ATMOSPHERE AND THE ACOUSTIC EFFICIENCY OF FOG-SIGNAL MACHINERY. 255 
it is difficult to forecast the relative intensities of the overtones produced in the trumpet from data 
relating to the characteristics of conical resonators tested in the laboratory.* The form of trumpet 
actually used (for dimensions see under fig. 1, §9) was that giving the greatest atmospheric penetration 
as determined by a large number of trials carried out at Father Point in 1903 under the direction of 
Lieut.-Colonel W. P. Anderson, Chief Engineer of the Canadian Department of Marine and Fisheries. 
As is well known, the energy of the sound-waves is dissipated largely owing to the effect of eddies in the 
atmosphere. According to the mathematical theory developed by Taylor (discussed in Section 12), the 
coefficient of extinction is proportional to the square of the frequency. It follows that overtones in the 
diaphone note will be much more rapidly extinguished than the fundamental. It is thus important in 
fog-signal apparatus that as much of the acoustic output as possible be concentrated in the fundamental, or 
“ master tone.” 
The rapid extinction of overtones with increasing distance from the diaphone was repeatedly observed 
during the tests carried out by the writer. At a distance of about 1000 feet the note was, as far as could 
be judged by ear, very nearly a pure tone. 
The phonometer, when correctly tuned, enables us to measure in C.G.S. units the pressure amplitude 
in the fundamental, and the readings given in Appendix II. must be interpreted in this way. As regards 
the carrying power of the signals it is the energy contained in the fundamental which is by far the most 
important. 
It is highly desirable in fog-signal tests that the dependence of attenuation on wave-length be studied 
in the light of Taylor’s theory, and that observations be carried out on the quality of the note at 
varying distances, as is now possible by the use of Miller’s “ phonodeik.”f 
Appendix II.—ACOUSTIC SURVEYS IN THE NEIGHBOURHOOD OF THE FATHER 
POINT FOG-SIGNAL STATION. 
(i.) General Procedure in Taking Observations. 
The object of the acoustic surveys carried out at Father Point was to obtain on different days and 
under varying meteorological conditions a permanent record of the distribution of sound in the neigh¬ 
bourhood of the same fog-signal station. For this purpose the Webster phonometer described in 
Appendix I., was found to satisfy the exacting conditions required of a robust and portable instrument 
sufficiently sensitive to respond to the minute changes of pressure occurring in sound-waves of ordinary 
loudness. 
Through the courtesy of the Department of Marine and Fisheries, permission was given to operate the 
diaphone at will for the purpose of the tests. Through the kindness of the Postmaster-General, the 
writer was authorised to take up permanent quarters on the mail tender, “ Lady Evelyn,” stationed at 
Rimouski, and to make use of .this ship in carrying out acoustic surveys in the neighbourhood of the 
Father Point signal, a few miles away. Mr. LI. H. Hemming,! B.A., assisted in the tests and proved 
himself invaluable in taking observations. As a matter of regular routine an acoustic survey was carried 
out whenever possible during the forenoon. The ship was skilfully navigated over a series of courses 
under the guidance of her commanding officer, Captain J. B. Pouliot. Although the usual weather 
records were kept at the Father Point meteorological station, it was found necessary, as far as available 
instruments allowed, to take independent observations from the ship, as air temperatures, wind velocities 
and directions even half a mile from shore were observed to differ considerably from those on land. 
* As determined by Milleb, D. C., in connection with the development of the “ phono deik.” (‘The Science of Musical 
Sounds,’ 1916, p. 156, et seq.) 
f See footnote, p. 247. 
J Now Capt. H. H. Hemming, of the Third Field Survey Company, on active service in France. 
