830 TKAN8ACTI0NS OF SECTION G. 



WEDNESDAY, SEPTEMBER 9 



The following Papers were read : — 



1. Experiments on Rotating Discs} 

 By John Brown, F.R.S., and Maurice F. FitzGerald, B.A. 



The authors began by referring to the difficulty of the mathematical analysis 

 of the elastic deformation, under centrifugal stress, of rapidly revolving discs, 

 particularly when formed with a central hole, surrounded by a thick boss, 

 gradually reduced outwards to a thin edge by an arbitrary curve, and mentioned 

 the investigations of Mr. Chree aud Mr. F. Purser of the cases of cylinders and 

 ellipsoids. The authors' experiments were described as made for the purpose of 

 finding out whether approximate formulfe, such as have been given for cases in 

 practice in such worlis as that of Stodola on steam-turbines, are sufficiently nearly 

 correct for practical purposes. Two discs, made of red rubber, weighing 72 lb. 

 per cubic foot, were tested. The discs were both 12 inches external diameter. 

 One was solid, k inch thick at edge, 2 inches at the centre, its surfaces being two 

 Hat cones. The other was g inch thick at edge, in its centre was a hole 1^ inch 

 diameter, surrounded by a boss, with flat ends, 2h inches diameter and 3 inches 

 thick, the surfaces between the edges of the boss and disc being shaped to hollow 

 hyperbolic curves. The discs were suspended from the end of the shaft of a small 

 motor, placed with its axis vertical, and circles drawn on the faces, previously 

 painted white, while spinning. Photographs being taken of the discs while 

 spinning and when at rest, the strains at different radii were found by comparison 

 of the photographs, and plotted .as curves, shown by lantern slides. The results 

 were compared with those of approximate formulae. In the case of the solid disc 

 the difference between the speeds causing a given strain, as calculated and as 

 observed, amounts to about 20 per cent., and may, considering the imperfect 

 elasticity of indiarubber, be considered a fair enough approximation; but in the 

 case of the other disc, though the formula gives a tolerably fair idea of the shape 

 of the curve of strains, its error as to the actual magnitude of the speed causing 

 a given strain is so great, being near 400 per cent., as to lead to the conclusion 

 that the formula could not be trusted for practical purposes. 



2. General Urban and Inter-urban Transportation and Railless Electric 

 Traction."^ By F. Douglas Fox, M.Inst.C.E. 



3. The Strength of Solid Cylindrical Round-ended Columns.^ 

 By Professor W. E. Lilly, M.A., D.Sc. 



In some previous papers * by the author the importance of secondary flexure 

 and its influence on the strength of columns was demonstrated. The result of 

 these researches led to a revision of the formulfe at present in use for the design 

 of columns. It was shown that some provision requires to be made for the wave 

 deformation due to secondary flexure, which depends upon the thickness and the 

 figure or shape of the cross-section of the column. A modified formula based 



' Keported fully, with illustrations, in EiigineeHng, September 18. 



2 Published in Engineering, September 18. 



3 Published in Page's Magazine, September 18. 



* References to previous papers : ' The Strength of Columns,' Proceedings of 

 the Institution of Mechanical Engineers, June 1905; 'The Economic Design of 

 Columns,' Proceedings of the Institution of Civil Engineers of Ireland, March 

 1907 ; ' The Design of Struts,' Engineering, January 10, 1908. 



