142 SECTIONAL ADDRESSES. 



the flow of fluids had been carried out, relative velocities, momentum 

 and kinetic energy were well understood and the next step was made by 

 Poncelet in 1832, who enunciated the guiding principles underlying the 

 design of vanes receiving moving fluids, and from that time progress has 

 been so remarkable that to-day water turbines of more than 70,000 h.p. 

 having efficiencies greater than 80 per cent, are being constructed and 

 millions of horse power are being generated by water-power. The brilliant 

 achievements in the development of the steam turbine of Sir Charles 

 Parsons and others following in his steps are to-day well known. At the 

 beginning of the nineteenth century there were probably 10,000 engines 

 in England giving a total horse-power of about 200,000. To-day steam 

 turbines each capable of developing more than 200,000 h.p. have been 

 or are being made for stations in various parts of the world. It seems 

 very doubtful if this could have been possible except as a consequence 

 of the work of Poncelet and two centuries of scientific experiment. It 

 is fifty years ago this year since the first food-carrying ship was fitted 

 with refrigerating plant ; if experiment and thermodynamic theory had 

 not shown the way a commencement would hardly have been conceivable, 

 and the developments of refrigeration, which are of such importance in 

 the food supplies of to-day, would hardly have been possible. To many 

 other examples of the direct indebtedness of engineering to science 

 reference might be made. The rapid developments of high-tension 

 distribution of power have been made possible by research in the labora- 

 tory. Many attempts had been made to utilise the explosive force of 

 gunpowder, hydrogen, and coal gas for power production before the 

 modern four-cycle internal combustion engine was developed, but with- 

 out success, until it was recognised from thermodynamical considerations 

 that compression is essential before ignition. The principles of geo- 

 metrical and dynamical similarity based upon strict mathematical 

 reasoning have been of the greatest service in the development of ships, 

 aeroplanes, and airships. In 1862 a committee of the British Association 

 reported that models could not be used to determine the resistance of 

 ships. William Froude, however, disagreed with the committee and 

 enunciated his well-known principles of similarity and showed how the 

 wave-making and frictional resistances could be separated from each 

 other and the total resistance of the ship obtained from experiments on 

 models. Osborne Reynolds and Raleigh extended the argument to 

 fluids having different densities and coefficients of viscosity, and it is tlfus 

 possible from experiments in one medium to anticipate the resistance 

 and forces acting upon similar models in other fluids. By using Clerk 

 Maxwell's elegant principles of reciprocal displacements the forces and 

 moments acting in statically indeterminate structures can be determined 

 experimentally from models, which cannot be obtained, or only with 

 great difficulty, by mathematical analysis. Sir David Brewster, one of 

 the founders of the British Association, discovered more than a century 

 ago that transparent substances when subjected to stress require double 

 refractiVe properties. Taking advantage of this property, Professor 

 Coker, uWng the precise aids of optics and mathematics, has from models 

 been abile to throw much light upon the nature and magnitude of the 

 stresses iln structures and machine elements. The work of Sorby on the 



