1845.] 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



240 



passion"! miiat bond under tlie yoke of the Cross. The dove and the 

 lamb, which we frequentlv fiiid in the frescoes, on the catacombs, 

 and on the ancient sarcophagi, may signify, that as virtue arises Jrom 

 the Cross so vice is overthrown by it. 



We have already described several designs where a figure of Jesus 

 Christ surrounded by a glory, either elliptical or circular, is accom- 

 panied by the attributes of the four Evangelists. Christ is also re- 

 presented by his Cross, and the Evangelists by their Gospels; not 

 onlv is the Cross accompanied by signs and ornaments, but it is also 

 interlaced by them so to speak. The monogram of Christ, the Chi 

 (X), and the Rho (P) of XpiaTos, the Iota (I) of iriaovs, uniting form the 

 Greek and Roman Cross and stars with six equal or unequal parts ; 

 these Crosses are simple or enclosed in circular medallions, and are 

 sometimes square. In the next illustration composed of six cyphers 

 the Chi is in the St. Andrew's Cross. In the first five figures the Rho 

 cuts the Chi vertically, at the point in which the two branches are 

 intersected; we have thus the two first letters of XPI2T02. The 

 cyphers of No. 2, 3 and 4 are simple or open, and the No. 3 is com- 

 posed only of X and of p; No. 2 is accompanied by palms, which pro- 



things; Xo. 5 is inclosed in a medallion, but the r.iys of this niyslic.U 

 wlu-rl touch the circumference and mingle in it, wliile tliose of N'>. ti 

 do not touch it. This last figure does not present a Rho but an luli!, 

 which is the first letter of the Greek word IH20T2, as the Chi is the 

 first letter of XPI2r02. The sixth cypher is tln-n the most complete. 

 There is yet a vast number of inscriptions and allegorical orn inicnts 

 besides those which accompany the sign of the Cross and detail its 

 ficts and significations; but we have been compelled to confine our- 

 selves to the more essential points of this important subject. 



REMARKS ON THE MATHEMATICAL PRINCIPLES OF MR. 

 DREDGE'S PATENT SUSPENSION BRIDGE. 



By F. Bashforth, B.A., Fellow of Si. John's College, Cambridge, and 

 Member of the Cambridge Philosophical Society, 



" The constant destruction of bridges so fatal to life and property, arises 

 solely from the erroneous principles upon which they are constructed." — 

 Mr. Dredge's Advertisement. 



The recent fatal catastrophe -xi Yarmouth renders it imperative on 

 all persons to make use of every means in their power to guard against 

 the recurrence of a similar event. It is to me a matter of surprise 

 tliat there has been no exposure of what Mr. Dredge calls his " System 

 mathematically demonstrated, showing, by the most searching inves- 

 tigation, the true principles of the novel and economical invention." 1! 



In the work on Bridges, published by Mr. Weale, we have a Sup- 

 plement of G4 pages of demonstration, illustration, and examples. In 

 vol. xxxviii. of the Mechanics Magazine we have the " Mathematical 

 Demonstration of the Principles of Dredge's Patent Iron Bridges. By 

 the Inventor." In addition to these Mr. Dredge has printed for dis- 

 tribution anumberof letters extracted from newspapers, &c., explaining 

 in glowing colours the advantages in strength and cheapness of his 

 bridge. But most unfortunately not one of the writers even pro/emcs 

 to have any knowledge of mathematics, and consequently all their 

 opinions are worthless. In one of Mr. Dredge's advertisements we are 

 informed that " in such a structure as the Menai Bridge it (the patent 

 bridge) eiTects a saving of 1865 tons of iron in the main chains alone," 

 and in a note we are told that the "Menai chains leeigh 193.) tons." 

 We will now compare this with the statement in Mr. Page's Report, 

 printed by order of the House of Commons, May 9, 1844, page 2 1, and 

 reprinted in Weale's Quarterly Papers, Part V. page 20. "The 

 weight of the bridge (including 130 tons additional weight due to re- 

 pairs in 1839 and 1840) is 774 tons" ! In Mr. Proves' work we have 

 a similar statement. Again, we are informed that the " tension of the 

 chain must be nearly 3750 tons, half of it acting in each direction." 

 Did Mr. Dredge ever know such a method of measuring tension before 

 made use of? I compare this with another of Mr. Dredge's circulat- 

 ing letters, written by Lord Western to Lord Melbourne, which states 

 thataccordingtoDrewry"thestrain at the middle is 1875 tons." I make 

 no remark, — I have merely collected statements, and I leave the world 

 to judge. 



To proceed to the mathematical demonstration. — 



These are copies of figs. G and 8 alluded to below. In both figures 



Fig. 8. 



Fig. 6. 



bably signify triumph and glory ; No. 4 like No. 1 is completed by 

 the A and a, which signify that Christ is the beginning and end of all 



the same letters refer to the same. The pulleys E and B, fig. 6, are 

 supposed to turn about fijed axes, and a„ a„, denote the tensions of 

 the strings C E, H B, attached to the platform at C, H, and passing 

 over the pullies E, B; P F is the pier, P A a chain passing from the 

 top of the pier. Let 



F H B = ,^„, F C E = ,>>,... .F A P =: ,f.n 

 FH = rf„, ¥C = d,.... FA = rf„ 

 « the weight to be supported at G, G F = S. 

 6, — tension of A P. 



33 



