64 YEAR-BOOK OF FACTS. 



by it, in order to prevent its coming into contact with the atmo- 

 sphere ; when the mixture is to be gradually heated, and at length 

 exposed to a heat capable of melting iron. Where the fire is well 

 kept up, an hour will generally be found a sufficient time to convert 

 two pounds of iron into excellent and exceedingly hard steel, capable 

 of being forged. — Correspondent of the Mechanics Magazine. 



SUSPENSION CHAINS AND GIRDERS. 



Mr. P. W. Barlow has read to the British Association a paper 

 " On the Mechanical Effects of combining Suspension Chains and 

 Girders, and the Value of the Practical Application of the System," 

 illustrated by a large model. The object of the paper is to. point 

 out that such bridges are adapted for carrying railway traffic, and 

 are less costly than the bridges usually adopted in this country for 

 that purpose. 



In the discussion on Mr. Barlow's paper, the chairman, Mr. 

 Pairbairn, Mr. Froude, and Mr. E. Cowper, took part ; the latter 

 gentleman pointing out that, in his opinion, danger would result 

 from the rapid wear and tear of the rivets joining the links of the 

 chain ; and he suggested and described a bridge, on the suspension 

 principle, formed of boiler-plate of such a curve above, and such a 

 horizontal line below for supporting the platform, and of such depth 

 as to include in it all the curves of distortion which the catenary 

 would undergo when subjected to the varying load of trains passing 

 over a bridge suspended from it. This combines the necessary 

 rigidity with the suspension principle. 



STRENGTH OF WROUGHT-IRON GIRDERS. 



Mr. Fairbairn has communicated to the British Association 

 certain " Experiments to determine the Effects of Vibratory Action 

 and Long-continued Changes of Load upon Wrought-iron Girders." 

 The paper is entirely of a technical character, and details the re- 

 sults of a set of experiments having for their object the determining 

 matters with which the public are intimately concerned, viz., the 

 efficacy of girders supporting bridges over which railway trains 

 are constantly passing. It is well known that iron, whether in the 

 shapes of railway axles or girders, after undergoing for a length of 

 time a continued vibratory or hammering action, assumes a different 

 molecular structure, and though perfectly efficient in the first instance, 

 becomes brittle and no longer capable of sustaining the loads to 

 which it may be subjected. Mr. Fairbairn slated that tin practical 

 conclusion to which his experiments, so far as they had at present 

 gone, would lead was, that a railway girder bridge would, irrespective 

 of other causes, last a hundred and fifty years. 



NEW ZEALAND Kl'l II. 



Ever since the settlement of New Zealand by Europeans their 

 attention haB been daily called to the peculiarities of a Kind of metallic 



sand along the shores of Now Plymouth, in Tarauaki. This Band 

 has the appearance of fiuo steel filings, and if a magnet be dropped 



