Max Kohl. Chemnitz. 



37 





3. Helmholtz's Double Syren. 



(Fig. 3.) 



The double syren is particularly 

 adapted for ascertaining the number 

 of vibrations producing certain notes 

 and for experiments on harmonics, 

 beats and combination notes. The 

 ratch of the train of wheels is fitted 

 with electrical contact which con- 

 nects it with an electrical second 

 pendulum clock. 



4. Timing Apparatus for 

 producing Lissajous' Curves. 



(Fig. 4.) 



r ^ The tuning forks have excellently 

 ground and polished steel mirrors 

 attached to their limbs and one of 

 the forks is intoned by electro-mag- 

 netic means. The following acces- 

 sories are supplied with the apparatus. 

 2 tuning forks in C = 256 oscilla- 

 tions, 



1 F = 170 2 / 3 

 1 = 512 



The apparatus is very suitable 

 for demonstration on the screen. 



5. Portable Reflecting Galvanometer with Ocular Scale according 

 to Prof. Weinhold. (Fig. 5.) 



The ocular of the telescope attached to this instrument is provided 

 with a transparent scale. A small mirror placed at the side of the 

 ocular throws a pencil of light upon a reflecting prism fixed to the 

 scale whence it passes to the telescope objective. The telescope is 



