PHYSICS. 281 



himself published the same fact in the Scientific American one or two years 

 before, and had given a figure of several of these chalk cylinders con- 

 nected in series for the purpose of producing a current of high poten- 

 tial.— (^Ya^wre, xxi, 417, March, 1880.) 



Blyth has communicated to the Royal Society of Edinburgh the gen- 

 eral fact that electric currents are produced by the mere friction between 

 conducting substances. Since for all pairs of metals yet tried these 

 currents are in the same direction as the thermo-curreut produced by 

 heating the junction of the same two metals, the author thinks that they 

 may have in part a thermo-electric origin ; but another part may be due 

 to the currents suggested by Sir William Thomson as the cause of fric- 

 tion, and still a thii'd part to the force of contact between films of air or 

 oxide on the surfiices. One of the motors constructed consists of a 

 cylinder of antimony arranged so as to be rapidly rotated, and a plate 

 of bismuth which is pressed hard against it by a spring. When included 

 in the circuit with a microphone and a Bell telephone, the current from 

 it is quite sufficient to serve for the transmission of musical sounds and 

 loud speaking. By using a cylinder of bismuth on which a bent sew- 

 ing needle presses as it rotates, a very good receiver is also produced. 

 The authou ascribes the result to a heat change, analogous somewhat to 

 that observed in the Trevelyan rocker. — {Nature^ xxii, 330, August, 

 1880.) 



Heraud has proposed a new voltaic cell, the negative plate of which 

 is zinc immersed in a concentrated solution of ammonium chloride, while 

 the positive consists of a plate of carbon surrounded by fragments of 

 carbon mixed with about an equal weight of mercurous chloride (calo- 

 mel) in powder. In action the mercurous chloride loses chlorine, and is 

 reduced to metallic mercury ; the zinc acts on the ammonium chloride, 

 producing zinc chloride and ammonia; and the ammonia water and 

 chlorine unite again to reproduce the ammonium chloride. It is claimed 

 that this battery does not polarize, and can be used on a closed circuit. 

 Its electromotive force is not far from that of a Daniell cell. — (Arm. Cliim. 

 Phi/s., V, xvii, 512, August, 1879.) 



Xiaudet has constructed a voltaic cell, the plates of which are also 

 zinc and carbon ; but the former is immersed in a solution of common 

 salt and the carbon in a porous cup containing commercial chloride of 

 lime (a mixture of chloride, oxide, and hypochlorite of calcium). Under 

 the action of the polarizing hydrogen, the hypochlorite is decomposed 

 into hydrochloric acid, which forms calcium chloride with the Lime pres- 

 ent, and vrater ; so that the salts produced by the battery when in action 

 are zinc chloride and calcium chloride. Since both are extremely solu- 

 ble, the liquid preserves its limpidity, and no insoluble salt is formed. 

 The electromotive force of this battery is 1.0 volts. It polarizes only 

 when closed on short circuit, from which it recovers rapidly. Its chief 

 merit is that, like the Leclanch6 cell, the zinc is not acted on until the 

 circuit is closed. To prevent escape of odors, the oi)ening in the porous 

 cell is closed with a waxed cork. — {J. Phys., ix, 18, January, 1880.) 



