PHILOSOPHICAL SOCIETY OF WASHINGTON. 137 



was lost at a distance of about a mile, it was distinctly, though 

 faintly heard at Bonnet Point, distant one and one-half miles, and 

 that while it was lost completely at two miles off, on the run to 

 Newport, it was picked up at Fort Adams, three miles off, and 

 heard almost at its full power at three and one-fourth and three and 

 one-half miles away. These records were made by Lieut. Com. 

 F. E. Chadwick, U. S. N., Assistant Light-House Inspector, to 

 ascertain the facts, bearing on the statement that the fog-signal 

 stopped from time to time, made by those who had noticed these in- 

 termissions of audibility ; and the fact that the fog-signal was in 

 continuous full blast, was noted by his assistant, who remained at 

 Beaver Tail for the purpose. 



Mr. Johnson stated that this ricocheting of sound, these intervals 

 of audibility, ought to be recognized by the mariner, who should now 

 understand that in sailing toward or from a fog-signal in full blast, 

 he might lose and pick up its sound several times though no apparent 

 object might intervene. And the mariner now needed that science 

 should deduce the law of this variation in audibility and bring 

 out some instrument which should be to the ears what the mai- 

 mer's compass is now to the eyes, and also that variations of 

 this instrument yet to be invented, be provided for and corrected 

 as now are the variations of the mariner's compass. The speaker 

 referred to the benefit the mariner had derived from the prom- 

 ulgation of Professor Henry's theory of the tilting of the sound 

 wave up or down by adverse or favorable winds, and said that 

 by this the sailor had been led to go aloft in the one case and 

 to get as near as possible to the surface of the water in the other, 

 when trying to pick up the sound of a fog-signal. 



In this connection Mr. Johnson read the following extract from 

 an article entitled Signaling by Means of Sound, by E. Price-Edwards, 

 from the \_English~] Journal of the Society of Arts : 



"In one respect, however, the late Professor Henry, who was at 

 the time chairman of the United States Light-House Board, differ- 

 red from Dr. Tyndall, viz : in regard to the theory of acoustic 

 clouds, and their resultant aerial echoes. Professor Henry's ex- 

 planation of the obstruction of sound in clear weather, and the 

 echoes, is founded upon the asserted existence of upper and lower 

 currents of air, the tilting up of the sound wave, and the reflec- 

 tion of the sounds from the surface of the sea, or the crests of the 



