158 SEC. 6. SOUND. 



By placing the weight with the annotation upon the spot indicated with x 

 on Lamella I. the oscillations are as 1 : 4 (double octaves). 



The two smaller weights of different size serve for the more exact regula- 

 tion in case great changes in the temperature, or simultaneous oscillation of 

 either one or the other of the tables, should be of injurious influence. 



Lamella II., as has been observed at the commencement, can be turned 

 about an horizontal axis, so that its vibrations can be adjusted either rectan- 

 gularly, parallel, or in any angle whatever to Lamella I. In case it is neces- 

 sary to ease and screw fast the hexagonal nut, the key is added for the purpose. 

 The small key is for unscrewing and fastening the screws which fix the 

 Lamella. 



724. Melde's Wave Apparatus, for showing the produc- 

 tion of Chladni's figures of sound, according to the theory of 

 Wheatstone. 



{See PoggendorfFs Annalen, Jubelband, p. 101, and the 

 accompanying description.) Ferdinand Suss, Marburg. 



This apparatus has been more particularly described by Professor Melde, in 

 Poggendorff's Annalen, Jubelband, page 101. 



The present specimen is distinguished by several differences from that de- 

 scribed in the above-mentioned work, so that the manipulation is considerably 

 facilitated, but before entering into this, it must be mentioned that in the con- 

 struction of this apparatus it was kept in view that two systems of waves of 

 equal length and equal intensity pass swiftly through a square plate. 



The upper system of waves is formed of 33 rows of 17 netting sticks each, 

 which together make two wave lengths. The saddle upon which the netting 

 sticks are placed corresponds to a length of 1 5 of wave lengths ; it has on 

 two sides (above and below) wave-systems, which in so far differ from one 

 another, as the one is like a system of two mountains with one valley in the 

 middle, and the other like two valleys intersected by a mountain. On the 

 longitudinal sides of this saddle rectangular zinc plates have been screwed on, 

 which are provided with divisions for adjusting the desired phases. 



O denotes the centre position (middle between mountain and valley). The 

 lines marked on the black board correspond to the waves formed by the netting 

 sticks. The longitudinal line serves as index upon which the lines of the 

 saddle are indicated. 



When the saddle has been adjusted in the desired position, the board is 

 lifted by the handles fastened on the sides as far as possible perpendicularly 

 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 handles 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. Muller. 



T. W. Albert, Frankfort-on-thc- Maine. 



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

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



