122 POPULAR LECTURES AND ADDRESSES. 



involves risk of collision, which can only be 

 obviated by fulfilment of the first clause of 

 Art. 1 6. "Every steam ship, when approaching 

 another ship so as to involve risk of collision, 

 shall slacken her speed, or, if necessary, stop and 

 reverse." It is not too much to say that no 

 collision between two steamers, or between a 

 steamer and a sailing ship, ever occurred in 

 daylight, and in clear and moderate weather, 

 which could not have been avoided by the timely 

 observance of this rule by at least one of the two 

 vessels. 



64. Art. 10 of the Regulations which I have read 

 to you leads me to speak of the fog-horn, of which, 

 through the kindness of Mr. N. Holmes, I am able 

 to show you some very excellent specimens this 

 evening. You hear how loud even the smallest 

 of them is. 



The question how far a sound can be heard at 

 sea is a very difficult one, and involves some 

 exceedingly subtle principles regarding the pro- 

 perties of matter and problems of abstract 

 dynamics. In a paper by Professor Henry in 



