Intelligence and Miscellaneous Articles. 231 



present prevents the fire from spreading, a drop placed upon a piece 

 of wood leaving after combustion only a charred spot. When not in 

 use, the prisms should be kept in an iron pot with a tight cover. In 

 this manner I have employed and preserved two during a long and 

 hot summer. The viscid or, rather oily nature of the solution serves 

 to prevent, to a great extent, the formation of ascending and 

 descending currents from slight changes of temperature ; and when 

 the prisms are well shaken before use, the definition remains perfect 

 for a long time. In my spectroscope the prisms rest upon a plate of 

 glass instead of upon one of metal. — Silliman's American Journal, 

 July 1870. 



ON THE PROPAGATION OF SOUND IN TUBES. 

 BY M. AD. SEEBECK. 



It is admitted that the velocity of sound propagated in a tube is 

 less than in the open air, and the smaller the tube the less the velo- 

 city*. Kirchhoff has given the following formula for the velocity of 

 sound : — 



V=A 



V 2rV»7r/ 



in which A is the velocity in air, r the radius of the tube, n the num- 

 ber of vibrations, K a constant dependent on the calorific conduc- 

 tivity and on friction. This formula is the same as the one given 

 by Helmholtz, except the meaning of the constant K. 



The method employed by Seebeck does not differ materially from 

 that which Schneebeli adopted in order to verify Helmholtz's for- 

 mula, and of which he has already given an account^. 



The apparatus used was constructed of a horizontal tube, closed near 

 one end by a moveable piston ; near the other a very narrow lateral 

 tube was soldered, to which a caoutchouc tube was fitted which com- 

 municated with the ear. A sound was produced in front of the open- 

 ing of the tube by means of a tuning-fork fixed horizontally to a piece 

 of wood insulated by some caoutchouc supports. That the ear may 

 hear distinctly the sound produced by the tuning-fork, at the junc- 

 tion of the large tube closed by the piston and the small tube com- 

 municating with the ear there must be a node, due to the coexist- 

 ence of direct and reflected waves against the piston. If a loop is 

 produced, the sound perceived by the ear will have its minimum in- 

 tensity ; it is this character which is to be appreciated ; and it is then 

 known whether the distance from the piston to the opening of the 



small tube is equal to -, or in general to (2w+l)-, A being the 



wave-length of the sound produced ; from this we get the velocity 

 of sound by the formula V=«\, n being the number of vibrations of 

 the corresponding sound. The whole section of the tube was agi- 

 tated, which KirchhofF's formula presupposes, except for the largest 



* Annates de Chimie et de Physique, S. 4. vol. xv. pp. 487, 492, 

 "J* Ibid. vol. xvii. p. 512. 



