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PROCEEDINGS OF THE AMERICAN ACADEMY. 



temperature. This method has the advantage of avoiding the use of the 

 air thermometer and of furnaces in which fusion of the metals takes 

 place. The amount of metal which it is necessary to melt is almost 

 infinitesimal. The loops used in each observation weigh only a fraction 

 of a milligram, and the operation may be repeated time after time at the 

 will of the observer with the greatest ease. On the other hand it should 

 be noted that the method is applicable only to such metals as will fuse 

 before oxidation in the hot layers of the acetylene flame. It is not prac- 

 ticable with magnesium, aluminium, zinc, or iron, since these oxidize 

 under the conditions of the experiment instead of fusing. For ouch of 

 the metals of the platinum group as have melting-points below that of the 

 junction itself, and for gold, silver, and copper, the method is a convenient 

 one, and its accuracy is, I believe, fully equal to that of any other method 

 which has thus far been employed. To guard against the deleterious 

 influence upon the thermo-junction of the vapors of the flame, it is impor- 

 tant to bring the latter up gradually by the slow action of the micrometer 

 screw in the manner which I have already described. The atmosphere 

 with which the junction is surrounded under these conditions contains an 



Figure 8. 



