284 Profs. Dewar and Fleming on the Electrical 



The temperatures in the last column in the above Table are 

 platinum temperatures, as given by the thick platinum wire. 

 If the above specific resistances for the thin platinum wire are 

 plotted out in terms of pt, they give a straight line which cuts 

 the axis of temperature at — 272'5^or,ten degrees nearertothe 

 zero Centigrade than in the case of the thick wire. The coeffi- 

 cients of the two wires are slightly different, and the platinum 

 temperatures, as determined by the two wires, are slightly 

 different also, but differ by less than half a degree at the 

 boiling-point of oxygen, and by about one tenth of a degree 

 at the boiling-point of ethylene. When plotted in terms of 

 air-thermometer temperature, the platinum resistance-curves 

 are curves which are concave dowmwards. Hence the co- 

 efficient of resistance- variation with temperature is a variable 

 quantity. The first differential coefficient dR/dt has a posi- 

 tive sign, and the second differential coefficient d 2 R/cft 2 a 

 negative sign. 

 § 8. II. Gold. 



This gold was prepared and drawn into wire for us by 

 Messrs. Johnson and Matthey. It was reported by the 

 assay ers as of 99*9 degrees of fineness. 



Length=100 centim. Mean diameter ='0078653 centira. 



Mean sectional area ='000048586 sq. centim. 



L °^° [^llngth 011 ] = 2 ' 6865 159 = l0gl °^ 



■Rt. 



Corrected 

 resistance 

 in ohms. 



t°. 



Centigrade 

 tempera- 

 ture. 



Pt- 

 Volume- 

 specific 

 resistance. 



pt. 



Platinum 

 tempera- 

 ture. 



Remarks on nature of 

 Bath. 



7-8048 

 6-7068 

 6-0538 

 4-7882 

 4-8319 

 4-7882 

 4-7726 

 4-7636 

 4-7208 

 4-5296 

 3-8056 

 3-1870 

 2-8131 



194-5 

 132-2 

 90-4 

 50-0 

 18-7 

 16-25 

 15-4 

 14-3 

 11-95 

 1-05 



3792-1 

 3258-6 

 2941-3 

 2606-5 

 2347-7 

 2326-4 

 2318-8 

 2314-5 

 2293-7 

 2200-8 

 1849-0 

 1548-5 

 1366-8 



191-5 | 

 131-2 | 



90-55 



506 



19-1 



16-6 



15-7 



14-6 



12-2 

 1-05 



- 44 



- 81-9 

 -106-1 



In melted paraffin. 

 In paraffin oil. 



In melting ice. 



In C0 2 and ether. 

 In liquid ethylene. 

 In liquid oxygen. 



1-4022 





681-3 



-197-1 



= 2197 C.G.S. units. 



Volume-specific resistance at 0° C. 

 Mean temperature-coefficient between 



0°C.andl00°C =-00377 = «. 



