32 ANNUAL OF SCIENTIFIC DISCOVEEY. 



as tightly as possible over pulleys at every bearing of the tube. This 

 wire formed the datum from which all movements were to be meas- 

 ured on slips of card attached to vertical staves at various points along 

 the tube. 



During the two days occupied with the test the public were rigor- 

 ously excluded. At each slip of paper one of his assistants was 

 placed, and provided with a lamp and a pencil, by which to make the 

 necessary marks. The loaded train was then taken hold of by two 

 of the most powerful engines belonging to the Grand Trunk, and, with 

 extreme difficulty from the great weight, brought into the first two 

 tubes, bevond which all their united efforts failed to draw it. A third 



t/ 



engine having been obtained, the three were loarely able to force the 

 load along to the centre of the bridge ; when night coming on, the 

 test of the remaining portion of the bridge was deferred until the fol- 

 lowing day. 



Early next morning, the interesting experiment was resumed, and 

 concluded during the day. 



In giving the result of the fearful ordeal to which the tubes were 

 subjected, we will only note the deflection on a pair of the side tubes 

 the others being similar, and the central one. 



When the train covered the first tube, the deflection in the centre 

 amounted to seven- eighths of an inch, and the adjoining one, to which 

 it was coupled, was lifted in the middle three-eighths of an inch. The 

 load then being placed over both tubes, the deflection was the same in 

 each, or three-fourths of an inch in, the middle ; and on being entirely 

 removed, both tubes resumed their original level. The large centre 

 span, entirely disconnected from the other tubes, on being covered 

 with the loadthroughout its entire length, deflected in the centre 

 only one inch and seven-eighths, and came back to its previous level 

 on the load being removed. 



All these results were considered highly satisfactory, as being con- 

 siderably within the calculated deflection for such a load according 

 to formulae well known and generally made use of. 



jSTothing exemplified more strongly the confidence felt by 'Mr. 

 Hodges in the strength of the work than the severe test to which he 

 exposed it. The writer well remembers the " peculiar feelings " he 

 experienced when standing at the marking-post assigned him, sur- 

 rounded at the same time by an Egyptian darkness, dense enough to 

 be felt, arising from the condensed steam and the smoke of the engines, 

 and totally obscuring the light of a glass lamp two feet distant. To 

 thus stand closely pressed up against the side of the tube, with eyes 

 and lamp brought within a few inches of the datum-line, intently 

 watching its movements, and leaving but sufficient room for the slip- 

 ping, groaning, puffing, but invisible engines and their heavily-loaded 

 cars to pass, with but a quarter of an inch of boiler-plate between 

 time and eternity ; or, when mentally reasoned back to safety and 

 security, and while listening, during the stoppage of the train, to the 

 surging, cracking, crashing ice far below, as it swept past, to have 

 those feelings of personal security dissipated in a moment by the 

 thought of an over-loaded car breaking down and burying the deflec- 

 tion-observer beneath its weight, was surely reason enough for the 

 existence of the " peculiar feelings " alluded to. 



