TRANSACTIONS OF SECTION G. 789 



from active practice, devoted his abilities to experiments on the motion and resist- 

 ance of ships in water, which have proved of inestimable value to the naval 

 architect, and which formed the subject of his presidential address to this Section 

 in 1875. 



Electrical engineering' is specially adapted for experimental investigation ; and, 

 in this branch, theory and practice are so closely allied that some of the irost eminent 

 exponents of the theory of the subject, such as Lord Kelvin and Dr. Ilopkinson, 

 have developed their theories into practical results. In most other branches, the 

 investigator is generally distinct from the engineer in large practice ; but it may 

 be safely said that an able iniestigator and geueraliser in engineering science, as, 

 for instance, the late Professor liankine, accomplishes work of more value to the 

 profession at large than the practical engineer, who, in the world's estimation, 

 appears the more successful man. 



Every branch of engineering science is more or less capable of being advanced by 

 experimental investigations •, and when it is borne in mind that the force of waves, 

 the ebb and flow of tides in rivers, the influences of training works in estuaries^ 

 and the motion of ships at sea have been subjected to experimental research, it ap- 

 pears impossible to assign a limit to the range of experiments as a means of extending 

 engineering knowledge. Problems of considerable interest, which can only be 

 solved by experiments or by comprehensive generalisations from a number of 

 examples, must frequently present themselves to engineers in the course of their 

 practice, as they have to myself; and engineers would render a great service to 

 the profession if they would follow up the lines of investigation thus suggested to 

 them, in the true spirit of scientific inquiry. 



Failures of Works due to Neglect of Scientific Considerations.— Before the 

 amount and distribution of the stresses in structures were thoroughly understood, 

 a disposition was naturally evinced to err on the side of excessive strength ; and 

 the materials in the various parts of the structure were not suitably proportioned 

 to the load to be borne, resulting in a waste of materials and too great an expen- 

 diture ou the works. Thus some of the early high masonry reservoir dams in 

 Spain exhibit an excessive thickness towards the top, imposing an unnecessary load 

 on the foundations ; and in many of the earlier iron girder bridges more material 

 was employed than was required for stability, and it was not properly distributed. 

 Boldness engendered by increased experience, and dictated by motives of economy, 

 has tended to make the engineers of the present day pursue an opposite course ; 

 and, under these circumstances, the correct calculation of the strains, the exact 

 strength of the materials, and a strict appreciation of the physical laws affecting the 

 ■designs become of the utmost importance. 



The failures of many bridges may be explained by errors in design, defects in 

 ■construction, or by economy carried beyond the limits" of safety in pushing forward 

 railways in undeveloped countries ; but other failures are attributable "to a dis- 

 regard or undejestimation of the influence of physical causes. Thus the Tay Bridge 

 disaster, m 1S79, was due to underestimating the amount and effect of the wind- 

 pressure in an exposed situation, where it acted with a considerable leverage, owing 

 to the height of the bridge, and was inadequatelyprovidedagainst by the small trans- 

 Terse width of the piers in proportion to their height, which were further weakened 

 by bad workmanship in the bracing of their columns. The bursting of the Bouzy 

 masonry dam in France this year must be attributed to an inadequate thickness 

 at part of the cross-section, producing a tensional strain on the inner face with the 

 reservoir full, aided by the instability resulting from a fissured foundation. The 

 overthrow of the outer arms of the Madras breakwaters, during a cyclone in 1881, 

 may be traced to an inadequate estimate of the force of the waves in a storm, in deep 

 water, and with a great fetch across the Indian Ocean, beating against the portions 

 of the breakwaters directly facing their course ; for these outer portions, running 

 nearly parallel to the coast-hne, were net made any stronger than the inner portions 



p. 142 ; and Amelioration de la Partie Maritime des Fleures, y compris leurs Em- 

 boucJivres, L. F. Vernon-Harcourt, Paris Inland Navigation Congress, 1892, pp. 27-29 

 an^d 32, 33, and plate 3. = <= > rr 



