350 RECORD OF SCIENCE FOR 1886. 



tluced their images on the plate, which was moved by a special mech- 

 auism. (C. K., August, 1880, ciir, 340.) 



Fossati has suggested the use of the microphone, iu order to deter- 

 mine the i)osition of the nodes and loops in a sounding air column. The 

 microphone is connected in the circuit of a telephone and one oi two 

 cells of battery, and is lowered into the vibrating tube. At the nodes 

 it is thrown into vibration and the telephone sounds strongly. If the 

 telephone is omitted and the battery increased to live or six Bunseu 

 cells, then on using a glass tube and lowering the microphone into it iu 

 the dark, bright sparks are observed at the nodes where it is thrown 

 into vibration, while at the loops it remains dark. Tliis form is striking 

 as a lecture experiment. (II Nuovo Cimento xvii, 261 ; J. Phys., De- 

 cember, 1886, II, V, 560.) 



Thompson has expressed the opinion that the fact that the frequency 

 of vibration of an electrically-maintained fork is continually changing, 

 is in consequence of giving the impulses to the prongs at a disadvan- 

 tageous moment, namely, when they are at the extremities of their 

 swings. It is desirable, therefore, that the impulse should be given at 

 the middle of the swing, and to effect this he has suggested that each 

 fork should make and break the circuit of the magnet influencing the 

 other one, and he has shown how the electrical connections can be 

 made to effect this in a simple manner. (Nature, July, 1886, xxxiv, 283; 

 Phil. Mag., August, 1886, V, xxii, 216.) 



C A. Bell has presented a paper to the Eoyal Society upon the sym- 

 pathetic vibration of jets, giving the results of extended experiments 

 upon both gaseous and liquid jets, their vibrations being studied by 

 placing some portion in circuit with a battery and telephone, thus ren- 

 dering these vibrations audible. (Science, June, 1886, vii, 491.) 



Wead has experimented to determine the actual time of contact 

 between the hammer and the string in. a piano. The method was sim- 

 ple. An electric circuit was com[)leted through a cell, a resistance box, 

 a galvanometer, a fine wire round the stem of the hammer, a slip of 

 thin gold foil glued to the face of the hammer, the piano string, and 

 the frame. The contact between the hammer and string produces a 

 momentary closing of the circuit and a throw of the galvanometer needle, 

 from the amount of which the time of closing may be calculated. The 

 observations upon C, which made thirty-four double vibrations per sec- 

 ond, were very satisfactory and showed that the contact time for a very 

 soft stroke is about 20 per cent, greater than for an ordinary or hard blow. 

 The conclusion reached is that for an ordinary blow the time of contact 

 is one-sixth of the vibration period of the string instead of three-four- 

 teenths as was estimated by von Helmholtz. (Am. J. Sci., iJs^ovember, 

 1886, III, xxxii, 366.) 



Violle has described to the French Academy an apparatus for show- 

 ing the two modes in which a vibratory motion is reflected according as 

 the end of the tube is open to the atmosphere or is closed by a solid 



