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( THE FOOTPRINTS OF SOUND. BV FRANK M. DEEMS. M. D.. PH. V CCOM PAN VING this ar- tide is a picture of the footprints of sound: in this case, of articulate speech. Does the phrase seem a fanciful one? If so, be assured that the picture represents not only the footprints of sound, but the shadows of an echo as well. In other* words, it is a micro-photograph-of a record—a phonogram taken from an Kd- ison phonograph cylinder. For the benefit of such readers as are not familiar with Mr. Kdison's wonderful tone-recorder, let me explain in detail, step by step, how this pic- v_ • Fio. i . 4 ture was produced. Hut before so doing I will draw a parallel between the phorograph and the human ear. I'p to a certain point there is a striking similarity between the mechanical construction of the phonograph and the structure of the human car. This will be better shown bv a reference to the • acc unpanying diagram of the ear (Fig. i). The outer ear is funnel-shaped; it is, in fact, a natural hearing - trumpet. '1 his serves the purpose of collecting the vibra- tions of the atmosphere which constitute sound, condensing and conducting it. In the phonograph there i> a corresponding funnel for the same purjxjstf. At the l»ot- tom of the outer car • funnel there is a membrane, a beautiful structure a little thicker than gold-beaters’ skin. This is the tympanum, or, as it is more commonly called, the 44 drum of the ear.” At the l>ot- tom of the phonograph speaking-tube! and corresponding exactly to the ear-drum, there is a small circular piece of thin micro- scopic cover-glass called the diaphragm. In, the car there is attached to the inner sur- face of the ear-drum a movable chain of three small tones, called the 44 hammer,” the 44 anvil,” and the 44 stirrup,” from their close resemblance to the objects above men- tioned. These three little bones are so ar- ranged and connected that we may regard them, as a whole, as a compound lever auto- matically operated by two small muscles. This chain of l>oucs serves a double pur- pose: it keeps the ear-drum gently on a stretch, but delicately adjusting it to each varying impulse with which the air comes laden, tightening it so that it thrills to every whisper, loosening it against the injurious effects of sounds too loud. Hut they serve a yet more important purpose : they receive the vibrations from the ear-drum to which they are attached, and convey them cross the cavity of the inner ear to the nervous expansionsof the auditory, or hearing nerve. In the phonograph the part corresponding to this chain of tones is called the stylus, or engraving jien. It consist of a little hinged lever cemented to the under surface of the thin glass diaphragm. It is tipped with a point of sapphire. This sapphire point, be- ing exceedingly hard, never loses its shape or polish by wearing away, or from corro- sion. It is not necessary to go into the com- plicated but wonderfully beautiful arrange- ment of the auditory nerve: suffice it to snv, that in the phonograph the wax cylinder takes the place of the nerve and brain. So. we see, there is really a close analogy bc- i