282 PHYSICS. 



Niaudet has given an illustrated description of the Noe thermopiles 

 constructed by Hauck, of Vienna, and exhibited in Paris. The elements 

 used are German silver, emi)loyed in the form of wire, four from each 

 junction, and an antimony all 03' cast in a mould. Each j)air has an 

 electromotive force equal to 0.1 Daniell cell, for a temperature at which 

 the ends are below redness. It resistance is 0.1 of a Siemens unit per 

 element.— (.7. Pliys., viii, 230, July, 1879.) 



D'Arsonval has suggested an improvement in Plante's secondary 

 batteries, which, as is well known, consist of two sheets of lead im- 

 mersed in dilute sulphuric acid. The action is limited at the cathode 

 ^^Y the hydrogen bubbles which form there, and at the anode by the 

 low conductivity of the lead i^eroxide film which forms over its surface. 

 The first of these difiiculties d'Arsonval obviates by electrolyzing a 

 salt of zinc instead of a dilute acid. The second he avoids by increas- 

 ing the surface of the anode, employing for this purj)ose shot heaped 

 about a carbon plate. The liquid employed is a strong solution of zinc 

 sulijhate. While charging, zinc is deposited ui)on the surface of a lead 

 l^late, or, better, upon a free surface of mercury amalgam, sulphuric acid 

 being produced at the same tiim^ Its electromotive force is claimed to 

 be 2.1 volts. — [Nature^ xxi, 409, February, 1880.) 



Breguet has published a memoir upon the theorj' of the Gramme 

 machine, and on the cause of the dissymetric position of its brushes. 

 The following are his conclusions : 1st. The theory of the Gramme and 

 von Alteneck machines is directly connected with that of Barlow's wheel 

 and Faraday's machine, and these latter machines rest on the first 

 principle established by Ampere, i. e., a movable current tends to place 

 itself in such a position that the observer who personifies it sees the 

 south pole on his left and the north i)ole on his right hand. 2d. The 

 soft iron armature of the von Alteneck machine serves only to re- en- 

 force the magnetic field in the region where the wires of the movable 

 circuit revolve. 3d. The annular armature of soft iron of the Gramme 

 machine has the same influence as the preceding armature, but this is 

 not its characteristic function. This function consists in shielding the 

 internal wires of the bobbin sjjires from the normal action of the lines 

 of force of the field. 4th. The angular displacement of the brushes of 

 the i)receding machines cannot be attributed to the retardation of the de- 

 magnetization of the soft iron ring alone, since this displacement stiU 

 exists and may even become still more considerable in those forms de- 

 rived from these machines where there is no soft iron armature. — {Ann. 

 Chim. Phys., Y, xvi, 5, January, 1879.) 



3. Electrical measurements. 



PeUat has devised a method for measuring electromotive force which 

 may be applied to a battery or may be used to determine the difference 

 of potential between two metals in contact. The principle consists in 

 opposing to the cell to be measured an electromotive force variable at 



