250 PHYSICS. 



ing the refraction of sound-waves. In an inverted bell-jar of glass is 

 placed a horizontal disk of smoke-blackened paper. A circular collo- 

 dion membrane is arranged above it, inclined 33° to the plane of the 

 edge of the bell. If now on the axis of this membrane, and at 13 centi- 

 meters distance, an electric spark be produced, the membrane vibrates 

 and the waves which it jjroduces make a series of concentric circles upou 

 the paper, the center of which is on the axis of the membrane. If the 

 bell be filled with carbon dioxide the center of these circle^' is displaced 

 in the direction required by refraction and by a quantity corresponding 

 to the sonorous refractive index. Hydrogen gas may also be employed. 

 — {Ann. Phys. Ghem., II, viii, 64:5, 1879.) 



Eood, in studying the action of a revolving fan introduced into melo- 

 deons for the purpose of producing a " tremolo" effect, ascertained that 

 the variations in loudness produced by it were due to reflection or non- 

 reflectiou from the face of the revolving fan, and that the same effect 

 could be obtained from a disk consisting of closed and open sectors and 

 revolving in its own plane. With this simple apparatus the following 

 points were established: (1) At a perpendicular incidence the short 

 sound-waves are more copiously reflected than those that are longer, and 

 the regular reflection is more copious from large than from small sur- 

 faces. (2) When the sound-waves fall upon small flat surfaces at an 

 acute angle, the reflection is most copious in the same direction as with 

 light, but the reflected and inflected waves can be traced all around the 

 semicircle. (3) Qualitative comj^arisons between the power of different 

 substances to reflect sound can easily be made. (4) If a composite sound- 

 wave falls on the rotating disk, the shorter waves will undergo regular 

 reflection more coj)iously than the other comj)ouents. (5) The reflection 

 of sound from very small surfaces is easily demonstrated. — {Am. J. Sci., 

 Ill, xix, 133, February, 1880.) 



Ehodes has devised a sim^ile ai^paratus to aid the deaf in hearing, 

 called the audiphone. It consists of a thin flexible sheet of hard ebon- 

 ite rubber, provided with a handle like a palm-leaf fan, and with a cord 

 which can be tightened at pleasure to curve it into the form of a semi- 

 cylinder. The edge of the sheet is pressed against the upper set of 

 teeth, the convex surface being outwards, so that vibrations impinging 

 upon the sheet are transmitted through the teeth and bones of the skull 

 to the auditory nerve. Its use, therefore, is limited to cases where the 

 nerve is nearly or quite intact. Colladon has replaced the costly ebon- 

 ite by a sheet of fine elastic cardboard, about 18 inches by 10, and var- 

 nished at the edges, which is curved by being pressed against the teeth 

 by the hand. Experiments made with it upon deaf-mutes were highly 

 interesting. A professional musician, deaf for fourteen years, was en- 

 abled by this audiphone again to hear piano music. Fletcher, in further 

 experimenting, prefers birch-wood veneer cut to an oval 12 by 8 J inches, 

 steamed and bent to a curve. It is held between the teeth. In his ex- 

 perien(;e any audiphone is a failure in two-thirds of the cases of deafness 

 in whhih it is tried.— {Nature, xxi, 426, 469, 515, 1880.) 



