118 THE MOTION OF A PERFECT LIQUID. 



it necessaiy that we should commence b}" studying the ideal conditions. 

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

 pJways endeavor, as far as possible, to base their considerations and 

 work upon the secure foundation of scientific knowledge, making allow- 

 ances for disturbing causes, which then cease to be the source of per- 

 plexity and confusion. From this point of view the study of the 

 behavior 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 'u\on\ conditions. If the truth must be told, 

 it is such a deviation from the simple and ideal conditions that really 

 constitutes the work of a professional man, and it is onl}^ practical 

 experience which, based upon 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 100,000 horses, or an Oceanic to be slid 

 Mito 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 sub- 

 ject, and in doing so have possibly employed reasoning of too ele- 

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

 of Faraday, who said, "If assumptions must l)e 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 difiiculties I have found in the subject 

 myself. If I have loft 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 can not grasp at once results which represent the life 

 work of some of the greatest men. 



