1869.] Physics. 151 



metals, resisting tlie highest temperatures, and then to estahhsh a 

 graduated table. As to the practical introduction of the pyro- 

 electric couple, it is easily made. A table of sines has been specially 

 constructed for these observations. 



Electricity. — A new arrangement for furnishing currents of 

 electricity has been made known by M. Ney. It is composed as 

 follows : — 1. A vessel filled with solution of chloride of ammonium, 

 containing a plate of amalgamated zinc. 2. A porous cylinder 

 filled with carbonate of copper, into which a plate of copper 

 plunges. To maintain the battery in action, it is only necessary 

 to add solid chloride of ammonium from time to time. In military 

 telegraphy, where the pile should be capable of transport, the outer 

 vessel might be filled with sand saturated with a solution of chloride 

 of ammonium in the place of the solution. This arrangement 

 recommends itself on the score of cheapness, for native carbonate 

 of cop2Der answers sufiiciently well, and it likewise only requires 

 attention while in actual use. Carbonate of cojjper is insoluble in 

 a solution of chloride of ammonium, but upon closing the current, 

 the chloride is decomposed into hydrochloric acid and ammonia ; 

 the hydrochloric acid collects at the zinc pole, the ammonia at the 

 copper. The carbonate of copper becomes soluble, and its reduc- 

 tion gives rise to a secondary current having the power of a Daniells 

 clement. This form of battery is perfectly constant. 



At a meeting of the French Academy some time ago, M. Sidot 

 showed several samples of iron pyrites possessing magnetic j^olarity, 

 obtained by passing a current of hydrosulphuric acid over the mag- 

 netic oxide. At that time he stated that the direction of the polar 

 axis appeared to be in relation to the position of matters at the 

 moment of their formation with reference to the magnetic axis of 

 the globe. M. Sidot has now tested his supposition further by 

 examining the behaviour of the magnetic oxide of iron, to ascertain 

 whether it suffered the same physical modifications, when placed in 

 the same conditions, as magnetic pyrites, and whether the polarity 

 was produced by the earth by removing all causes foreign to terres- 

 trial action. When a tube of refractory clay is placed parallel to 

 the magnetic needle, in a furnace free from iron, and in the tube a 

 platinum boat filled with colcothar, which is heated to bright 

 redness in a current of air for an hour, the result, after cooling, is a 

 strongly agglomerated grey oxide, possessed of magnetic j^olarity. 

 The extremity of the oxide turned towards the north is a south 

 pole ; it energetically repulses the pole of a magnetic needle j)ointing 

 to the north of the earth. A magnetic oxide is likewise obtained by 

 calcining colcothar in a platinum crucible. The upper extremity 

 of the mass presents a pole opposed to the south pole of the globe, 

 and the lower extremity an opposite pole. To obtain masses pos- 

 sessed of greater magnetic polarity a different disposition was made. 



