ATMOSPHERE AND THE ACOUSTIC EFFICIENCY OF FOG-SIGNAL MACHINERY. 247 
also for placing at the writer’s disposal the manuscript of a memoir dealing with the 
mathematical theory of his sound-measuring instruments. To the Postmaster- 
General of Canada, the Hon. L. P. Pelletier, the writer is indebted for permission 
to take up permanent quarters on board 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 station a few miles away. The writer 
wishes to testify to the unfailing courtesy of Capt. J. B. Pouliot and officers of the 
“ Lady Evelyn ” in carrying out these tests, and their willingness to co-operate in 
bringing them to a successful conclusion. For the loan of surveying instruments and 
valuable assistance in constructing charts of the locality, the writer wishes to 
thank Commander C. Savary of the Hydrographical Survey Ship “ Cartier.” To 
Mr. H. H. Hemming the writer is indebted for invaluable assistance in taking 
observations during the entire month during which the experiments lasted. 
Finally, the writer wishes to express his deep obligation to Prof. H. T. Barnes, 
F.R.S., Director of the Macdonald Physics Building, not only for placing the 
resources of the laboratory at his disposal for the work, but in kindly offering to 
bring to the attention of the Canadian Government the importance of this field of 
research. As a result, facilities for carrying out the tests at Father Point were 
generously provided for on a very liberal scale by the Department of Marine and 
Fisheries. 
[Note added February 14, 1919.—Fog-signal tests were carried out at Father Point in September and October, 1917, 
under the auspices of the Canadian Honorary Advisory Council for Scientific and Industrial Research. A detailed account 
of the results obtained is to be published in a Report, copies of which may be obtained from the Secretary of the above 
Council, Department of Trade and Commerce, Ottawa, Ontario. 
In the course of these tests a thorough investigation was made of the thermal method of mea suring the acoustic output 
of a small diaphone sounding a continuous blast. Temperature differences were measured by means of a pair of thermo¬ 
elements inserted, one on the high-pressure side of the vibrating piston, the other on the low-pressure side. Almost 
continuous temperature readings were recorded as the air-pressure was allowed to fall gradually from 29 to 6 pounds per 
square inch; the corresponding acoustic outputs were found to be 350 and 100 watts respectively, while the acoustic 
efficiencies were eight per cent, at the higher pressure and 24 per cent, at the lower pressure. Several series of observations 
with and without the trumpet confirmed these results which, taken in conjunction with those obtained from the 1913 tests 
on a large diaphone, indicate that higher efficiency and greater atmospheric penetration in fog-signal apparatus may be 
predicted by the utilization of low air-pressures and by the separation of a single source of sound into a number of small 
synchronized units. 
With the co-operation of Prof. Dayton C. Milleb of the Case School of Applied Science, Cleveland, Ohio, U.S.A., notes 
from the large and small diapliones were recorded in permanent form as sinuous lines on photographic films, making use of 
the “phonodeik,” a description of which will be found in the inventor’s recent book “ The Science of Musical Sounds,” 
(Macmillan & Co., New York, 1916). Records were obtained to distances of nearly three miles, and their analysis brought 
out a number of interesting and important facts. It was found that the sound from the small diaphone, provided with a 
detachable trumpet, was extremely complex. From records taken with and without the trumpet, it was inferred that the 
effect of a resonator of correct design would be to concentrate a greater proportion of the total acoustic output into the 
master tone. The records obtained at various distances from the large diaphone indicate that the high overtones do not 
travel far, but are filtered out by the scattering action of atmospheric eddies. As the master tone alone survives to an 
appreciable extent at distances greater than two miles, it is obvious that the object of the designer of fog-signal apparatus 
should be to concentrate the greatest possible amount of energy into the master tone. From the harmonic analysis of the 
phonodeik records it is now possible to obtain accurate data as to the relative proportions of energy contained in the master 
tone and in the overtones.] 
