244 ON THE ATMOSPHERE AS A VEHICLE OF SOUND. 
INDEX. 
§ 1. Introduction 183 
§ 2. Condition of the Question 184 
§ 3. Instruments and Observations 186 
§ 4. Influence of Sound-Shadow. „ 190 
§ 5. Rotation of Horn 191 
§ 6. Contradictory Results 194 
§ 7. Aerial Reflection and its Causes ; solution of contradictions 194 
§ 8. Aerial Echoes 197 
§ 9. Experimental Demonstration of the stoppage of Sound by Aerial Reflection .... 202 
§ 10. Action of Hail and Rain 205 
§ 11. Action of Snow 207 
§ 12. Action of Fog. Observations in London 209 
§ 13. Experiments on Artificial Fogs 214 
§ 14. Observations at the South Foreland 216 
§ 15. Atmospheric Selection 220 
§16. Action of Wind 224 
§ 17. Influence of Pitch and Pressure 227 
§18. Concluding Remarks 228 
Appendix : — 
On Gun-flashes as Fog- signals 232 
Remarkable Instances of Acoustic Opacity 234 
Partial Summaries of Observations in Chronological Order 235 
Table of Ranges of Holmes’s Horns 243 
Syren and Horns 243 
