472 Chronicles of Science. [July, 



passed through one of them. By regulating the time between the 

 instant when the wires sound in unison and the instant when they 

 sound again, and noticing the musical interval caused by one of 

 them becoming flat, we have an audible measure of the expansion 

 of the connected wii'e, of the temperature to which it has been 

 raised, and of the quantity of electricity which has traversed it to 

 produce that effect. By continuing the movement, the interval 

 between the notes will increase, and at last the wire operated on will 

 become too slack to sound at all. If coimection with the battery be 

 now broken, and the heated wire be allowed to cool, its note wiU 

 be heard to rise by degrees to its original pitch. With a single pair 

 of plates, the phono-electroscope answers well. The experiment is a 

 striking one in a lecture-room, very instructive, and easily managed. 



According to Bdttger, the metal antimony may replace graphite 

 in galvanic batteries. He finds the following arrangement prefer- 

 able, as regards force and durability, to either Daniell, Minotto, or 

 Leblanche's batteries. A cylinder of amalgamated zinc is placed 

 in a concentrated solution of equal parts of common salt and 

 sulphate of magnesia; the antimony is placed in a porous cell 

 filled with dilute sulphuric acid. 



Mr. Gore, F.E.S., whilst making some experiments on heating 

 strained iron to redness by means of voltaic electricty, observed 

 that, on disconnecting the battery and allowing the wire to cool, 

 during the process of cooling the wu'e suddenly elongated, and 

 then gradually shortened until it became quite cold. The amount 

 of elongation of the wire during the momentary molecular change 

 was usually about 1-240 th part of the length of the heated w4re ; 

 the molecular change evidently includes a diminution of cohesion 

 at a particular temperature during the process of cooling, and it is 

 interesting to notice that at the same temperatm-e during the 

 heating process no such loss of cohesion, nor any increase of 

 cohesion takes place ; a certain temperature and strain are there- 

 fore not alone sufficient to produce it, but the condition of cooling 

 must also be included. 



M. Alvergniat calls attention to the fact, that by simply rubbing 

 one of Geissler's tubes with the di-y hand or a piece of silk, it 

 exhibits the same phenomena of luminosity as if induced by elec- 

 tricity ; the phosphorescence is, however, weak, but may be increased 

 when within the tube substances are deposited which may become 

 phosphorescent under the influence of electricity ; when a tube so 

 arranged is quicldy rubbed, it becomes within a few moments suf- 

 ficiently luminous to serve as a faint hght to see in a dark room. 



