90 Mr» Moyle on Granite Veins, [Aug. 



separately heard, or they may botli be heard in combination by 

 connecting both the conductors with sounding boards. 



The phenomena of diffraction regarding only the form of the 

 surfaces, or the superficies over which the vibrations extend, are 

 by the conformation of the organs of hearing, not of any conse- 

 quence to the perception of sound, though the same phenomena 

 when the chromatic vibrations are concerned, are very evident 

 to the eye. They, however, undoubtedly take place equally in 

 both instances, and may be well explained by the theory already 

 laid down. Each separate vibration propagating itself in the 

 plane of its vibrating axis, a number of vibrations in different 

 planes, after passing through an aperture, naturally expand 

 themselves transversely as well as rectilineally, and thereby 

 occupy a greater space than they would, were they only longitu- 

 dinally transmitted. 



I have still to indicate a new property of the phonic vibra- 

 tions, but whether it is analogous to any of the observed pheno- 

 mena of light, 1 am yet ignorant. When the source of the 

 vibrations is in progressive motion, the vibrations emanating 

 from it are transmitted, when the conductor is rectilineal and 

 parallel with the original direction, and they are destroyed when 

 the conductor is perpendicular to the direction, though the axis 

 of vibration and the conductor, being in both instances in the 

 same place, would transmit the vibrations were the phonic sta- 

 tionary. These circumstances are proved by the following expe- 

 riments : When a tuning fork placed perpendicularly to a rod, 

 communicating at one or both extremities with sounding boards, 

 and caused to oscillate with its vibrating axis parallel with the 

 rod, moves along the rod, preserving at the same time its perpen- 

 dicularity and parallelism, the vibrations will not be transmitted 

 while the movement continues, but the transmission will take 

 place immediately after it has remained motionless. When the 

 tuning fork moves on the upper edge of a plane perpendicular to 

 a sounding board, the vibrations rectilineally transmitted will 

 not be influenced by the progressive motion. 



Article II. 

 On Granite Veins, By M. P. Moyle, Esq. 

 (To the Editor of the Anflals of Philosophy.) 

 DEAR SIR, Hektotiy May 7, 1823. 



Various statements and representations, have from time to 

 time been given, of the gigantic granite veins which are so very 

 conspicuous in the slate cliffs about a quarter of a mile east of 



