Intelligence and Miscellaneous Articles. 79 



resistance a, and by means of the divided rule it may be measured 

 almost to the tenth of a millimetre. The compensator serves to 

 determine the value of the ratio k. This apparatus consists of two 

 identical'series of bobbins formed of german silver wire of 0*17 millim. 

 in diameter, and offering great resistance. Each series consists of 

 nine bobbins ; the first constitutes the resistance R ; and by the rest, 

 to a greater or less extent, &R may be constituted, and any values 

 given to k from 1 to 50. A Ruhmkorff's galvanometer with a long 

 wire was placed at about 2 metres distance from the rheostat, and 

 was observed by means of a horizontal telescope and a reflecting 

 prism. By means of a key the current could be instantaneously closed. 

 By means of insulated wire, the rheostat, the compensator, and the 

 galvanometer could be connected either with each other, or with a 

 battery consisting of 2 or 3 Bunsen's cells (which was placed under a 

 shed), or, finally, with the resistance to be measured, which was placed 

 in a furnace-room. To hold the melted metals, I used Bayeux por- 

 celain U-tubes from Mr. Gosse's manufactory. These tubes are 25 

 centimetres in length by 5 millimetres internal diameter ; their two 

 parallel legs terminate in cylindrical cups 2 centimetres in diameter 

 and 4 in height. To effect the fusion of the metals and retain them 

 at a constant known temperature, I used vapour baths such as were 

 employed by MM. Ste.-Claire Deville and Troost in their researches on 

 the density of vapours ; the tube was suspended in the interior of 

 the vessel in which the distillation took place. Boiling mercury, 

 sulphur, and cadmium were used — that is to say, temperatures of 358, 

 440 and 860 degrees. 



Conductibility of a melted metal. — At first the resistance of a tube 

 full of mercury was measured ; then, this tube being arranged in the 

 retort and filled with metal, the resistance was measured during the 

 distillation of the substance employed. This resistance remained con- 

 stant in the vapour of mercury, and also, though to a less extent, in 

 that of cadmium ; but the density of sulphur is too small to maintain a 

 constant temperature in a metallic mass, and the results thus ob- 

 tained leave much uncertainty as far as temperature is concerned. 

 A determination is obtained from the mean of two observations, 

 differing from one another by the relative positions of the two series 

 of bobbins of the compensator. 



Change of resistance in the passage from the solid to the liquid state. 

 — The metallic column was allowed to cool and a series of observa- 

 tions made noting the corresponding times. Curves were thus ob- 

 tained whose ordinates were the resistance and whose abscissas the 

 time, and on which the passage from one state to the other is an 

 almost vertical branch. The results deduced from these curves, 

 taking the two points where the curvature changes to determine the 

 resistances at the point of fusion, may be considered, in consequence 

 of the magnitude of the variation, as being the approximate measure. 



The metals are — tin (stannic acid reduced by charcoal), lead (ace- 

 tate of lead calcined), bismuth (subnitrate of bismuth reduced by 

 charcoal), cadmium (distilled cadmium), zinc (distilled zinc), and anti- 

 mony (tartarized antimony calcined with nitre) . The mercury used 

 had stood for some time under sulphuric acid. The conductivities 

 refer to pure mercury at 21 degrees. 



