Sound: A Course of Eight Lectures

But I will gladly move away from discussing "claims" of priority to the discussion of science itself. Included as a somewhat out-of-place addition in the report of Professor Henry Joseph Henry (1797–1878), an American scientist who served as the first Secretary of the Smithsonian Institution and chaired the U.S. Light-House Board. is a second report by General Duane James B. Duane (1824–1889), an officer in the U.S. Army Corps of Engineers who conducted extensive acoustic research for the U.S. Light-House Board., based on an extensive series of observations he made in 1870 and 1871. After clearly stating the points that needed to be decided, the General made the following remarks:

"Before giving the results of these experiments, I will state some facts that explain the difficulties in determining the power of a fog signal.

"There are six steam fog whistles on the coast of Maine. These have frequently been heard at a distance of twenty miles, yet just as often they cannot be heard from only two miles away—even when there is no noticeable difference in the condition of the atmosphere.

"The signal is often heard at a great distance in one direction, while in another, it can barely be heard at the distance of a mile. This is not caused by the wind, as the signal is frequently heard much further against the wind than with it.¹ For example, the whistle on Cape Elizabeth can always be heard clearly in Portland—nine miles away—during a heavy northeast snowstorm, even when a gale is blowing directly from Portland toward the whistle.²

"The most confusing difficulties, however, arise from the fact that the signal often seems to be surrounded by a belt—varying in radius from one to one and a half miles—where the sound seems to be completely absent. For instance,

¹ In other words, uniform air with an opposing wind is often better for carrying sound than non-uniform original: "non-homogeneous" air with a tailwind. We had the same experience at the South Foreland.—J. T.

² If this observation had been published earlier, I would have been delighted to refer to it in my recent writings. It is a striking confirmation of the observations I made on the Mer de Glace original: "Sea of Ice"; a large glacier on the northern slopes of the Mont Blanc massif in the French Alps. in 1859.