20 ANNUAL OF SCIENTIFIC DISCOVERY. 



them a flexible tube, air-tight. This tube has a series of slide-valves, 

 entirely under the care of a guard, who, by levers, has perfect control 

 over his train. Along the whole line of railway is laid a pipe, in 

 connection with which a series of pistons are fixed between the rails, 

 intended to receive the tube above mentioned in its passage. In these 

 pistons are atmospheric valves, opening into the fixed pipe, which is 

 always kept exhausted, so that when the train passes over the pistons, 

 the slide-valves in the tube are opened by means of inclined planes 

 communicating with the levers, which levers are raised up on the 

 train passing, the atmosphere existing in the tube to supply the 

 vacuum, and the train is impelled by external atmospheric pressure. 

 London Mining Journal, Sept. 7. 



APPLICATION OF IKON TO RAILWAY STRUCTURES. 



THE Civil Engineer and Architect' 's Journal for February contains 

 an important report from the commissioners appointed to inquire into 

 the application of iron to railway structures. They say, " As it soon 

 appeared, in the course of our inquiry, that the effects of heavy 

 bodies, moving with great velocity, upon structures, had never been 

 made the subject of direct scientific investigation, our attention was 

 early directed to the devising of some experiments for the purpose of 

 elucidating this matter. The questions to be examined may be ar- 

 ranged under two heads, viz. : 



" 1. Whether the substance of metal which has been exposed for a 

 long period to percussions and vibrations undergoes any change in the 

 arrangement of its particles, by which it becomes weakened ? 2. 

 What are the mechanical effects of percussions, and of the passage 

 of heavy bodies, in deflecting and fracturing the bars and beams upon 

 which they are made to act ? 



" A great difference of opinion exists among practical men with 

 respect to the first of these questions. Many curious facts have been 

 elicited by us in evidence, which show that pieces of wrought-iron 

 which have been exposed to vibrations, such as the axles of railway 

 carriages, the chains of cranes, &c., employed in raising heavy 

 weights, frequently break after long use, and exhibit a peculiar crys- 

 talline fracture and loss of tenacity, which is considered by some en- 

 gineers to be the result of a gradual change produced in the internal 

 structure of the metal by the vibrations. Others contend that this 

 peculiar structure is the result of an original fault in the process of 

 manufacture, and deny this effect of vibration altogether, whilst some 

 allege that the crystalline structure can be imparted to fibrous iron in 

 various ways, as by repeatedly heating a bar red-hot, and plunging it 

 into cold water, or by continually hammering it, when cold, for half 

 an .hour or more. Mr. Brunei, however, thinks the various appear- 

 ances of the fracture depend much upon the mode in which the iron is 

 broken. The same piece of iron may be made to exhibit a fibrous 

 fracture when broken by a slow, heavy blow, and a crystalline fracture 

 when broken by a sharp, short blow. Temperature alone has also a 

 decided effect upon the fracture ; iron broken in a cold state shows a 



