25 G ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



-which passes by a wire to the other tube, affecting its menis- 

 cus, and causing oscillations in the mercury which reproduce 

 the sound. The return current is through, earth. 



Page has succeeded in demonstrating the currents pro- 

 duced in the telephone, using for the purpose a Lippmann's 

 capillary electrometer. De la Rue has measured the 

 strength of the telephone current, and concludes that it does 

 not equal that which a Daniell's cell would give through a 

 resistance of 100,000,000 ohms. Brough has estimated it, 

 even at a maximum, as only the 1,000,000,000th of a centim- 

 eter-gram-second unit. Breguet has pointed out that the 

 effect of the telephone is much improved by placing one or 

 more vibrating plates (perforated at the centre) at about 

 one millimeter in front of the ordinary plate of the tele- 

 phone. 



Hughes has presented a paper to the Royal Society on an 

 instrument he has devised for magnifying weak sounds, and 

 which he calls a microphone. In its best form it consists of 

 a stick of gas carbon placed vertically, and supported loosely 

 between two small blocks of carbon fastened to a piece of 

 thin board. When an electric current passes through the 

 carbon, an ordinary telephone being in circuit, the slightest 

 jar, and even the vibrations of the voice, is sufficient to in- 

 terrupt the contact at the surfaces. This varying the cur- 

 rent strength causes a sound in the receiver. The sensitive- 

 ness of the instrument is surprising the ticking of a watch, 

 the brush of a camel's-hair pencil, the tread of ally, all being 

 readily audible at the distant telephone. The principle of 

 varying the resistance of a circuit by varying the number of 

 points of contact in it, upon which these phenomena depend, 

 was first utilized by Edison in January, 1877, and has within 

 a year been brought to great perfection in the construction 

 of the carbon telephone transmitter. The disks of carbon, or 

 of silk thoroughly impregnated with carbon, he has also used 

 in his tasimeter, which in various forms serves as a thermom- 

 eter, barometer, hygrometer, and anemometer in a new and 

 simple rheostat, and in a new relay contrived expressly for 

 the relaying of telephone currents. Other workers have also 

 discovered this sensitiveness of contacts. 



