194 Proceedings of the Royal ^Society of Victoria. 



(2) Specific Resistance. 

 I at first made several determinations of the resistance of 

 the thallium, in the form of short thick wires, and compared 

 its resistance with silvei-, and atterwards with lead, and 

 separately determined the resistances of the specimens used 

 in comparison. I found it much more accurate howevei' 

 to draw the thallium into a finer wire, and determine its 

 resistance directly. This was done with a resistance box, 

 with a shunt on the variable arm. It was measured several 

 times at slightly difl:erent temperatures, as sliown in the 

 following table : — 



t is the temperature centigrade, r and s are the two 

 resistances in parallel which balance the i-esistance of the 

 thallium. R^ is -'^*^, the observed resistance of the thallium, 

 and R is the resistance at 20° C, reduced by the coefiicient 

 •0039 {vid. inf.) The length of the thallium was 4614 cm., 

 and the mean value of diameter measured at different parts 

 along it was '0874 cm., the mean error in measuring it being 

 •0005 cm. The specific resistance at 20° C. is therefore 



TT X ^ 0437^ X -1551 X 10» _ 20170 

 46-14 



(3) Variation of Resistanck with Temperature. 

 To determine this, the thallium was made into a small 

 coil, and immersed in a large beaker of water, with a ther- 

 mometer about the middle of tlie coil. The thallium was 

 connected with the terminals of a slide metre bridge by 

 means of two stout pieces of copper, to which it was firmly 

 bound, and whose resistance was found to be about yAtt of 

 that of the thallium. The resistance of the thallium was 

 balanced with an approximately equal resistance of German 

 silver, which was taken as an arbitrary unit to measure the 

 resistance of the thallium at dift'erent temperatures. By 

 means of a verj'' sensitive galvanometer, the slider could be 

 adjusted to "1 mm., while the whole change in position for 

 a rise of 80° C. was about 70 mm. In reducing the bridge 



