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I V. On the Propagation of Sound in the Free Atmosphere arid the Acoustic 
Efficiency of Fog-Signal Machinery: An Account of Experiments Carried 
Out at Father Point , Quebec , September , 1913. 
By Louis Vessot King, MA. {Cantab.), D.Sc. {McGill), Associate Professor of 
Physics, McGill University, Montreal. 
Communicated by Prof. Howard T. Barnes, F.R.S. 
[Plate 1.] 
Received May 11,—Read June 14, 1917. 
Contents. 
Part I. —On the Mathematical Theory oe the Propagation of Sound in a Homogeneous 
Atmosphere with Special Reference to Waves of Large Amplitude. 
Section. Page 
1. Introduction..'.212 
2. Plane waves of small amplitude.213 
3. Spherical waves of small amplitude.214 
4. On the efficiency of sound-producing instruments.215 
5. Sound-waves of finite amplitude— 
(i.) Note on results of previous investigations.217 
(ii.) On a contribution to the theory of the propagation of aerial plane waves of finite 
amplitude . 219 
(iii.) Application of the preceding theory to the generation of finite waves by the 
harmonic motion of a piston.221 
6. On the thermodynamic basis for the measurement of the acoustic output of a compressed 
air siren.223 
7. On the theoretical calculation of the characteristics of finite waves emitted by a compressed 
air siren. 225 
Part II.— On the Measurement of Sound Intensity and of the Acoustic 
Output of Fog-Signal Apparatus. 
8. Notes on previous fog-signal experiments ..227 
9. Description of the diaphone.229 
10. Note on the practical measurement of the characteristics of sound-waves.231 
11. Note on the Webster phonometer.232 
12. On the influence of meteorological conditions on the propagation of sound— 
(i.) Introduction.234 
(ii.) Discussion of the Father Point acoustic surveys.236 
(iii.) Note on atmospheric losses.237 
(iv.) Note on the effect of fog. .237 
(v.) Note on the determination of the direction of sound.238 
VOL. CCXVIII.—A 564. 2 F 
[Published April 23, 1919. 
