EXPERIMENTS UPON WROUGHT-IRON GIRDERS. 28D 



Table V. 



Summary of Results. 



From the above it would appear that, within the limits of one-fourth the 

 breaking weight, wrought-iron beams are perfectly safe, as may be seen from 

 the results of Tables I. and II., where 1,000,000 changes were effected with- 

 out any visible deterioration of the material ; and if we add to this the results 

 of Table IV., we have upwards of 4',000,000 changes, which, at 30 trains per 

 diem over the Spey Bridge, would be equivalent to the prolonged period of 

 400 years. Now as we do not advise bridges to be loaded beyond one-sixth 

 of the load that would break them, Ave may reasonably consider tliem per- 

 fectly secure for a mucii longer period of time. Much, however, depends 

 on the quality of the material, and a sound principle of uniting the joints, ail 

 of which have been determined by experiment when devising the plans and 

 designs for the Britannia and Conway Tubular Bridges. To these we may 

 safely refer, and above all to the selection of the material, which in those 

 parts of girders subjected to a tensile strain should be of the best double 

 wrought plates, and equal to a test of 22 to 24 tons per square inch. The 

 use of this superior quality of iron for the bottom flanges of girders would 

 give an increase of one-tenth of strength to that of common boiler plates. 



There is no economy in the use of inferior material for this purpose; as 

 its employment is attended not only with loss of character, but is highly dan- 

 gerous as regards the public safety. 



The Law of Patents. 



Mr. James Heywood, M.A., F.R.S., read the Report of the Committee on 

 the Patent Laws, which was founded upon, and embodied the following re- 

 solutions, agreed upon by the Patent Committee in London : — 



1. That all applications for grants of letters patent should be subjected to 

 a preliminary investigation before a special tribunal. 



1861. V 



