OF ARTS AND SCIENCES : OCTOBER 8, 1867. 415 



into intimate neighborhood, will move so that the vibrations of the air 

 cross one another and produce silence, as Savart showed experi- 

 mentally in the case of pendulums of equal length vibrating in com- 

 pany. 



This peculiar case of unison-pipes I have made a subject of special 

 investigation. In complex cases, it would doubtless be impossible so 

 to arrange the voices and instruments that the total volume of sound 

 should be multiplied in the same ratio as the number of performers. 

 The effect of a large chorus or a large orchestra will disappoint expec- 

 tation, from the unavoidable interferences of sound-waves. But, in 

 the simple case of two unison-pipes, can they be prevented from 

 silencing each other ? The remedy for the evil would be : First, — 

 To sacrifice in a measure the perfection of the unison ; or, Second, — 

 To place them at a distance beyond each other's influence ; or. Third, 

 — To separate them by one half of the wave-length which propagates 

 a sound of the given pitch, or by some odd multiple of that quantity. 

 The latter remedy would answer for auditors in the direction of the 

 line which united the two pipes, though not for the audience generally. 

 In studying the effect of position, I have made the following experi- 

 ments, the ear being the judge ; or the eye, looking at the broken 

 ribbon of light in the revolving mirror. 

 I. The pipes are placed side by side. 



1. With similar ends together, they silence each other. 



2. With dissimilar ends together, they silence each other. 



II. The pipes are placed with their axes upon the same straight 

 line. 



1. If similar ends are together, whichever of the two ends 



be selected, they silence one another. 



2. If dissimilar ends are together, they silence each other. 



III. The pipes are placed at right angles to one another, with one 

 extremity of each pipe at the angle. 



1. If the ends that are played are at the angle, the pipes 



re-enforce each other. 



2. If the other ends are at the angle, they tend to silence 



each other. 



3. If dissimilar ends are at the angle, they re-enforce each 



other. 



