III. ANALYSIS AND SYNTHESIS. 183 



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 Francis Wollaston. 



G. H. Wollaston. 



716. Phonometer. Prof. Lucae, Berlin. 



The phonometer, " speech- measure," 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, the rim of which is coated 

 with india-rubba. The other end of the tube is attached to a contact 

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

 aluminium plate, which closes the tube when the lever is in a vertical 

 position and in repose, whilst the upper end of the contact lever, terminating 

 in a point, indicates on a quadrant the oscillations 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. When speaking is discon- 

 tinued a;spiral spring attached to the axis has the effect of suspending the 

 action of the lever at 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 utterance 

 is proportional to the density of the air effected in the tube. The apparatus 

 consequently affords, among other things, 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. Series of Chladni's Figures. Frederick Guthric. 



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 ringer. The sand is accumulated 

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

 upon the figures so formed. 



