﻿250 Dr. J. W. Low on the Velocity of Sound in 



must greatly affect the wave-length and the velocity of sound 

 in narrow tubes. Their theory agrees only imperfectly with 

 the results of Kundt, who employed mixed notes ; with those 

 of Schneebeli, Seebeck, and Kayser, however, all of whom 

 used pure musical tones, the accord is somewhat better. The 

 methods of the last named inquirers, though correct in prin- 

 ciple, are, however, in detail liable to various objections ; I 

 have therefore subjected the whole question of the indirect 

 determination of the velocity of sound to a fresh investigation. 

 The questions I set myself for answer were : — 



1. How does the velocity of sound vary in air and gases for 

 pure notes of different pitch in tubes of different diameter ? 



2. How can the true velocity of sound in unlimited space 

 be determined from that found in tubes ? 



§ 2. Metliod of the Inquiry. 



At the suggestion of Prof. Quincke I measured the wave- 

 lengths for tuning-forks of known vibration-frequency by 

 means of his interference-tubes. I observed, not one minimum 

 of vibration-intensity, as Seebeck had done, but successive 

 maxima, by shortening the tubes by one, two, or more half 

 wave-lengths. My apparatus (fig. 1) consisted of a wide 

 glass tube U, closed at the bottom with a cork and a stop- 

 cock H. From H a long piece of guttapercha tubing led to 

 a water-bottle F ; a second piece of narrower tubing con- 

 nected the side-tube A, distant about 5 centimetres from the 

 upper end of the main tube, with the ear of the observer at C, 

 ending in a glass pipe coated with sealing-wax, so as to fit 

 exactly into the outer passage of the ear. By raising and 

 lowering the bottle F a swimmer B could be brought to any 

 desired point of the interference-tube, and the exact position 

 of its upper smooth surface could be read off on a millimetre- 

 scale fixed behind the tube. The swimmer consisted of a 

 cork 4 centim. long, loaded at the lower end with lead and 

 coated with stiff paper and paraffin. The cork had almost 

 the same diameter as the tube. 



The theory of vibrating air-columns, as developed by 

 Kirchhoff, postulates a regular motion of the air-particles 

 parallel to the axis of the tube. In the course of my experi- 

 ments, however, whether the bare prong or the resonance- 

 box of the tuning-fork was held over the opening of the tube, 

 or the fork-handle pressed firmly against any point of its 

 sides, or the fork, with box attached, removed to any part of 

 the room, I failed to observe any change in the positions of 

 the maxima. These positions could, however, be most easily 



