 yet the whole evidence of the case before us, and feel it premature 

 to decide upon an e,v-parte statement. jAVe, moreover, arc anxious 

 to avoid pai'ticipating in a contest in which too much of the gall 

 and bitterness of jealousy has been exhibited. But we have 

 enough evidence at least to he quite certain that the discussion 

 has throughout been too strongly marked by the absence of mu- 

 tual concessions, and has been caused solely and entirely by feel- 

 ings of distrust, and a jealous concealment or reserve, which seem 

 absolutely incompatible with a pure love of science. 



They love science best, and are its most successful disciples, 

 who follow it for its own sake — not for the aggrandisement of 

 personal renown. We like not to see men too avaricious and 

 greedy over their scientific wealth, — hiding and hoarding every 

 morsel of truth which they can snatch unobserved. It is only the 

 miser who acts so. They who are really rich in intellectual trea- 

 sure, who possess the mines of exhaustless minds, are liberal 

 withal. The craven, who tremble for the little by which they are 

 richer than their neighbours, have but a pitiful store. There is 

 that scattereth and yet increascth; and there is that wittwUieth more 

 than is meet, but it tendeth to poverty. 



The present work does not very distinctly set before us the 

 exact nature of the claims which Air. Fairbairn prefers ; but we 

 believe the following may be fairly stated to be the principal re- 

 sults which he asserts to have been the fruits of his inquiries — 

 1st, tlie preference of a rectangular to a circular tube; 2nd, the 

 abandoimient of the suspension chains originally contemplated; 

 3rd, the cellular structure of the top of the tube; Uh, the hydrau- 

 lic lifting app.aratus. 



On the first question it seems unnecessary to enlarge, as it was 

 disposed of at a very early stage of the inquiry. It requires such 

 a very mild knowledge of mechanics to perceive, that of two uni- 

 form tubes of equal height and length, the rectangular must be 

 stronger than the circular for a given quantity of metal, that, 

 instead of assigning any merit for the settlement of the point, we 

 are rather disposed to wonder how it could have been ever doubted. 



On the other questions raised by Mr. Fairbairn, we shall for the 

 present content ourselves almost entirely with a mere condensed 

 narrative, in which it is to be understood tliat in general the au- 

 thority for disputed facts is the work before us. It is probable 

 that counter-statements will hereafter appear; but, until then, 

 sufficient data will not have been furnished for a decisive opinion 

 on the general merits of the case. 



The tubular Ijridges for the Conway and the Menai Straits ap- 

 pear to have been first proposed by Mr. Stephenson, about April 

 1845; and it is, happily, a point uncontroverted that the original 

 idea of substituting a rigid tube for bridges of the ordinary forms, 

 belongs exclusively to him. We are informed in the work before 

 us, that, at the time mentioned, a "consultation" with Mr. Fair- 

 bairn took place, at which Mr. Stephenson appeared to think that 

 "the tube should be either of a circular or egg-shaped sectional 

 form. He was sti'ongly impressed with the primary importance of 

 the use of chains, placing his reliance in them as the principal sup- 

 port of the bridge; and he never for a moment entertained the 



idea of making the tube self-supporting In fact, for several 



months afterwards, and even up to the time of the experiments on 

 the model tube, in December ] 840, he insisted, as will be seen from 

 the annexed correspondence, on the application of such chains." 



Of course, we are quite unable to contradict any statement made 

 by Mr. Fairbairn, of what took place at the consultation in ques- 

 tion. But we are prepared to contradict the assertion, that for 

 several months afterwards Mr. Stephenson insisted on the applica- 

 tion of chains. On the contrary, we have incontrovertible proof 

 that in the month following this consultation, he distinctly and 

 strongly urged the practicability of dispensing with the chains 

 altogether. 



From an authentic copy of the minutes of evidence of Mr. Ste- 

 phenson, on the 5th and 6th of May 1845, before the Committee 



33* 



