154 .SEC. 6. SOL'ND. 



712. Savart's Toothed Wheels. A set of wheels, of 

 different sizes and numbers of teeth, to produce a succession of 

 notes. Elliott Brothers. 



713. Sonometer, with sound-post on the principle of the 

 violin. Also adapted for passing the galvanic current through 

 strained wires. Dr. Stone. 



714. Metronome, invented by Dr. Wollaston. 



G. If. Wollaston) Esq. 



715. M. le B,oux's Apparatus, for determining the velo- 

 city of sound. Conservatoire des Arts et Metiers, Paris. 



716. Phonometer. Prof. Lucae, Berlin. 



The phonometer, " speech-scale," is intended to determine accurately the 

 intensity of speech, that is to say, the pressure of expiration employed in 

 speaking. 



The apparatus consists of a short metal tube, one end of which expands 

 in the shape of a funnel to a kind of mouth-piece, whose hrim is coated with 

 gutta-percha. , At the other end of the tube is attached a contact lever 

 oscillating in an axis, the lower section of which lever is formed by a round 

 aluminium plate, which, when in a state of repose, that is to say, at the 

 vertical position of the contact lever, closes the tube, whilst the upper end of 

 the contact lever, terminating in a point, indicates on a quadrant the oscilla- 

 tions of the pendulum. By any word which is spoken into the mouth-piece, 

 the plate will be pressed outwards according to the pressure of the air 

 employed. A spiral spring attached to the axis has the effect, that by dis- 

 continuing speaking the contact lever remains stationary in the maximum of 

 the motion transmitted to it, and its inclination can be read on the quadrant. 

 The practical use of the instrument in the first instance is, to determine when 

 speaking in a loud or a low voice the relative intensity of one and the same 

 word, or, rather, the preponderating sound prominent in the word uttered, 

 and imparting to it the greatest colour. This object the apparatus perfectly 

 accomplishes, since the force of the utterance is proportional to the density 

 of the air effected in the tube. The apparatus consequently admits, among 

 other things, of a more exact test of hearing with persons slow of hearing than 

 has been the case hitherto with ordinary speaking. 



716a. Phonoptometre, by M. Lissajous. 



M. J. Duboscq, Paris. 



716b. Experimental Windchests, for measuring the effect 

 of heat on reeds. Dr. Stone. 



III. ANALYSIS AND SYNTHESIS. 



717. A series of Chladni's Figures. 



Prof. Frederick Guthrie, F.R.S. 



Sand being scattered on a square brass plate, clamped in the middle 

 and horizontal, the plate is bowed at various points of its edge, while 

 various other points are touched with the finger. The sand is accumulated 

 in the lines of least motion or nodal lines. Gummed paper is then pressed 

 upon the figures so formed. 



