134 POPULAR LECTURES AND ADDRESSES. 



might be advantageously substituted for short 

 and long blasts of the steam whistle, but much 

 more advantageously short blasts of two sirens on 

 the same shaft, or on two shafts geared together, 

 sounding different notes, acute note for the short, 

 grave note for the long. 



70. HOLMES' RESCUE LIGHT. I shall conclude 

 by bringing before you (Fig. 16) an invention of a 

 most beneficent character. It is a light for life- 

 buoys, invented by Mr. Nathaniel Holmes, and 



FIG. 16. 



depending on the well-known property of phos- 

 phuretted hydrogen, to take fire when it bubbles 

 up from water. It is, I believe, contemplated by 



