428 



ROBERT STEPHENSON'S CAUTION. 



CHAP. XIX. 



was strongly inclined to retain them. 1 Mr. Fairbairn 

 held that it was quite practicable to make the tubes 

 " sufficiently strong to sustain not only their own weight, 

 but, in addition to that load, 2000 tons equally distri- 

 buted over the surface of the platform, a load ten times 

 greater than they will ever be called upon to support." 



It was thoroughly characteristic of Mr. Stephenson, 

 and of the caution with which he proceeded in every 

 step of this great undertaking probing every inch of 

 the ground before he set down his foot upon it that he 

 should, early in 1846, have appointed his able assistant, 

 Mr. Edwin Clark, to scrutinise carefully the results of 

 every experiment, whether made by Mr. Fairbairn or 

 Mr. Hodgkinson, and subject them to a separate and 

 independent analysis before finally deciding upon the 

 form or dimensions of the structure, or upon any mode 

 of procedure connected with it. That great progress 

 had been made by the two chief experimenters before 

 the end of 1846, appears from the papers read by Messrs. 

 Fairbairn and Hodgkinson before the British Association 

 at Southampton in September of that year. In the 

 course of the following month Mr. Stephenson had be- 

 come fully satisfied that the use of auxiliary chains was 



1 The following passage occurs in 

 Robert Stephenson's Report to the di- 

 rectors of the Chester and Holyhead 

 Railway, dated the 9th February, 

 1846 : " You will observe in Mr. 

 Fairbairn's remarks, that he contem- 

 plates the feasibility of stripping the 

 tube entirely of all the chains that 

 may be required in the erection of the 

 bridge; whereas, on the other hand, 

 Mr. Hodgkinson thinks the chains 

 will be an essential, or at all events a 

 useful auxiliary, to give the tube the 

 requisite strength and rigidity. This, 

 however, will be determined by the 

 proposed additional experiments, and 

 does not interfere with the construction 

 of the masonry, which is designed so 

 as to admit of the tube, with or with- 



out chains. The application of chains 

 as an auxiliary has occupied much of 

 my attention, and I am satisfied that 

 the ordinary mode of applying them 

 to suspension bridges is wholly inad- 

 missible in the present instance; if, 

 therefore, it be hereafter found neces- 

 sary or desirable to employ them in 

 conjunction with the tube, another 

 mode of employing them must be de- 

 vised, as it is absolutely essential to 

 attach them in such a manner as to 

 preclude the possibility of the smallest 

 oscillation. In the accomplishment 

 of this I see no difficulty whatever ; 

 and the designs have been arranged 

 accordingly, in order to avoid any 

 further delay." 



