I9OI-2 TRANSACTIOKS. 59 



ligation proved that it was sounding as loudly as ever, the 

 trouble being with atmospheric conditions. Some of you 

 may have noticed echoes produced where there was apparent- 

 ly no hill or surface to reflect the sound. These echoes must 

 have been reflected from strata of air differing greatly in 

 density from that at the point of production of the sound, 

 and are one example of the difficulties that fog alarm signals 

 strive in vain to overcome. For these reasons we warn 

 mariners that they must never judge tlieir distance from a 

 fog signal either by the power of the sound or by the absence 

 of sound, because under certain conditions of atmosphere the 

 sound may be heard loudly at long distances from the alarm ; 

 under other conditions it may be lost at a very short distance, 

 and these conditions may vary at the same siation within very 

 short intervals of time or of space. Unfortunately it seems 

 impossible to convince captains of this, and many wrecks 

 have resulted from their ignorance of these well known aber- 

 rations. 



Lightships. Danger signals that have been greatly im- 

 proved in recent years are floating aids to navigation, includ- 

 ing lightships and buoys. The modern lightship is a reser- 

 voir of complicated machinery, containing apparatus for 

 revolving lights at the mast head; powerful fog signal machin- 

 ery; auxilliary power for propelling the vessel, in case she 

 breaks away from her moorings or is obliged to run for shelter, 

 and mechanical appliances for relieving the strain on the 

 anchor in heavy weather. A lightship, however, can in no 

 way be considered as satisfactory an aid to navigation as a 

 solidly founded lighthouse, because the motion of the waves 

 prevents the light from being seen at a great distance, and in 

 our climate a vessel must leave her station when ice forms, 

 and is, therefore, unavaila-ble at the time navigation is closing, 

 when an aid is most urgently required ; moreover she is liable 

 at any time to break from her moorings, and may therefore 

 not be fouud at the place expected. The one point in favour 

 of a lightship is that her station may be so located that 



