88 Mr. Wheat stone on Sound. [Aug. 



cularly on the side of a rectilinear rod; the vibmtions were, 

 therefore, communicated at right angles ; when the axis of the 

 oscillations of the fork coincided with the rod, the intensity of 

 the transmitted vibrations was nt its maximum ; in proportion as 

 the axis deviated from parallelium, the intensity of the trans- 

 mitted vibrations diminished ; and, lastly, when it became per- 

 pendicular, the intensity was at its minimum. In the second 

 quadrant, the order of the phenomena was inverted as in the 

 former experiment, and a second maximum of intensity took 

 place when the axis of the oscillations had described a semi- 

 circumference, and had again become parallel, but in an oppo- 

 site direction. When the revolution was continued, the inten- 

 sity of the transmitted vibrations was varied in a similar manner, 

 it progressively diminished as the axis of the oscillations deviated 

 from being parallel with the rod, became the least possible when 

 it arrived at the perpendicular, and again augmented until it 

 remained at its first maximum, which completed its entire revo- 

 lution. 



The phenomena of polarization may be observed in many 

 corded instruments : the cords of the harp are attached at one 

 extremity to a conductor which has the same direction as the 

 sounding board ; if any cord be altered from its quiescent posi- 

 tion, so that its axis of oscillation shall be parallel with the 

 bridge, or conductor, its tone will be full ; but if the oscillations 

 be excited so that their axis shall be at right angles with the 

 conductor, its tone will be feeble. By tuning two adjacent 

 strings of the harp-unisons with each other, the differences of 

 force will be sensible to the eye in the oscillations of the reci- 

 procating string according to the direction in which the other is 

 excited. 



It now remains to explain the nature of the vibrations which 

 produce the phenomena, the existence of which has been proved 

 by the preceding experiments. The vibrations generally assume 

 the same direction as the oscillations which induce them ; in a 

 longitudinal phonic the vibrations are parallel to its axis ; in a ^ 

 transversal phonic, they are perpendicular to this direction; a' 

 circular or an elliptic form can be also given to the vibrations by 

 causing the oscillations to assume the same forms. Any vibrat- 

 ing corpuscle can induce isochronous vibrations of similar conti- 

 guous corpuscles in the same plane either parallel with, or 

 perpendicular to, the direction of the original vibrations, and the 

 polarization of the vibrations consists in the similarity of their 

 directions, by which they propagate themselves equally in the 

 same plane; therefore the vibrations being transmitted through 

 linear conductors, it is the plane in which the vibrations are 

 made that determines their transmission, or non-transmission, 

 when the direction is altered. A longitudinal or a transversal 

 vibration may be transmitted two ways to a conductor bent at 

 right angles ; their axis may be in that direction, as to be in the 



