:2«8 



SCIENCE. 



[Vol. IV., No. 85. 



are used in its construction. Eacli of the three main 

 piers consists of four masonry columns, 70 feet in 

 diameter, upon rock or hard clay bottom, centred at 

 the corners of a rectangle 270 7 x 120'. The deepest 

 foundation will be 70' below low water, which makes 

 it HO' high, allowing 20 ; for the tide, and 20' more 

 above high water. Add to this 340', and we have 

 450' total height. There need only be added a cen- 

 tral observing-tower or flagstaff to make it the high- 

 est structure in the world. Attention is called to the 

 difference between Euglish and other contractors: 

 the former are "not much accustomed to pneumatic 

 appliances, other than an ordinary diving-dress, and 

 rarely resort to them." No use lias been made of 

 pneumatic apparatus already provided, but for the 

 deepest piers compressed air will doubtless have to be 

 used. The compression members of the bridge are 

 tubes formed of bent steel plates riveted together. 

 Compression joints are planed to fit, and forced 

 together before riveting; and holes for rivets are 

 drilled, not punched. The tension members are box- 

 girders riveted up. A large number of experiments 

 have been made to settle doubtful points, notably as 

 to wind pressure, regarding wbich reliable data were 

 wanting: in so large a bridge, the weight of trains is 

 of little importance as compared with that of the 

 structure and the pressure of the wind. As it must 

 be a problem of some difficulty, to join the members 

 of such a structure in a substantial and artistic man- 

 ner, it is to be regretted that the details of the joints 

 were not shown, and that no judgment can be 

 formed of their merits. Altogether, though the pro- 

 portions of the structure may not be pleasing, they 

 cannot fail to be imposing; and the truss principle 

 will hereby, as regards possible span, be placed for 

 the first time abreast of the suspension cable. 



The discussion participated in by Messrs. Hanna- 

 ford, Leavitt, Emery, and Webb, brought out the 

 relative costs per foot — £200, £160, and £75 — for 

 this, the Victoria, and the International bridges; the 

 latter two having only a single track. Steel was 

 stated to be cheaper than iron; and many questions 

 were asked as to the constitution, properties, etc., of 

 the steel used, to which there was no time for suit- 

 able reply. 



A paper on the Severn Tunnel Railway, by J. C. 

 Hawkshaw, naturally followed. This tunnel, com- 

 menced in 1873, and nearly completed, is four and 

 one-third miles long, and will save over two miles of 

 ferriage. It is a twenty-five-feet hole, lined with vit- 

 rified bricks made from the excavated material, and 

 laid in Portland cement. It passes principally through 

 marl and coal, full of fissures. At the lowest point 

 its roof is forty-five feet below the river-bottom, over 

 which flows the water sixty feet plus a tide of thirty- 

 six feet. To reach this depth we have slopes of over 

 one per one hundred. Much trouble has been caused 

 by water. In one instance the wells for miles round 

 were dried, and a river nearly disappeared ; at another, 

 a sixteen-foot hole broke through the river-bottom ; 

 in fact, there has been a succession of floodings and 

 eavings-in, and the work is a monument of persever- 

 ance. Pumps have been added until there are now 



eighteen, with a capacity of forty-six thousand gallons 

 per minute. There have also been radical alterations 

 of the original plan. When Sir John Hawkshaw was 

 appointed engineer in 1879, he lowered the whole tun- 

 nel fifteen feet, necessitating a new driftway. The 

 driftways were commenced from several shafts; and 

 there are now twelve shafts about fifteen feet diam- 

 eter and from seventy to two hundred and twenty 

 feet deep. Electric lights are now used, and com- 

 pressed air has been employed for drilling and venti- 

 lation, though now air is forced through the entire 

 distance by an eighteen-feet-diameter fan. The cost 

 of the work is not known, and it is difficult to believe 

 that much time and money might not have been saved 

 by employing, from the start, a properly planned pneu- 

 matic process ; indeed, the extra fifteen feet depth of 

 the tunnel below the river-bed would seem to be a 

 permanent disadvantage which might thus have been 

 avoided. 



Three railway papers followed. The first, by W. 

 K. Muir, on single-track railways, was a condensed 

 statement of the construction and method of operat- 

 ing a railway in America, where but a single track 

 can be afforded. General plans of stations and cross- 

 ings were given, and an infinite number of details 

 alluded to as necessary to safety,' comfort, and econ- 

 omy. The numbering of the hours from one to twen- 

 ty-four was advocated. Much was said upon modes 

 of signalling, and an improved signal-lamp described. 

 It was claimed that white and red signals were suf- 

 ficient, it being safer to exclude green. In the dis- 

 cussion it appeared that an economy is effected by 

 strengthening cars so that they can be loaded full: 

 formerly grain was carried two and a half feet deep, 

 now four is customary. The American method of 

 making up a time-card was explained, where the trains 

 are represented by threads stretched over a board 

 ruled one way for time, and the other way for dis- 

 tance. Mr. Preece spoke of the safety on railways: 

 the safest place in England is supposed to be a first- 

 class carriage between London and Edinburgh. The 

 president advocated running trains by telegraph from 

 a central station, there being absolute safety with but 

 one train on the track at a time. This caused refer- 

 ence to be made to a Paris incident, where an un- 

 usually long train, going round a loop, ran into its 

 own tail. Sir James Douglass spoke of the excellency 

 of American head-lights, and advocated a mechanical 

 signal-lamp to save time; to which was replied that 

 the American train-man was quick, and a wiggle or 

 two of his lamp was enough. 



Mr. J. H. Wilson's paper on American permanent 

 way referred more to the construction of the line, 

 forming therefore a complement to the last. The 

 qualities of a perfect track are good surface and 

 drainage, and straight or truly curved track, of ac- 

 curate width, well fastened and with tight joints. 

 American rails rest with broad flanges on wooden 

 ties; while English rails are reversible, and rest in 

 iron chairs, so that ties can be placed far apart. 

 Wooden ties, being plenty here, should be laid only 

 two feet apart. Engines weigh from forty to over 

 sixty tons. Detailed specifications for rails, etc., acf 



