346 E. L. NICHOLS. 



known researclies, I obtaiiied for tlie electromotive forces of my thermo- 

 couple as stated in a previous paragraph. 01S26 volts,, wlieu tlie plati- 

 num side of tlie junctiou was in fusion. Tliis agrées almost exactlj^ witli 

 tlie value obtained b_y extrapolation of a curve plotted from data given 

 by HoLBORN and Wien in tbeir paper. The coïncidence served to esta- 

 blisli at once the identity of the metals used with those emj^loyed by 

 them^ and the delicacy of the method of calibration under considéra- 

 tion. This method bas the advantage of avoiding the use of the air 

 thermometer and of fnrnaces in which the fusion of the metals takes 

 place. The amount of métal which it is necessary to melt is almost infi- 

 nitésimal. The loops used in each observation weigh ouly a fraction of 

 a milligram, and the opération 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 liot outer layers of the acétylène flame. 



It is not applicable to such metals as magnésium, aluminium, zinc, 

 or iron, since thèse oxidize under the conditions of the experiment iu- 

 stead of fusiiig. For such of the metals of the platinum group as hâve 

 a melting-point below that of the junction itself, and for gold, silver 

 and copper, the method is a- convenient one and its accuracy is, I be- 

 lieve, fully equal to that of any other method which has thus far been 

 einployed. As a means of calibrating thermoelements of the kind used 

 in higli température work, its convenience is obvions when we consider 

 that the usual procédure frequently requires months of continued labor, 

 skill of the highest order and extended expérience on the part of the 

 physicist. To guard against the deleterious influence u])on the thermo- 

 junction of the vapors of the flame, it is important to bring the latter 

 up gradually by the slow action of the micrometer screw in the manner 

 which I hâve already described. The atmosphère with which the junction 

 is surrounded under thèse conditions contains an excess of oxygen and 

 even where the métal to be melted is platinum itself, fusion occurs 

 before the lurainous jiortion of the flame, the action of which upon the 

 thermo-electric properties of the junction is to be feared, has been 

 reached. It is well known that a junction, the performance of which 

 has been vitiated by exposure to the vaj^ors of a flame or furnace, can 

 be restored to its original condition by immersion in an oxydiziug flame. 

 In this method of calibration the junction is continually subject to such 

 oxydation as is necessary to préserve it. Thus one of the sources of 



