TRANSACTIONS OF THE SECTIONS. 265 



On Iron Construction ; with Bemarks on the Strength of Iron Columns and 

 Arches. By F. W. Sheilds, M.I.O.E. 



The author remarked, that in various constructions, such as bridges, ships, and 

 roofs, the materials formerly xised were being rapidly superseded by iron. Nor was 

 this change coniined to England and the seats of iron manufacture alone. In fact, 

 it appeared almost anomalous that a bridge of this costly material, conveyed from 

 England at great expense, should supersede with economy, in Australia, India, 

 Russia, or Spain, the apparently cheaper materials found in abundance on the spot. 



The explanation of this apparent anomaly is found in the gi-eater strength of 

 iron, size for size, than of the other materials, and in its capacity for being manu- 

 factured in such varied shapes and sizes, that just so much scantling may be 

 given to each part of a structure as will meet the strain on that part, without any 

 being wasted or lost to use. In a framing, an undue increase of scantling to some 

 of its parts does not add strength to the whole structure, as its endurance is 

 limited by the strength of its weakest part ; and such increase but involves the 

 addition of useless weight and expense, besides endangering the stability of the 

 construction by the failure of its weaker portions. 



It is therefore requisite, on the gi-ounds not only of economy but of safety, that 

 practical men dealing with ironwork should be versed in calculating the strains 

 upon such framings. The author would not attempt here to give an abstract of 

 these principles, as he had briefly stated them in a recent publication on the strains 

 on structures of ironwork ; but in the more simple cases of the resistance to 

 pressure of columns and arches, he would state the results of his experience. 

 After allusion to the experiments of Messrs. Fairbaim and Eaton Hodgkmson, he 

 stated that, from large experience in the construction of the Crystal Palace at 

 Sydenham and other works, he had adopted the following rules for the safe load 

 borne by cast-iron columns of good construction, with flat ends and with base-plates 

 at their bearings. For hollow colunms of 20 to 24 diameters in length, — 



Columns may be loaded with 

 If cast f inch thick or upwards. ... 2 tons per square inch sectional 



area of iron in column. 



the cause of the diminution in loading being that thin and light columns are 

 more liable to weakness from inequalities of casting. 



In the apportionment of iron to meet the strain or thrust of an arch, it is usual 

 to allow about 2^ tons of pressiure to each sectional inch in cast, and 4 tons in 

 wrought iron ; also, in very flat arches, to consider the flat central portion as a 

 girder, and to give to its top and bottom such flanges as a simple beam of its length 

 and depth would require. 



On Patent Tribunals. By W. Spence. 

 The author argued against the practicability of any plan of preliminaiy investi- 

 gation of the merits of inventions before granting patents in any form that had been 

 suggested. He, however, thought that the difliculties in the way of preliminary 

 investigation did not apply to the trial of cases after the flling of th'e complete 

 specifications, and he fully concun-ed in the necessity of a special tribimal for 

 trying patent cases. 



On the Defection of Iron Girders. By B. B. Stoney, M.R.I.A. 

 The author showed, by diagrams drawn to an exaggerated scale, that the deflec- 



