No. 52141. 



Foucault Pendulums, Harmonic Motion, Resonance. 



299 



52 137. 1 : 6. 



52 131. 1 : 3. 



52 140. 1 : 10. 



52138. 1:14. 



52 139. 1 : 6. 



.".I 1 , i:;,s. Apparatus for projecting harmonic vibration (sine vibration), as suggested by Hofler, 

 Figure (Hofler, Physik, Figs. 30 and 243; Hofler-Poske, Figs. 12 and 144) . . . 

 For demonstrating the composition of two sine vibrations, two of the above apparatus and two 

 projectors are necessary. 



52.139. Resonance Top (van Schaik's), Figure (Ztschr. f. d. phys. u. chem. U., 7, 1893/94, 

 p. 181). Price, exclusive of vice 



The top is loaded on one side and produces considerable vibration, according to the free length 

 of the spring, and at high or low speed. 



52.140. Resonance Top (Frahm's), Figure (Glaser's Ann., Vol. 59, 1906, pp. 697 et seq.) 



The rotating disc of the top is loaded on one side, so that the top when held in the hand makes 

 a considerable amount of vibration. A so-called Frahm comb with six spring tongues is fixed to tin- 

 top, these tongues having different numbers of vibrations. With decrease in the number of vibrations 

 one spring after another vibrates. 



The principle is used in speed measurements on prime movers, and when the tongues are electri- 

 cally excited by means of an A. C. magnet, it can also be applied to frequency measurements. 



52.141. --idem, in velvet case 



For use with the projection apparatus. 



s. d. 

 2. O.-O 



1. 2.0 



2. 5.0 



2.10.0 



Cl. 633, 3751. 3785. 

 3K-5, 5446, 3947. 



