PHYSICS. 249 



niembrano is in contact on both sides with the air in the pipe, and it 

 vibrates at the looi^s and ceases at the nodes. Bnt if the second end 

 of the tube carrying" the membrane be closed with a cork, the meiidjrane 

 is now in contact only on one side with the air in the pipe, and it vibrates 

 strongly at the nodes and ceases to vibrate at the loops. Seebeck ex- 

 plained this by showing that one of the waves was obliged to go round 

 the tube to reach the membrane, and thus its velocity (^hanged sign. 

 Bichat, in noticing this paper, gives the method he has used for show- 

 ing this result in class instruction. He uses the ordinary closed organ- 

 pil^e with a glass side, made by Koenig. On urging the blast a sound 

 is obtained having a node at about one-third of its length from the 

 mouth and a loop at one-third from the closed end. A membrane of 

 gold-beater's skin, attached to a rigid ring, is first passed through the 

 tube to show in the usual way that the sand placed upon it is disturbed 

 at the loops and not at the nodes. Then a small manometric capsule is 

 used in place of the membrane, having two small glass tubes i^assing 

 from its top through the cover of the pipe. Through one of these coal 

 gas enters, and at the outer end of the other it is burned. On examin- 

 ing this flame in a revolving mirror it will be seen to be in vibration 

 when the capsule is at the node, and at rest when at a loop. — {Ann. Phys. 

 Chem., II, viii, 384; J. Fhys., ix, 102, 1880.) 



Mayer has applied the principle of exploring the wave-surface in air 

 from a sounding body, which he devised some years ago, to the construc- 

 tion of a simple and eflicient apparatus called a topophoue, by which even 

 the unpracticed ear may determine accurately the direction of a distant 

 sound, even in foggy weather. It consists of a vertical rod passing 

 through the roof of the deck-cabin of a vessel, for example, approaching 

 the coast, bearing upon its ui^per en<l a horizontal bar carrying two adjust- 

 able resonators below which is a pointer set at right angles with the bar. 

 Eubber tubes from the resonators pass through the roof of the cabin and 

 unite in a single pipe connected with a pair of ear-tubes. The vertical 

 rod is turned in any direction by means of a handle. The resonators are 

 first accurately tuned to the sound under observation. They are then 

 fixed at a distance from each other somewhat less than the wavelength 

 for this sound, and brought by turning the handle simultaneously on the 

 wave-surface. As they now receive the sound-wave upon their mouths 

 at the same instant in the same jjhase, the ear will hear the sound re-en- 

 forced if the connecting tubes are of the same length, and diminished if 

 one is a half wave-length shorter than the other. When this is attained 

 the bar is a chord in the spherical wave-surface of which the sounding 

 body, say a fog-horn, is the center. Hence the pointer which is perpen- 

 dicular to this bar points out the bearing of the fog-horn with great 

 accuracy. By making a second observation at a known distance and 

 direction from the first, a second radius line is obtained, and the distance 

 of the fog-horn is computed. — {Nature, xxi, 385, February, 1880.) 



Schellbach and Boehm have proposed a simple experiment for show- 



