242 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



[July, 



EXPERIMENTS ON FOUR WHEELED ENGINES. 



All experiment has recently been made on the London and Birmingham 

 Railway, to show the safety of four wheeled engines when the fore-axle is 

 broken ; for this purpose the fore-axle of a four wheeled engine was cut nearly 

 through, and in tliis state, was sent from the station towards Koade; the fore- 

 axle broke in two as intended, at the point where it had been dividtd, hut 

 the occurrence had no apparent effect on the movement of the engine, which 

 continued its course till it reached Roade, when it was crossed from the 

 down to the up line, and returned in safety to Wolverton. On the following 

 day, the engine in precisely the same state started from WoKerton, with six 

 wagons of wheels and axles — making a gross load of thirty-two tons, exclu- 

 sive of engine and tender. With this load the engine attained a speed of 

 twenty-five miles per hour, and arrived safely at the Watford Station, distant 

 thirty-fo\ir miles. Soon after leaving Watford, and when it was again running 

 at a speed of twenty-five miles per hour, one of the front wheels slipped off 

 the rails, and the engine was delayed seven minutes until it was replaced. 

 The engine again proceeded towards London, but at about two miles beyond 

 the Harrow Station, where the line is on transverse sleepers, the wheels once 

 more slipped off the rails, and the engine, in that state, ran npwards of 200 

 yards before it was stopped. In twenty minutes it was again lifted on to the 

 rails, and started to Camden Town, where it arrived in safety before live 

 o'clock. 



[The experiment is reported to be " highly satisfactory." Forourowu part 

 we cannot see what there is to make it so ** highly safiftfactnry ;" we view the 

 experiment in a very different light : what more serious evil can there be than 

 an engine running off the rails as in the above case ? Imagine an engine twice 

 off the rails within the distance of ten miles ! Suppose a similar accident had 

 occurred with any other engine and train, would the tools and the men have 

 been ready to replace the engine upon the rails within ten or twenty minutes 

 after the accident had happened .' and would the same precautions have been 

 taken and the same look-out for the avoidance of accident ? Let lis hear of 

 no more such mad-hrainen, hair-breadth experiments ; this one is quite 

 enough.] 



THE VARIATION OF THE COMPASS. 



Observations made at the Royal Observatory, Greenwich, 

 G. B. AiRv, Astronomer Royal. 



PROCEEDINGS OF SCIENTIFIC SOCIETIES. 



INSTITUTION OF CIVIL ENGINEERS. 



March 15. — The President in the Chair. 



" Sesvriplion of the Iron Siew Bridge across the Regent's Canal, on the 

 Eastern Coiinties Railway." By Edward Dobson, Assoc. Inst. C.E. 



This bridge is built with a direct span of .^)4 ft,, at an angle of 79° with 

 the centre line of the canal. The level of the rails is 1 1 ft. 6 in. above the 

 water, and it is constructed to have a water-way of 4 4 ft., with a clear head- 

 way of 10 ft. above the towing-path. 



The dimensions of the severaj parts of the bridge and the mode of putting 

 tbem together, with the masonry and the cost of the construction, are de- 

 scribed in detail, and illustrated by an elaborate working drawing. 



As an appendix to this paper a description is given of a bridge over the 

 same canal, on the line of the London and Birmingham Railway, on account 

 of the similarity of its construction. The span of this latter bridge is 

 50 ft., but being made for two double lines of rails, it was thought expedient 

 to have three main ribs instead of two, as in the former. The details of 

 construction of this bridge are also given, with a drawing of one of the main 

 ribs and its tie-bar. 



" Remarks on the Ravages of the Worm (Teredo NavalisJ in Timber." 

 By Robert Davison, M. Inst. C.E. 



This communication describes the ravages committed by the " Teredo 



Navalis" upon the fir piles of the foundation': of the old bridge at Teign- 

 mouth, five arches of which, after having been built only 12 years, fell 

 suddenly ; the construction of a new bridge llius became necessary, and it is 

 now in progress nnder the direction of Messrs. W^alker and Burges. The 

 worm is described as entering the wood through a hole not larger than 

 a pin, and perforating the timber in all directions, but chiefly in the direc- 

 tion of the fibre, at the same time increasing the size of the holes even 

 sometimes to an inch diameter ; a few of the worms had been found of the 

 extraordinary length of 3 ft. They confine their operations between low- 

 water mark and tlie bottom of the river, show ing that they cannot exist out 

 of water. 



