138 BULLETIN OF THE 



wave. From this last explanation, Professor Henry seems to have 

 receded before his death." 



Mr. Johnson said that he called attention to this statement, as 

 he was satisfied that Mr. Price-Edwards had permitted himself to 

 fall into some inaccuracy as to Prof. Henry's action in this matter. 

 It was within Mr. Johnson's personal knowledge that Prof. Henry, 

 up to the last, had considered the theory of the tilting of the sound 

 wave, under certain conditions, as a good working hypothesis. The 

 Professor had it in contemplation when he was called from his 

 labors to attempt the solution of certain of the questions connected 

 with this subject by stationing observers in steamers, around a 

 vessel anchored far enough from shore to be out of reach of land 

 echoes, on which a powerful fog-signal should be in operation, and 

 these observers should be aided by others in captive balloons, who 

 should note simultaneously with them, upon charts and tables pre- 

 viously prepared, not only the audibility of the signal, but all the 

 other data which could be obtained from the action of the ther- 

 mometer, the hygrometer, and the anemometer, as to the then con- 

 dition of the atmosphere. When all this information should be 

 tabulated, Professor Henry hoped to deduce something more of 

 the law of the movement of the sound wave under given con- 

 ditions, and to formulate it for the benefit of the mariner. This 

 was a work which Professor Henry had left to his successors and 

 which the speaker believed they would not neglect. 



Mr. Johnson then took up an article in the Annates des Ponts et 

 Chausses for October, 1880, by M. Emile Allard, Inspecteur General 

 des Ponts et Chausses, entitled Comparison de Quelques Depenses 

 Relative au Service des Phares en France, aux Etats- TJnis et en Angle- 

 terre, and called attention to that portion of it in which it was 

 stated in effect, that the lighted coast of the United States measured 

 about 7,500 nautical miles, and that the estimate of the Light- 

 House Board of the expense of maintaining the Light-House Ser- 

 vice for the year ending June 30, 1880, was $2,046,500, and that 

 hence the cost to the United States for lighting each nautical mile 

 of its coast was 1,293 francs, while that of France which had 

 twenty-five lights to the one hundred nautical miles [the United 

 States having but about nine lights to that distance] was but 1,155 

 francs. 



