420 POPULAR LECTURES AND ADDRESSES. 



highly important suggestion of Sir Richard 

 Collinson, to use a high and a low note in 

 direct contrast, to give characteristic sounds for 

 lighthouses, may be worked out systematically in a 

 very convenient manner by using the combinations 

 of the preceding table ; with a high note instead of 

 the short eclipse, and a low note instead of the long 

 eclipse ; the low note of the same duration as the 

 high note ; the interval between the notes of each 

 group about the same as the time of each blast ; 

 and the interval of silence between the group of 

 blasts much longer than the whole time of each 

 group. When the fog-siren is used there is no 

 difficulty in making the blasts as short as we please, 

 and they certainly ought not to be longer than a 

 half-second or three-quarters of a second. Quick- 

 ness is here, as in many other nautical matters, of 

 vital importance. Let any one try for himself, 

 sounding a high and a low note in rapid succession, 

 or two high notes and a low, or any other of the 

 combinations of the preceding table, and he cannot 

 fail to be convinced there is in each case a charac- 

 teristic sound, which needs no musical ear for its 



