130 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



different places by the same machine. These experiments 

 were made with a view to utilize these lights at the Paris 

 Exhibition. 



Tyndall, in connection with Douglass, has made a report 

 to Trinity House on the comparative value of various mag- 

 neto-electric machines for light-house purposes, an abstract 

 of which appears in Nature for October 25th. The machines 

 compared were those of Holmes, Gramme, and Siemens. 

 The performance of the small Siemens machine particularly 

 impressed them. Its power, in relation to its size, is sur- 

 prising. The large machine of Siemens, however, greatly 

 transcends both his small machine and the single machine of 

 Gramme ; it is sensibly equal to the two Gramme's machines 

 coupled together, the price of the former being less than half 

 that of the latter. The light from the large Siemens, as also 

 that from the two coupled Grammes, is of extraordinary 

 splendor. Combining either the large machine of Siemens, 

 the two Gramme's machines, or, if practicable, the two small 

 machines of Siemens, with one of the group-flashing dioptric 

 apparatuses which have been recently devised by Dr. Hop- 

 kinson, a light transcending all other lights now existing 

 would probably be obtained. 



7. Thermo -Electricity. 



Streintz has described a new form of Noe's thermo bat- 

 tery, and has given the results of some measurements with 

 it. The positive metal consists of an alloy of 62.5 antimony 

 and 36.5 zinc, and the negative metal of German-silver wire. 

 The battery contained four series of 27 elements each, so ar- 

 ranged as to be combined in two series or in one only. The 

 electro-motive force estimated by Fechner's method was that 

 of 4.3 Daniell cells; the resistance, 2.7 Siemens units. 



Naccari and Bellati have investigated the thermo-electric 

 properties of potassium and of sodium at various tempera- 

 tures, using pairs formed by one of these metals and copper 

 in the earlier experiments, and lead in the later. The results 

 show that the passage of a unit of electricity from a cold 

 section to another warmer by one degree, transports, follow- 

 ing the direction of propagation of the negative fluid, a quan- 

 tity of heat equivalent respectively to 2529 units of work for 

 the potassium and 4129 units for the sodium. The neutral 

 points are at 62.04 and 212.4. 



