ADDRESS OF PROF. A. M. MAYER. 499 



alike in fluidity — will in equal times flow out of an orifice in the 

 bottom of a vessel. Henry found that equal quantities of mercury 

 and water flowed out of the vessel in equal times ; but with 

 different oils the times of flow of equal quantities were different. 

 Thus the rapidity of flow of sperm oil exceeded that of lard oil in 

 the ratio of 100 to 167. I think that this method of experimenting 

 suggested itself to Henry about fifteen years ago. I remember 

 when he was working with this apparatus, and of his telling me that 

 to his surprise he found that alcohol was less fluid than water. 



Henry always took a deep interest in the study of acoustics. His 

 additions to this branch of knowledge were chiefly the results of his 

 experiments in connection with our system of coast fog-signals. He 

 made extensive experiments on various sound-producing instru- 

 ments, such as bells, cannon, steam whistles, and steam reed and 

 syren fog-horns. He eventually decided in favor of the latter as 

 the most powerful and eflfective instrument yet invented. He 

 determined that these instruments send their sounds to the greatest 

 distances when they emit a note in the treble part of the musical 

 scale. They are, in fact, tuned very near to the treble C. Henry 

 also showed the uselessness of applying reflectors to these instru- 

 ments. But his principal researches were in the direction of 

 determining the influence of various atmospheric conditions on the 

 audibility and manner of propagation'of the sounds of the fog-horns 

 on our northern coasts. The results which he reached, though of 

 great importance, appear to bear a very sniall relation to the great 

 amount of time spent and fatigue and exposure endured in procuring 

 them. 



During eleven years Henry did not cease to labor most devotedly 

 to do all he could to advance the efficiency of our fog-signals by 

 studying the action of these instruments in all kinds of weather. 

 Many facts were collected, and very puzzling were these to explain 

 by any known laws pertaining to the propagation of sound. Thus 

 it was observed that a sound coming, to the mariner against the 

 direction of the wind would cease to be audible on the deck of his 

 vessel, while it continued to be heard to a listener on the mast-head. 

 An observation made at Block Island showed this fact in a marked 

 manner. The lens of this light is about 200 feet above the beach 



