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ANNUAL REPORT SMITHSONIAN INSTITUTION, 1918. 



surface of the wire is brightly polished and remains so for several 

 weeks when exposed to the air. It was wound loosely on a bone 

 core. Connections were made by soft soldering with a miniature 

 copper, using a fusible solder of melting point slightly above 100°. 

 There is some difficulty in making a successful soldered connection 

 because of the low melting point of indium, which is about 155°. 

 It alloys very rapidly with any ordinary solder, forming an alloy 

 of much lower melting point than any of the constituents. It must 

 be caught by the solder with a single well directed touch. 



Successful runs were made at 0°, 25°, and 50°, but at 75° the 

 soldered connections dropped off. Difficulty because of alloying 

 also made it necessary to omit the usual temperature seasoning. 

 This in any event is not so necessary for a low melting metal as 

 for a higher one. 



Without going into the details of Doctor Bridgman's measure- 

 ments, in which he follows the changes of the various phenomena 

 observed as they depend upon pressures and temperatures at differ- 

 ent magnitudes, it may be interesting to the reader to give a brief 

 summary of the behavior of a score of metals with regard to the 

 coefficient of change of resistance for varying temperature and vary- 

 ing pressure. I take this data from Doctor Bridgman's publication 

 without intending to imply that it is altogether new. 



Resistance coefficients. 



