6 Prof. J. Joly on Scientific 



which he sees the first light-flash. If the sound comes to 

 him along with the 2nd flash he must be 2 cables distant,, 

 and if with the 10th flash he is 10 cables from the 

 buoy. Thus he has only to count up the flashes till he hear& 

 the bell, and the result is the number of cables which 

 separate him from the buoy. 



The value of this buoy to small craft is more especially 

 evident when we remember that such craft are to a great 

 extent debarred from the use of wireless and submarine 

 signals. Expert knowledge denied to the humble skipper is 

 required for the care and use of the former; and the small 

 draught reduces seriously the efficiency of the latter. 



We can picture now the working of this simple and 

 inexpensive substitute for the lightship on dark and wild 

 nights. When the sailor picks up the light he is, maybe, 

 some three or four miles away. It may be of serious import- 

 ance to determine his distance : either for laying his course 

 along the coast or the making of harbour. He sees the 

 distant flash and he knows it is safe to stand in till he hears 

 the bell. Presently he picks this up. He now waits for the 

 next group of flashes and he counts them as they come in : — 

 one, two, three .... till he hears the clang of the bell. It 

 may come with the 15th flash. If so he knows he is 15 

 cables or 1^ mile distant. Nothing can be simpler. As 

 mere indicator of direction the light- and-bell buoys of our 

 coasts possess nothing like the value of this synchronized 

 light-and-bell buoy. The first cost would be small and the 

 cost of upkeep, compared with that of a lightship, trifling. 



Modern advance has given us signals of other kinds which 

 — as all know — have already afforded invaluable help to the 

 sailor. Wireless is a sort of light signal against which fog 

 and snow and thick weather are powerless. Its velocity of 

 propagation is practically instantaneous. Submarine sig- 

 nalling utilizes the propagation of sound through water, and 

 this may be regarded as furnishing a sound signal which 

 also is unaffected by weather conditions. The sound of a 

 bell-stroke beneath the water travels at about 4800 feet 

 (1463 metres) per second. Hence the submarine bell- 

 stroke lags behind the wireless "dot" by 1*2 seconds for 

 each nautical mile traversed, if both signals are started 

 together. If an air-sound and a water-sound be started 

 synchronously from the same point, the lag of the atmospheric 

 sound on the submarine is 4'3 seconds for each nautical mile 

 traversed. 



For the benefit of those unacquainted with recent advances 

 in this branch of applied science a word may be said here 



