PRACTICAL STANDARDS FOR ELECTRICAL MEASUREMENTS. 



45 



With respect to the measurements of the cross-sections the uniformity 

 of the results show that an accuracy of -001 per cent, may be relied upon. 

 Four methods of measuring the resistance will be employed. At present 

 only two of these are completed. The values in each horizontal line refer 

 to different fillings ; they are quite concordant, as the values given in the 



following table show : — 



Bcsutance in Lahoratory (jY.P.L.) Units of Mercury Tiihes, 



APPENDIX III. 



On the Platinum The^'mometer.i of the British Association, 

 By J. A. Harker, 2>.,yf. 



{From the National Physical Laboratory.) 



The four platinum thermometers numbered BA, to BAj, with which 

 this Appendix chiefly deals, were constructed at the National Physical 

 Laboratory in August 1902. The wii-e used for the ' bulbs ' is approxi- 

 mately 'OOC in. (-15 mm.) diameter, and for the leads ^020 in. (-5 mm.). 



After ascertaining approximately the length of wire necessary to give 

 a fundamental interval of 1 ohm, tiie proper amount for the four 

 thermometers was cut off from the stock reel, and heated in one piece to 

 moderate redness (800° C.) electrically when supported approximately 

 horizontal. The platinum ' lead ' wires, which were of the same quality of 

 purs metal as the finer ' bulb ' wire, were then measured off and the pairs 

 assigned to each thermometer accurately matched. After a preliminary 

 anneal in an oxidising atmosphere at a bright red heat, one of each of 



