64 The Motion of a Perfect Liquid. [Feb. 10, 



those of actual ships', or of liquid moving through ordinary channels 

 of varying section, even for the case of a perfect liquid, but he has 

 had to take those cases, and tbey are very few indeed, that he has 

 been able to discover which fit in with his mathematical powez'S of 

 treatment. 



This brief summary may possibly serve to indicate the nature of 

 the difficulties which 1 have pointed out, and will show you the vast 

 field there yet lies open for research in connection with the subject of 

 hydromechanics, and the great reception which awaits the discovery 

 of a theoretical method of completely dealing with viscous liquids, 

 instead of having recourse as at present principally to empirical 

 formula based on ihe simple law already alluded to. 



We may, however, console ourselves with the thought, that in the 

 application of the laws of motion theinselvi s to any terrestrial matters, 

 the friction of budies must always be taken into account, and renders it 

 necessary, that we should commence by studying the ideal conditions. 

 In this as in other matters the naval architect and engineer must always 

 endeavour as far as possible to base their considerations and work upon 

 the secure foundation of scientific knowledge, making allowances for 

 disturbing causes, which then cease to be the source of perplexity and 

 confusion. From this point of view, the study of the behaviour of a 

 perfect liquid, even when no such form of matter appears to exist, has 

 an interest for the practical man in spite of the deviation of actual 

 liquids from such ideal conditions. If the truth must be told, it is 

 such a deviation from the simple and ideal conditions that really con- 

 stitute the work of a professional man, and it is only practical expe- 

 rience which, based tipon sound technical knowledge, enables 50,000 

 tons of steel to be made to span the Firth of Forth, Niagara to be 

 harnessed to do the work of 100,C00 horses, or an ' Oceanic ' to be slid 

 into the sea with as little misgiving as the launch of a fishing boat. 



1 have, I am afraid, brought you only to the threshold of a vast 

 subject, and in doing so, have possibly employed reasoning of too 

 elementary a kind. After all, I may plead that I have followed the 

 dictum of Faraday, who said, " If assumptions must be made, it is 

 better to assume as little as possible." If I have assumed too little 

 knowledge on your part, it is because of the difficulties I have found 

 in the subject myself. If I have left more obscure than I have been 

 able to make clear, it is consoling to think how many centuries were 

 required to discover even what is known at the present time, and we 

 may well be forgiven if we cannot grasp at once results which repre- 

 sent the life-work of some of the greatest men. 



