CHAP. XIX. 



THE TUBE FALLS. 



437 



be left to chance or good luck.' And fortunate it was 

 that I insisted upon this cautious course being pursued ; 

 for, one day, while the hydraulic presses were at work, 

 the bottom of one of them burst clean away ! The 

 crosshead and the chains, weighing more than 50 tons, 

 descended with a fearful crash upon the press, and the 

 tube itself fell down upon the packing beneath. Though 

 the fall of the tube was not more than nine inches, it 

 crunched solid castings, weighing tons, as if they had 

 been nuts. The tube itself was slightly strained and 

 deflected, though it still remained sufficiently serviceable. 

 But it was a tremendous test to which it was put, for a 

 weight of upwards of 5000 tons falling even a few 

 inches must be admitted to be a very serious matter. 

 That it stood so well was extraordinary. Clark imme- 

 diately wrote me an account of the circumstance, in 

 which he said, ' Thank God, you have been so obstinate. 

 For if this accident had occurred without a bed for the 

 end of the tube to fall on, the whole would now have 

 been lying across the bottom of the Straits.' Five 

 thousand pounds extra expense was caused by this 

 accident, slight though it might seem. But careful 

 provision was made against future failure ; a new and 

 improved cylinder was provided ; and the work was 

 very soon advancing satisfactorily towards completion." 1 



1 The hydraulic-presses were of an 

 extraordinary character. The cylin- 

 ders of those first constructed were of 

 wrought-iron (cast-iron being found 

 altogether useless), not less than 8 

 inches thick. They were tested by 

 being subjected to an internal pressure 

 of 3 or 3 tons to the circular inch. 

 The pressure was such that it squeezed 

 the fibres of the iron together ; so that 

 alter a few tests of this kind the 

 piston, which at first fitted it quite 

 closely, was found considerably too 

 small. "A new piston," says Mr. 

 Clark, " was then made to suit the en- 

 larged cylinder ; and a further enlarge- 

 ment occurring again and again with 



subsequent use, the new pistons be- 

 came as formidable an obstacle as the 

 cylinders. The wrought-iron cylin- 

 der was on the point of being aban- 

 doned, when Mr. Amos (the iron 

 manufacturer), having carefully gauged 

 the cylinder inside and out, found to 

 his surprise, that although the inter- 

 nal diameter had increased consider- 

 ably, the external diameter had re- 

 tained precisely its original dimen- 

 sions. He consequently persevered in 

 the construction of new pistons; and 

 ultimately found that the cylinder 

 enlarged no longer, and to this day 

 it continues in constant use. Layer 

 after layer having attained additional 



