IV. INTERFERENCE. 189 



Would be best fastened to a rotatory apparatus such as are used for 

 colour spindles, &c., and placed in front of a mirror. All waves, with the 

 exception of a horizontal one, should be covered by a black screen. 



730. Brass Tube, with Gas-burner, for Intonation. 



(Compare Poggendorff's Annalen, vol. 129, 1866.) 



Albrccht, Tubingen. 



731. Rotating Mirror, movable towards all sides. 



Albrecht, Tubingen. 



This mirror has not yet been described, but several specimens have already 

 been executed by Mr. Albrccht. That position of the mirror in which its 

 normal forms a moderate angle with the rotatory axis, is peculiarly adapted 

 to change the reflected image of the sonorous flame into a beautiful elliptical 

 crown. 



731a. Barlow's Logograph, an instrument for recording 

 pneumatic effects of speech, showing the consonant actions and 

 the vibratory effects accompanying vowel sounds. 



W. H. Barlow, F.R.S. 



731b. Apparatus for Synthesis of Vowel Sounds. 



Prof. Clifton, F.R.S. 



732. Apparatus for the projection on the screen of the 

 curves produced by the combination of rectangular vibrations. 



Yeates fy Sons. 



787a. Electro-Diapasons, showing the composition of vibra- 

 tory movements by producing fixed acoustic figures. 



M. Mercadicr, Paris. 



IV. INTERFERENCE. 



733. Apparatus for demonstrating, by the aid of flames, the 

 interference of two musical sounds. 



Prof. Dr. R. A. Mees, Director of the Physical Labora- 

 tory of the University of Groningen. 



The apparatus consists of two curved movable cross tubes, narrowed at 

 one end ; their narrow openings, being near each other, are tightly fixed in a 

 longer tube, also ending in a narrow opening ; this is placed close to a strong 

 flame, and also a very small flame, which can be seen in a rotating mirror. A 

 small movable burner for this small flame is attached to the apparatus. When 

 a sound-wave proceeds from the opening of tbe instrument, the strong flame 

 diminishes abruptly in length and begins to roar, while the small flame rapidly 

 vibrates, its motion being visible in the rotating mirror. The open ends of the 

 two curved tubes can be placed before the mouths of two unisonant organ 

 pipes, or above two different segments of a vibrating plate. When only one 

 of the pipes is sounded, the flames show the vibrations, but, when both pipes 

 are sounded, there is no agitation of the flames, the two sound-waves counter- 

 acting each other. When the two openings are above segments of the plate, 

 which are in the same phase of vibration, the flame is agitated, but, when they 

 are above segments in the opposite phase, the flame remains at rest. 



