SCIENCE- GOSSIP. 



CONTRIBUTED BY W. H. CADMAN. 



Interesting Acoustical Experiment. —An 

 interesting acoustical experiment has been noted 

 recently in the " Physical Eeview." A light hollow 

 cylinder had one end closed by a thin disc, the 

 other end being left open. This cylinder was 

 placed in a stationary sound-wave, with its axis 

 at right angles to the direction in which the wave 

 travels. The source of sound in the experiment 

 was an organ-pipe. It was found that the cylinder 

 moved in the direction of its axis with a certain 

 velocity, and the motion was observed to be inde- 

 pendent of the pitch of the note. A curious result 

 was obtained by fixing four cylinders on a rotating 

 shaft placed with its axis of rotation perpendicular 

 to the wave-fronts. The sound-waves from the 

 organ-pipes then caused the cylinders to revolve 

 in a somewhat similar manner to the cups of an 

 anemometer, except when placed at the nodes. 

 This novel phenomenon is a simple result of 

 Bernouilli's well-known relation between the press- 

 ure ' and velocity in a fluid. The air on the out- 

 side of the cylinder is moved to and fro across the 

 disc by the sound-waves, while the air inside is 

 undisturbed, thus setting up a difference of pressure 

 on the two sides of the disc. 



Phosphorescent Plants. — A species of fungus 

 exhibiting phosphorescence in a very beautiful 

 manner has just been met with in a coal-pit in 

 North Staffordshire. In the dark the timber posts 

 supporting the roof presented a brilliant glow, 

 which was found to be due to a brown-coloured 

 fungus. The power of emitting light in the dark 

 by such plants is a purely physical phenomenon. 

 The phosphorescence has nothing to do with the 

 luminosity of phosphorus, which is due to slow 

 oxidation. The chief point of interest about the 

 above cryptogamous plant is that it continues to 

 shine in the dark for an exceptionally long time 

 after exposure to light. The duration of fluor- 

 escence after the incident light has been cut off is 

 very short in most substances exhibiting phos- 

 phorescence ; often the time is so limited that a 

 special apparatus, such as Becquerel's phosporo- 

 scope, is necessary to detect the existence of 

 phosphorescence. The intensity of the light emitted 

 by the above specimen varied with the temperature, 

 being less in a warm situation than when examined 

 in a cooler place. The light absorbed during ex- 

 posure is emitted as light of lower refrangibility. 

 The best-known phosphorescent fungus is the de- 

 structive parasite and destroyer of timber Agonicus 

 vwllcus, which emits a steady white homogeneous 

 light in the dark. 



Open Currents. — A very delicate experiment 

 has recently been performed by M. V. Cremieu 

 with the object of experimentally realising open 

 currents. The author obtained results showing the 

 non-existence of any magnetic effect from electric 

 convection ; the direct consequence of this result 

 points to the existence of open currents. In the 



experiment an ebonite disc was gilded along radial 

 sectors which were separated from each other. 

 These sectors were then charged by influence with 

 an inductor touching a metallic brush, and they 

 afterwards discharged themselves upon a brush 

 attached to the first by a conducting wire. It was 

 found that the convection of the circuit thus estab- 

 lished did not produce any magnetic effect, whilst 

 the conduction produced it very appreciabl)\ 



A Circular Slide Kule. — The "Journal de 

 Physique : ' contains a description of a simple 

 circular slide rule. This instrument consists of 

 a graduated dial containing two needles. The 

 one needle is pivoted inside the other in such a 

 manner that when the outer one is turned through 

 any number of degrees the inner needle revolves 

 with it. If we want to multiply any two numbers, 

 say x by y, with this rule it is only necessary to 

 place one needle opposite x and the other opposite 

 unity. The needles are then turned together until 

 the one placed opposite unity arrives opposite y. 

 The other needle will now be found to be opposite 

 the reading on the graduated dial corresponding 

 to the product xy. By means of this circular 

 slide rule we can also perform division or find a 

 fourth proportional to three given numbers in a 

 very easy and simple manner. This ingenious 

 slide rule seems likely to be of much practical 

 use. It satisfies three important conditions : it is 

 accurate, easily manipulated, and equivalent to an 

 exceedingly long rule in a small compass. 



Singing and Sensitive Flames. — The musical 

 sounds produced by flames are allied to sounds 

 produced by organ-pipes ; the flame, instead of 

 the air-blast, being the cause of the vibration of 

 the column of air enclosed in the pipe. Such a 

 sound is produced by the flame of the fire at the 

 bottom of a chimney ; but since the vibrations of 

 the long air-column enclosed in the chimney are 

 very slow, the sound is extremely low, and can 

 scarcely be called a musical note at all By 

 enclosing gas flames in metal pipes of proper 

 dimensions it is possible to get musical notes 

 quite equal in quality to those of an organ. As 

 the length of the pipe and its air-column is 

 lessened, we pass from low to high notes, owing to 

 the vibrations following one another more rapidly. 

 The sound is doubtless produced by the fluttering 

 of the flame caused by the rapid current of air 

 passing over it. It is easy to show that the flame 

 really does nicker whilst it is singing, by getting 

 the image of the flame reflected from a small 

 mirror and then rapidly revolving the mirror on 

 its axis. A continuous band of light is obtained 

 as the image of a silent tlame ; but with a singing- 

 flame the band is broken up considerably, showing 

 that whilst singing the flame is dancing rapidly 

 up and down. The pitch of the note is mainly 

 influenced by the size of the flame and length of 

 the tube, also by the position of the flame in the 

 tube. Some tubes may be silent to all but one 

 note. Silent flames enclosed in tubes are very 

 sensitive to sound. Each flame is found to be 

 sensitive to special sounds only, the vibrations of 

 such sounds being suited to produce sympathetic 

 vibrations in the gas which feeds the flames. By 

 arranging the gas pressure so that the flame of a 

 burner is on the verge of flaring, the flame sinks 

 and jumps to each note of appropriate pitch, a 

 whistle or shake of a bunch of keys being often 

 sufficient for the purpose. 



