188 SEC. 6. SOUND. 



so high, that the wires running parallel under the board catch into the hooks, 

 and so prevent the board from descending. 



In order to let the board and the saddle down again, a slight pressure with 

 the thumb on the pegs protruding from the board next to the handles, while 

 holding the bandies themselves firmly in their position, will be sufficient to 

 prevent the too rapid, or sideways, sliding down of the board. 



Finally, it is to be observed, that this apparatus can also very well replace 

 Eisenrohr's Interference Apparatus in so far as two waves will be sufficient'; 

 it would only be necessary to add a number of bars, or if entire surfaces are 

 desired, some saddles, the waves of which are of different and certain lengths. 



Great care is required by placing the one part of the apparatus upon the 

 other. 



725. Wave Disc, by Professor J. Miiller. 



J. Wilhclm Albert, Frankfort-on-the- Maine. 



The wave-disc by Prof. Dr. Joh. Mutter, Freiburg (Breisgau), is an 

 adaptation of the well-known stereoscopic disc (Phenakistoscope, or Wunder- 

 scheibe), for demonstrating the wave undulation. The eight drawings are 

 for the purpose of illustrating the water, rope, sound, and air waves, in CDvered 

 as well as in open pipes. 



See " Lehrbuch der Physik," VII. Edit. Vol. I., 155). 



726. Telephon, on Reis' system, for the reproduction of 

 sounds by galvanism. 



J. Wilhclm Albert, Frankfort-on-the- Maine. 



The telephon is based 011 the experiments of Wertheim and others re- 

 garding galvanic sounds. Philipp Reis, at Friedrichsdorf, made use of these 

 with a view of reproducing by means of galvanic action the musical sound; 

 produced by singing (or by pipes, &c. played upon), by employing an elastic 

 membrane and an interference apparatus constructed by him. 



(See Jahresbericht des physikalischen Vereins zu Frankfurt a Main. 

 Jahrgang 1860-61 ; also, "Muller's Lehrbuch der Physik, VII. edit. Vol. II., 

 135. 



727. Crank Apparatus, for showing the production of pro- 

 gressive waves in water, &c. 



Prof. J. Joseph Oppct, Frankfort-on-the- Maine. 



The rotating liquid molecules are represented by white wooden balls on 

 a black background, and are all put into motion by a crank attached at the 

 back. 



The whole shows two wave lengths. 



728. Cylinder Apparatus, for showing directly and com- 

 paratively, progressive and stationary waves of sound, and the 

 essential difference between them. 



Prof. J. Joseph Oppel, Franhfort-on-tlie- Maine. 



Contains H corresponding wave lengths on both cylinders. Other 

 drawings likewise, for example, with different wave lengths (for illustrating 

 the musical intervals, &c.), can be mounted on the cylinders, which are of a 

 somewhat conical shape. 



729. Two Wave Discs of paste-board for stroboscopic 

 illustration of a progressive and a stationary (water) wave. 



Prof. J. Joseph Oppel, Frankfort-on-the-Maine. 



