PHYSICS. G21 



Da Moncel, in a paper presented to the French Academy, has shown 

 that if one of the poles of a permanent magnet be passed longitudinally 

 along a straight electromagnet, the coil of which is connected to a 

 galvanometer, three induced currents are successively developed ; a 

 first, which results from the approach of the inducing pole, and which 

 is an inverse current; a second, which results from the motion of the 

 magnet from one end of the coil to the other, and which is direct ; and 

 a third, produced by withdrawing the inducing magnet, which is also 

 direct, though the current flows in the same direction as the first, since 

 the magnet acts on the opposite end of the coil. A conclusion drawn 

 from his experiments is that the induced currents due to an approach 

 of the inductor to the polarized core are the same in direction as the 

 currents which produce the magnetization of the latter when the opposed 

 poles at the instant of approach are of the same name. (C. R., Janu- 

 ary, 1883, xcvi, 214.) 



Munro has experimented upon the action of a metal microphone in 

 vacuo, using two square pieces of fine iron-wire gauze — one fixed, the 

 other suspended so as to swing against the other, the whole inclosed 

 in glass. The pressure of the gauze could be regulated by means of an 

 external magnet. The sensitiveness of the instrument was found to be 

 greatly increased when exhausted. (Phil. 2Lag , July, 1883, V, xvi, 23.) 



Several contributions to the theory of the microphone have appeared 

 Bid well thinks the heat at the point of contact plays an important part 

 in the action ; Heaviside finds that the apparent resistance of a con- 

 tact varies inversely as the square root of the current strength, and 

 hence argues against the use of multiple contacts; but their advan- 

 tages in practice have been found very considerable. Munro and War- 

 wick regard the action of the microphone as due to the existence of a 

 silent discharge of electricity through the thin stratum of air at the 

 point of contact ; a view which is sustained by Mr. Stroll's observation 

 that an actual separation of the contact points may be observed in the 

 microscope while the current continues to flow and the instrument to 

 act. Moreover, he has observed that when in action there is a minute 

 repulsion observable between the two carbons, their motion being 

 O.OOOo 1 ™. (Nature, April, 1883, xxvn, 588.) 



On the history of the telephone Thompson has translated some re- 

 markable passages from Philipp Eeis's papers, published in 1860-'t>l. 

 He proposed at that time the name telephone, and sajs the instrument 

 can reproduce to a certain degree the human voice, the consonants be- 

 ing, for the most part tolerably distinct, but the vowels not equally so. 

 One of the forms of his telephone was in the form of the human ear, 

 carved in oak wood, the tympanic membrane and apparatus of trans- 

 mission being made so as to resemble closely the similar parts in the 

 natural organ. (Nature, June, 1883, xxviii, 130.) 



Carhart has observed that an iron plate with a hole in it held in front 

 of the pole of a magnet acts magnetically as a screen just as it would 



