1916] 



WEEKLY EVENING MEETING, 



Friday, February IS, 1016. 



Colonel E. H. Hills, C.M.G. RE. D.Sc. F.Ft.S., Secretary 

 and Vice-President, in the Chair. 



Professor Ernest G. Coker, M.A. D.Sc. M.Inst.C.E. M.Pt.I. 

 Polarized Light and its Applications to Engineering. 



One of the fundamental questions which arises in the majority of 

 engineering problems is the design of a structure or machine which 

 will carry out some pre-determined work in an efficient and 

 economical manner, and whatever the problem may be, it is almost 

 invariably bound up with the arrangement of a number of connected 

 parts designed to resist loads which are imposed upon them. 



The machines and structures which the engineer has to construct 

 are almost infinite in their variety, and each one usually presents a 

 new and a difficult problem, especially as regards the stresses which 

 m ly be imposed upon its parts, and the way in which these stresses 

 are distributed. 



The application of science to the determination of the internal 

 stresses in materials loaded in any given manner, offers, in fact, a 

 great field of inquiry which has resulted on the one hand in a highly 

 developed mathematical theory of the strength of materials, and on 

 the other, in a vast number of experimental investigations upon the 

 physical properties of engineering materials ; and it is upon the data 

 which mathematical and physical researches provide, that the engi- 

 neer must depend for guidance in designing safe and economical 

 structures and machines. 



It is, I think, a common experience among engineers to find 

 themselves confronted with a stress problem in their designs which, 

 even with all their accumulated wealth of knowledge, presents almost 

 insoluble difficulties ; it often defies mathematical processes, and is 

 beyond the scope of any previous physical investigation. But it 

 must be solved, if only approximately, and the imperative need of 

 an answer, renders it advisable to make experimental investigations 

 before proceeding with an important work of construction. 



It is perhaps somewhat severe, but not untrue, to say that 

 engineers have not always made the fullest use of the discoveries of 

 pure science in their practice ; and it is remarkable that a discovery 

 of Sir David Brewster, in 1816, that transparent materials when 



