2 ANNUAL OF SCIENTIFIC DISCOVERY. 



all four of the tubes, the deflections being carefully noted. These 

 deflections, in every case, by means of a nice apparatus for the pur- 

 pose, were ascertained to be exactly three fourths of an inch over 

 the immense mass and area of iron. After an interesting rehearsal 

 of these experimental ordeals, which occupied several hours, the train 

 of 280 tons, with its two locomotives, was taken out about a mile dis- 

 tant from the tube, and then suddenly shot through it with the greatest 

 attainable rapidity, and the result was very interesting, as determining 

 a much-discussed question ; it being found that the deflection at this 

 immense velocity of the load was sensibly less, in the way of undula- 

 tion or collapse, than when the load was allowed to remain at rest in 

 the tube. The manner in which these results were registered and 

 arrived at was by means of a new and curious contrivance, it being 

 found that the tremor occasioned by trains in transit prevented these 

 deflections from being accurately read by the ordinary spirit-level. 

 This contrivance consists in a large pipe containing water, laid along 

 the lower cells of the tube, one end rising up within the tube at, the 

 centre, and the other end fixed against the stonework of the abut- 

 ments of the bridge. Both extremities of this pipe are furnished with 

 glass tubes and graduated scales, by which the relative levels of the 

 water are easily ascertained. As the slightest leakage or evaporation 

 over the ordinary thermometric expansion of the water would derange 

 the level, while only half the actual deflection of the tube was regis- 

 tered at each end of the pipe, these disadvantages are obviated by the 

 addition of a large reservoir of water in the interior of the tube, which 

 is covered with oil and placed beside the graduated scale. This larger 

 area exhibits the whole of the deflections at the abutment extremity, 

 and the apparatus presents a perfect mirror of all the deflections of 

 the great structure. 



" We learn from Messrs. E. and L. Clark, the resident engineers, 

 who have watched minutely, from day to day, all the developed pe- 

 culiarities of the novel undertaking, many curious and interesting 

 results. These gentlemen state that the heaviest gales through the 

 Straits do not produce so much motion over the extent of either tube 

 as the pressure against the side of the tube of ten men ; and that the 

 pressure of ten men, keeping time with the vibrations, produces an 

 oscillation of 1 inch, the tube itself making 67 double vibrations per 

 minute. The strongest gusts of wind that have swept up the channel 

 during the late stormy weather did not cause a vibration of more than a 

 quarter of an inch. The broadside of a storm causes an oscillation of less 

 than an inch ; but when the two tubes are braced together by frames, 

 which is now being done, these motions will be almost annihilated, 

 and all apprehension from wind or weather, from their being secured 

 together, will cease. The meteorological results since the tubes have 

 occupied their elevation have materially differed from those that were 

 observed when they lay along the Caernarvonshire coast. The action 

 of the sun at midday, instead of bending them two or three inches, 

 does not move them more than two or three eighths of an inch. The 

 daily expansion and contraction of the tubes varies from half an inch 

 to three inches, attaining either the maximum or minimum at about 



