From a seemingly frivolous incident, a few months ago, I was compelled to recognize the existence of a personal equation in attempting to determine the direction of the source of a sound; and I was able to determine with fair approximation the amount of my personal error, which knowledge I hope may be of service to me in approaching land or another ship.
I was in the country one evening, walking with a couple of friends. Approaching a pond we heard a certain noise and turned somewhat in that direction, at the same time commenting on the probable source. (I will not mention what the source was just now, for fear that no one would read farther). As we neared the water's edge, following a somewhat circling path, one companion pointed to an object in the dusk visible on the curb of the artificial pond as being the origin of the sound. But I felt positive that the sound came from a short distance to the left; and by turning my head alternately a little to the right and left of that direction I was able finally to fix upon an exact spot from whence it seemed surely to come. Then we approached cautiously until at a distance of about 12 feet, when the frog (!) jumped overboard; and the sound ceased with his disappearance. That settled the question and showed me that for some reason or other my appreciation of the direction of sound is in error by an angular distance which I carefully estimated to be about 10 degrees.
Without ever having thought out the reason, I realize that in seeking to determine the direction of a sound, one faces (involuntarily, perhaps) the approximate direction; and it is evident that the sense of appreciation of direction must be satisfied by so turning the head as to equalize the volume of sound in the two ears. It is upon this principle that the new invention, the submarine signal apparatus, has afforded ability to determine the bearing of a submerged bell; and this apparatus, by the way, is liable, through a difference in sensitiveness of the two transmitters, to an error similar in effect to what I am describing.
Now, in common probably, with many others who are at times exposed to blast effects of gun-fire, I am sensibly deaf in one ear—the right ear; as a natural corollary, in order to equalize the sound as conveyed to the brain through the two ears of different sensibility, the head would need to be turned from the direction of the source in such way as to bring the sound waves more directly to the less sensitive ear. In the homely instance which I have cited, my right ear was the weaker, and I had to face about 10 degrees to the left of that frog to equalize the effect.
If this seems puerile, I may say that I have on several occasions found amusement in verifying this personal error under different conditions, and find that I appear to be permanently in error that much. While the exactness of this error cannot be very pronounced, nor even very constant perhaps, I still think that a recognition of it may at times be useful in a subordinate way; and I advise men who are similarly affected to locate the true direction of a sound as being more or less to the right or left of the apparent direction, depending upon their partial deafness being of the right or the left ear.