1874] WRITINGS OF JOSEPH HENRY. 403 



Another question which naturally arises, but which has 

 not yet been definitely settled by experiment, is whether 

 both the siren and the whistle would not — equally with the 

 trumpet, give more efficient results when worked by con- 

 densed air than by steam. 



From hypothetical considerations this would appear to be 

 the case, since the intensity of sound depends upon the 

 density of the medium in which it is produced; and as the 

 steam is considerably lighter than air, and as the cavities of 

 all of these instruments are largely filled with steam, the 

 intensity of sound would on this account seem to be less 

 than if filled with air. 



At the conclusion of the experiments at Sandy Hook, the 

 siren was adopted as a fog-signal, in addition to the reed- 

 trumpet and the locomotive-whistle, to be applied to the 

 more important stations; while large bells were retained for 

 points at which fog-signals were required to be heard at but 

 comparatively short distances. These instruments of the 

 first class being adopted, it became of importance to deter- 

 mine — in actual practice, the cost of maintenance, the best 

 method of working them, and any other facts which might 

 have a bearing on their use. 



But as investigations of this kind would require much 

 time and peculiar advantages as to location and mechanical 

 appliances, this matter was referred to General J. C. Duane, 

 the engineer in charge of the 1st and 2d light-house dis- 

 tricts, who had peculiar facilities near his residence, at Port- 

 land, Me., — in the way of workshops and other conveniences, 

 and who from his established reputation for ingenuity and 

 practical skill in mechanism, was well qualified for the 

 work. The assignment of this duty to General Duane by the 

 Light-House Board was made during my absence in Europe, 

 in 1870, and as my vacation in 1871 was devoted to light- 

 house duty in California, I had no opportunity of conferring 

 with him on the subject until after his experiments were 

 completed. His results are therefore entirely independent of 

 those obtained under my direction, and I give them herewith 

 in his own words, with such comments as they may suggest, 

 and as are necessary to a proper elucidation of the subject. 



