860 SEC. 19. EDUCATIONAL APPLIANCES. 



O9O. Teacher's Portable Lecture Set, for demonstrating 

 the principles of the science of Sound, comprising the following 

 apparatus : 



1. For demonstrating the mode of Propagation of Sound. 



Model to show propagation of wave by the oscillation of a 

 row of particles. The difference between the waves of 

 sound and light is shown by the production of both 

 simultaneously in close proximity. Row of marbles in 

 grooved board. 



2. For demonstrating the Necessity of a Conducting Medium. 



Air pump, 6-inch plate, with open receiver fitted with collar 

 and sliding rod. Small bell on cushion. 



3. For demonstrating the Reflection and Refraction of Sound. 



Tube, 2 inches diameter, and 6 feet long, with mouthpiece 

 and trumpet-shaped end ; pair of 18-inch tin reflectors ; 

 goldbeater's skin balloon. 



4. For demonstrating the Lengths of Waves, Regularity, Music, 

 and Noise. 



Tuning-fork, with steel points set in frame with groove 

 and smoked glass slides; whirling table with toothed 

 wheel and card and perforated disc ; Trevelyan rocker 

 and lead block. 



5. For demonstrating the laws of the Vibrations of Strings. 



Iron frame, with stretched piano wire to show need of 

 sounding board ; sonometer with four wires (two stretched 

 by keys and two by weights), graduated decimal scale, 

 movable bridges, paper riders, and extra strong bow ; 

 elastic cord, 15 feet long, with attachment for whirling 

 table. 



6. For demonstrating the laws of the Vibrations of Air-columns. 



C, tuning-fork and glass jar ; glass tube, 1 inch diameter, 

 2 feet long, open at both ends; set of 13 organ pipes 

 with bellows and wind chest ; pipe, with sliding stopper 

 for beats ; pipe, with glass slide and paper tray for show- 

 ing position of node ; metal reed pipe ; harmonium reed 

 large model ; burner for sounding flame, and set of glass 

 tubes. 



7. For demonstrating the laws of the Vibrations of Bells. 



Bell glass, 8 inches diameter, and squares of blotting paper ; 

 3-inch bell on stand ; 3-inch bell mounted for heating. 



8. For demonstrating the laws of the Vibrations of Plates. 



Set of two glass and two brass plates, 6 inches diameter, 

 with stand and thumbscrew ; box of silver sand. 



9. For demonstrating the laws of Longitudinal Vibrations of Rods. 



Glass tube, J-inch diameter, 3 feet long, sealed at one end ; 

 lycopodium; brass rod, -J-inch diameter, 3 feet long; 

 flannel, leather, and rosin. 



