412 Blending of the Sensations of Interrupted Tones. 



flask A ; which is a common form of flask, used by chemists. 

 When the tube T is closed the air in the flask resounds 

 powerfully to the sound of an UT 3 fork, F ; but when this 

 tube is open, the resonator resounds so feebly as to be just 

 audible at the distance of several feet from the flask. 



If the tube be closed and opened several times in a second, 

 we shall have loud explosions with faint interposed sounds. 

 The opening and closing of the tube is effected by a per- 

 forated disk, D, revolving on a rotator, R. The tube T is 

 placed in the circular path of the 16 holes which perforate 

 the disk, with the mouth of the tube quite close to the surface 

 of the disk. A short tube B, with flanges on it, slides neatly 

 over the tube T, and the flange of B is pressed against the 

 surface of the disk D by the helical spring S. By this 

 arrangement the tube T is fully opened when a hole in the 

 disk coincides with the opening of the tube, and is entirely 

 closed when the flange of B is between the holes in the disk 

 and gently pressing against its surface. 



On slowly rotating the disk, while the fork is kept in 

 vibration by an electromagnet, we have the perception of 

 powerful beats which become more and more frequent as the 

 velocity of rotation of the disk is increased till, with a certain 

 velocity, the beats blend into a smooth continuous sound, 

 which is that given by the fork when held near its proper 

 resonator. This sound of UT 3 as given by the blending of 

 its interrupted sounds is, however, accompanied by another 

 and graver sound ; but the existence of this additional sound 

 does not interfere with the clear perception of the blending 

 of the interrupted sounds of UT 3 . With this apparatus the 

 blending of interrupted sounds has been shown to the entire 

 satisfaction of a large audience. 



To enable one readily to make the apparatus, the following 

 dimensions are given. The diameter of opening of mouth of 

 flask is 3 centim. Depth of flask, 16*25 centim. Capacity of 

 flask, including tube T, 483 cubic centim. 



In the figure the rotator, R, is shown driven by a cord. It 

 is necessary, if an accurate determination is to be made of the 

 duration of the residual sensation, to drive the disk by gearing 

 as is done in the apparatus I have used. When the disk is 

 driven by a cord one can show the blending of the interrupted 

 sounds, but an accurate determination of the duration of the 

 residual sensation is prevented by the friction which exists 

 between the flange of B and the disk, though these surfaces 

 are coated with a film of oil. 



