PHYSICS. 479 



tact, though iiisuhitetl from each other, as a coutinuousflat layer about 

 16 inches h)iig-, soldered end to end in an alternating- series. About 1 J 

 inch in length at each end is bent downward so as to dip into two 

 liquids of different temi)erature8 contained in two long, narrow troughs. 

 The hot one is melted paraffin, kept at 120°; the cold one is a non-vola- 

 tile petroleum. The resistance of 295 pairs of such wires was 05.0 ohms 

 at 10° C; and when the difference of temperature in this two baths was 

 100° the electro- motive force was 0.7729 volt, and when it was 130°, 

 1.005 volts. Each element gave, therefore, 0.00002G2 volt tor 1°. With 

 this apparatus measurements have been made to the 33-5-00 part of a 

 volt. The author finds it very useful in practice. {Nature, March. 

 1884,. XXIX, 513.) 



Von Walteuhofeu has observed that the Noe thermo-battery is capa- 

 ble of taking a charge like an accumulator. When the current of a 

 battery is sent for a few moments through one of these generators, it is 

 capable of yielding a counter-current, due, of course, to the well-known 

 Peltier effect. A different effect, however, was observed according to 

 the direction of the charging current. When this current was in one 

 direction, the discharge currents were proportional to these and were 

 always in. the opposite direction. But when the charging current w^as 

 rcA'ersed, the discharge current at first increased to a maximum, then 

 decreased to zero, theu began in the reverse direction, or that of the 

 charging current. The author ascribes this anomalous result to the 

 unequal heating of the junctions. {Nature, January, 1884, xxix, 227.) 



Two important papers have api>eared having for their object the dis- 

 cussion of the theory of the dynamo-electric machine. The first of these 

 is by Clausius ( TF^erf. Ann., xx, 353; Phil. Mag., January, February, 

 1884, V, XVII, 40, 119,- J. FlujH., July, 1884, II, ill, 313), and the other, 

 on machines with alternating currents, by Lucas (0. i?., March, 1884, 

 xcviii, 070), who used the Meritens machine in his experiments. 



Fitzgerald has sought to produce a non-sparking dynamo by apj)ly- 

 ing the principles of Maxwell's modification of Thomson's electric doub- 

 ler to a dynamo, in which the current passes through two or more coils 

 in parallel circuit. Under these circumstances it is possible to arrange 

 the magnetic field and the brushes so that when the terminals of any coil 

 come into contact with their brushes the terminals shall be at the same 

 difference of potential as the brushes, so that when they break contact 

 there shall be no current circulating in the coil, and therefore no sparks 

 produced. The energy of self-induction, usually wasted on local cur- 

 rents and sparks will now be spent in the production of useful current, 

 {Nature, July, 1884, xxx, 331.) 



3. Electrical Units and Measurements. 



The International Electrical Conference held in Paris in April con- 

 cluded the business befoi'e it and adjourned finally. Each section 

 ado])ted resolutions as follows : First section, electric units : (1) The 



