A Summary of Researches in Sound; Conducted in the Service of the United States Light-House Board

Purchase of this book includes free trial access to www.million-books.com where you can read more than a million books for free. Excerpt from book: Section 3' -. . From the result of this table it would appear that the sound can be heard moving at right angles to the wind better at an elevation that at the surface?a result not anticipated. OBSERVATIONS ON THE EFFECT OF WIND ON SOUND. This series was commenced on the 2d of September. Barometer, 30.3 inches; thermometer, dry-bulb, 70.5 F. wet-bulb, 67.5. Wind at the surface of sea was six miles per hour, and variable; at 3 p. m. the velocity was eight miles at the surface. (See Fig. 7.) Fir: . 7. The experiments were made by means of the steamer Mistletoe, which proceeded from the light-house, as a center, in different directions, blowing the whistle every half-minute, and returning when, from a signal, the sound was lost; the time being noted by different observers, and the distance estimated by the position of the steamer in reference to known objects on the Coast-Survey chart, as well as by angles of azimuth and time of sailing. The steamer was directed to proceed, as indicated in Fig. 7, 1st, against the wind, so that the sound would come to the observers with the wind; 2d, at right angles to the wind; 3d, in an intermediate direction between the last course and the direction of the wind; 4th, approximately with the wind, so that the sound would come to the ears of the observers against the wind; 5th, in an intermediate direction; and, 6th, again at right angles to the wind. It wassupposed that by this arrangement a symmetrical curve of sonnd would be obtained; and we think this would have been the case had the wind remained constant in direction. It did remain nearly the same during the time of describing the first, second, and third courses, and only slightly varied during the fourth; but previous to running the fifth and sixth courses the wind had changed to a direction nearly at right..