3G0 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[Deceubeb, 



resist. And the inference might be fairly drawn, that indications 

 of danger would be testified by less-important members of this 

 bridge than its suspension chains, before fears need be entertained 

 of their beiiij; uiiC(iual to their purpose. 



The conclusions we arrive at are these :^ 



1st. That when the bridge is fully loaded, the strain on the sus- 

 pension chains is i\ tons per square inch, or in the most extreme 

 ca.se 5 tons per square iiu^h, — being one-half the strain under which 

 iron is considered to he perfectly safe, and reserving cue-half its 

 power to meet contingencies. 



find. That 66 lb. ])er square foot of platform is sufBcient allow- 

 ance in estimating the weight of au accidental crowd of persons 

 upon suspension bridges. 



October 30th, 1848. J. II. 



[The above letter having been referred to the writer of the 

 '■ Notes on Engineering," he appends the following note :— 



The researches of "J. H." seem to prove satisfactorily that the 

 weight of Ilungerford Bridge has been over-estimated in the paper 

 {ante p. 292, Oct. ISIS) on the strength of that structure. In col- 

 lecting the data of that paper, considerable pains were taken to 

 reconcile the apparently contradictory accounts of the weight of 

 the bridge, given in the extract (vol. viii., p. 165.) from Mr. Cow- 

 per's paper, which contains the following words : — '' VVe have there- 

 tore, for the weight the bridge will actually bear, 290 X 171 tons =: 

 5,180 tons, while 296 X 5 tons = 1,1.80 tons is the greatest load thai 

 can be actually put uimii. it." — ^Vns it not natural to infer from this, 

 that Mr. Cowper had ascertained that the weight which the main 

 chains would have to sustain was 1,480 tons .'' 



However, the above letter shows that the words just quoted are 

 not the statement of an ascertained fact, but probably the infer- 

 ence from some theoretical computations not given. The main 

 chains of the central span consist of 1,280 links, of which each 

 weighs 5^ cwt., and therefore the whole together 352 tons. This 

 item, however, does not include the weight of the coupling-bolts, 

 pins, and suspension plates : with respect to these, and the weight 

 of the platform and parapet, which are massive and strengthened 

 by iron stays, we have no data. There are certainly no authentic 

 grounds for objection to the estimate of "J. H.," but in the ab- 

 sence of more certain information, the following seems a legitimate 

 mode of estimating the total weight of the structure. Mr. Cowper 

 remarks, that " the entire weight of the chain, platform, and full 

 load upon it would make a load of about 1,000 tons on each pier." 

 This gives 2,000 tons total weight of the whole bridge ; and as the 

 centre span is one-half the total length of the structure, it appears 

 safe to assume that the whole weight of the centre span, platform, 

 and load is 1,000 tons. This would make the horizontal tension 

 per square inch at the centre of the main chain ^6 tons. 



It must be remarked, that the words, " the present critical state 

 of Hungerford Bridge," are used by "J. H." on his own authority, 

 and are not to be found in the "Notes of Engineering." It was 

 not said, nor suggested in them, that Hungerford Bridge was in a 

 "critical condition ;" all that was asserted was that which admits 

 of strict proof— that, assuming certain apparently accurate data 

 for the weight and dimensions of the structure, the metal was 

 subject to a tension of 9 tons per squai'e inch. It now, however, 

 appears that the data themselves were incorrect, and that the 

 tension is consequently less; but even the greater amount would 

 by some practical men be deemed within the limits of security. 

 The error in question, which, respecting a point of fact, is not, how- 

 ever, to be regretted, as it has occasioned an inquiry and revision, of 

 which the results are by their near agreement recommended to gene- 

 ral confidence. Another benefit of the discussion has been, that it 

 has elicited on one side a display of interesting and extensive re- 

 search which, it is to be hoped, will be renewed in other investiga- 

 tions of that important class of which the above letter indicates 

 the familiar study.] 



The "Taman." — On Monday, the 13th ult., this iron steamer was launched 

 from the works of iMessis. llobinson and llussell, at MillwiU. She is 175 

 feet long, 2lj feet beam, and is to have engines of 180-horse power. Her 

 ^ines are by Mr. Ditchburn, and the hull is very smoothly finished. The 

 Taman is built for the Russian government, to be employed on the Black 

 Sea. She is to he handsomely fitted by Messrs. Paul. On the next slip is 

 an iron steamer for the Nabob Nazim, one of the mediatized princes of In dia. 

 She is to go fourteen miles an hour on the Ganges, and is to be used by the 

 nabob in his hunting trips. This shows the progress of European luxury in 

 the East, as the Taman proves that English skill is not yet surpassed on the 

 freezing sliores of the Black Sea. The nabob's steamer will make the 

 seventh built by Messrs. Robinson for the Ganges. An iron steamboat for 

 the Ilumber is to be laid down oa the slip of the Taman, 



CONTRIBUTIONS TO RAILWAY STATISTICS, 



In 184G, 1847, and 1848.— By Hvde Clarkk, Esq. 



(Concluded from potje ii&.J • 



No. XXIV.— MISCELLANEOUS GOODS. 



Among other articles enumerated in the returns, are furniture 

 and vitriol. 



In the year ending .SOtli June, 1846, there was carried on the 

 Manchester and Bolton, 256 tons or furniture; .on the South- 

 Western, 325 tons (half-year) ; and on the Brighton, 2,923 tons. 

 The receipts were, Manchester and Bolton 128/.; and Brighton 

 4,687/. 



In the year ending 30th June, 1847, there was carried on the 

 Brighton Railway 4,669 tons, the receipts for which were 6,660/. 



The carriage of furniture is now considerable, the railway being 

 preferred to the canal for long distances. The rates per ton per 

 mile are high. On the Manchester and Bolton the rate is 12-/. ; 

 on the London and South-Western, 7'26d. ; and on the London 

 and Brighton, 7-49(/. 



Vitriol is carried on the Newcastle and Carlisle Railway. In 

 the year ending 30th June, 1846, 17 tons, bringing 11/. ; and in 

 1847, 62 tons, bringing 39/. Vitriol is classed as dangerous, and 

 the rate for carrying it is 6^d. per ton per mile. 



No. XXV.— GOODS. 



The gross tonnage of goods in the years ending 30th June, 1844, 

 1845, 1846, and 1847, is as follows, including evez'y description of 



traffic: — 