A specimen of part of a log picked up off Jersey was as much perforated, 

 but ill a different manner, the worms having peuetr.ited the wood indiscrimi- 

 nately all over the surface ; in some cases leaving in the holes a coat 

 resembling the tail of a lobster about 3 in. in length, which showed that the 

 ravages had been committed by the " Lymnoria Terebrans." 



The paper was also accompanied by a specimen of wood sheathing charged 

 with nails, from the bottom of a vessel believed to be about 100 years old, 

 together with some of the worms (" Teredo Navalis"), for the purpose of 

 showing the peculiar shape of the head^ — resembling a pair of forceps, with 

 which they cut away the wood. 



" Description of the Roof of Messrs. Simpson and Co's Factory." By 

 John Boustead, Grad. Inst. C.E. 



The truss of this roof is double, consisting of two frames cf Memel 

 timber. The principals are fitted into cast iron shoes resting on the walls, 

 with projections let into the wall plates ; they taper towards the ridge, 

 and there abut against a cast iron ring-piece, througli which a wrought iron 

 bolt IJ in. diameter passes, and answers the purpose of a king-post in sup- 

 porting the collar-beam. To the under side of this beam is attached a heel 

 and eye-plate, to either end of which are linked bolts passing between the 

 principals, and secured by nuts at the backs of the shoes, thus forming effi- 

 cient ties to resist the thrust of the principal rafters. 



The slate-boards are supported by five purlins 4 ft. apart, and abut against 

 a ridge-piece resting on the kings. 



The span of the roof is 34 ft. 3 in. The pitch is about 3 to 1 , and the 

 principals are placed 9 ft. apart. 



The scantlings of the principal timbers are: — Principals 9J by 2J in. 

 tapering to C.V by 2 J- in. ; coUar-beam 7 by 3 J in. ; purlins 6 by 4 in. ; wall- 

 plates 6 by 4 in. ; slate-boards 1 in. tliick ; ridge-piece 10 by 2 in. 



The principals were sawn out by a template, so as to insure the given taper 

 and the accuracy of the angles of the ends ; they were then laid in a hori- 

 zontal position ])Iaced at the required angle, and the collar-beam inserted 

 .V in. deep into each principal, and secured by bolts | in. diameter; the mode 

 of raising the roof is then described. 



Some of the advantages of rjufs of this construction are stated to be, 

 economy in materials and workma^iship, with lightness and simplicity, and 

 that all sagging of the timbers uiLiy be rectified by screwing up the nuts of 

 the kings and shoes. 



The truss is recommended for buildings where lofty apartments or coved 

 ceilings are required, and also for its presenting so few points for the suspen- 

 sion of heavy weights that may subject the timbers to strains for which no 

 provision baa been made. 



From the examinations that have been made, this roof seems to answer 

 satisfactorily ; it has been erected three years and a half, and has sustained 

 heavy falls of snow, but the ridge and rafters have preserved their lines per- 

 fectly, and the walls show no signs ni" having been subjected to undue 

 pressure. The design of the roof is siru, le, its appearance light, and it may 

 be considered an interesting specimen of the art of simple carpenti^ assisted 

 by iron-work. 



A drawing of the truss accompanied tiie paper. 



ACADEMY OF SCIENCES. 



April 4. — M. Siguer read a paper On the means of preventing the explosion 



of boilers in .steam vessels, or of confining the effects of such explosions, when 

 they do occur, within very circumscribed limits. He recommends, as a 

 general principle, that the boilers should be composed of many distinct 

 parts (tubes), so that in the event of the rupture of any one portion, there 

 may be no injury beyond the engine-room, and that the metal of which they 

 are' composed should be thin, in order that it may not be deprived of its 

 tenacity in the process of manufacture; and he insists upon strict attention 

 being paid to their shape, which should, he says, be spherical, cylindrical, or 

 conical, as being best calculated to offer an equal resistance to the explosive 

 power. 



M. Arago communicated the result of some experiments made with the 

 view of solving the long-disputed question as to whether the iraiismission of 

 light is more or less rapid, according to the density of the medium through 

 which it passes, and reported his experiments before the Academy in proof 

 that the transmission is not equally rapid. 



