156 SEC. 6. SOUND. 



The round bars serve for the production of oscillating curves of two ellip- 

 tical vibration movements. 



Finally, it is to be observed that the apparatus may be used equally well 

 for fixing the vibration curves, for which purpose a phonautograph is em- 

 ployed, the cylinder of which is covered with a paper, as smooth as possible, 

 on which soot is laid, but not too thickly. 



A small piece of the top of a feather fastened with wax upon one of the 

 smaller Lamellae will be sufficient to describe the curves. In this case, the 

 oscillating surfaces ought to be parallel. 



721. Atlas, belonging to the same, illustrative of the theory 

 of oscillating curves, by Dr. F. Melde. 



Ferdinand Suss, Marburg. 



722. Melde's Tuning-fork Apparatus for producing 

 stationary waves on a thread. 



(See Poggendorff's Annalen, vol. 109, p. 193 ; and vol. Ill, 

 p. 513.) Ferdinand Suss, Marburg. 



In Poggendorff's Annalen, Vol. CIX, p. 193, and Vol. CXI. p. 518, this 

 apparatus is described more in detail, as well as several experiments which 

 were made with the same, and likewise the theory of the oscillation curves, 

 (" Lehre von den Schwingungscurven ") by Dr. Franz Melde, p. 94. 



By means of a little sliding rod (a little glass stick) which is screwed into 

 one of the prongs of the fork, and rubbed with wet fingers, the tuning-fork is 

 brought into a state of vibration. (The little glass stick, owing to its fragility, 

 must be inserted reversely into the wooden frame, when not used, so that only 

 the brass-neck of it is visible. On the lower part of the tuning-fork there is a 

 tunable pin, which takes up one end of the thread, and which at the same 

 time serves for stretching the thread. From this point the thread passes 

 through the small neck of the other prong of the fork to the clamp, which can 

 be moved forwards and backwards on the bar, which is about a meter long, 

 and thus allows up to this limit any length of the thread to be fastened. In 

 order to read the length of the thread, there is on one of the narrow sides of 

 the bar a division indicating half centimeters. 



The tuning-fork can be turned about its vertical axis in such a way that its 

 oscillation surface falls in a parallel line with the longitudinal direction of the 

 thread, as well as perpendicular to this, or in any other selected angle. 



The bar can be turned about a horizontal axis, and arrested in any desired 

 position by means of the nut of a winged screw fixed at the back, so that the 

 thread can form any desired angle with the longitudinal axis of the tuning- 

 fork. 



It requires but little practice to effect such a tension of the thread that the 

 required number of waves always appears. 



723. Melde's Apparatus for the Combination of Two 

 Thread-vibrations. 



(See Melde's Lehre von den Schwingungs-curven, p. 99.) 



Ferdinand Suss, Marburg. 



723a. Melde's Apparatus for the production of Oscilla- 

 ting Curves of two Rectilinear Thread Vibrations on a 

 Strained Thread. 



The apparatus consists of two principal parts, one of which is a Lamella, 

 oscillating vertically, fastened on a pedestal, and which is set in oscillating 

 motion by an electro-magnet. The Lamella itself forms the interference. 



