304 Profs. Dewar and Fleming on the Variation 



in liquid or in solid air, or at any other temperature up to 

 + 100° C. 



Amongst other specimens a wire was pressed from some 

 commercial bismuth, supposed to be fairly pure, which 

 will be distinguished by being called Griffin's Bismuth ; the 

 diameter of this last wire was about '066 centimetre. The 

 diameters of these wires were carefully measured with a 

 microscope-micrometer in about twenty different places, the 

 lengths of the wires used being about 30 or 60 centimetres. 

 The sample of pure bismuth prepared for us by Mr. George 

 Matthey will be distinguished by speaking of it as Matthey's 

 bismuth, the thicker of the two wires being called A and the 

 thinner B. The dimensions and mean diameters of the 

 pressed wires, which were used just as they came from the 



press, were as follows : — 



Length. Mean diameter. 

 Sample. centim. centim. 



Matthey's Bismuth (Pure), A ... 61*25 0-06713 



Matthey's Bismuth (Pure), B ... 32*70 0*04926 



Griffin's Bismuth 52*90 0*06625 



In addition to these samples of pressed wires, other speci- 

 mens were prepared by drawing melted bismuth up into 

 fine glass tubes and making a suitable connexion with the 

 bismuth for the purpose of an electrical resistance measure- 

 ment by means of tinned copper wires melted in to the ends 

 of the bismuth specimen. These samples of bismuth then had 

 their electrical resistance measured with a Wheatstone bridge 

 in the usual way, the temperature of the specimen being 

 taken at the same time by means of a platinum thermometer, 

 consisting of a platinum wire closely in contact with the 

 specimen of bismuth. All the temperatures which are given 

 in the following paragraphs have been converted into platinum 

 temperatures, taken in terms of our standard platinum ther- 

 mometer Pj, the electrical constants of which were given 

 by us in the paper on the Thermo-electric powers of metals 

 (see Phil. Mag. July 1895). Temperatures so measured are 

 distinguished by the letter P x placed after the number de- 

 noting the temperature. The electrical resistance of the 

 bismuth specimens, all proper corrections being made for the 

 resistance of the connecting wires, was taken at a large 

 number of temperatures lying between the boiling-point of 

 water (100° C.) down to the temperature of solid air, which, 

 in terms of our standard platinum thermometer Pj is about 

 — 233° P x to —235° Pj. From the known dimensions of the 

 bismuth wires the volume specific resistance of the metal was 

 calculated at these different temperatures, and the reduced 

 observations for the three specimens above mentioned are 

 given in the following tables : — 



