16 Mr. C. Barus on the Fusion 



Table IV. — Calibration of Platinum-Indium Thermocouples. 



Series V. 



No. 



*20 



T. 



No. 



e 20 



T. 



No. 



C 20 



T. 





microvolt. 



°C. 





microvolt. 



°0. 





microvolt. 



°0. 



38 



5370 



512 



38 



9030 



774 



38 



7580 



671 



38 



5560 



526 



38 



11700 



958 



38 



6860 



622 



' 38 



5900 



565 



38 



11950 



978 



38 



6300 



579 



38 



5930 



568 



38 



12300 



1002 | 



38 



5740 



539 



38 



6030 



560 



38 



12430 



1006 ! 



38 



5290 



501 



38 



6100 



567 



38 



11470 



935 



38 



4880 



467 



38 



8340 



734 



38 



10130 



852 | 



38 



4450 



435 



38 



8500 



742 



38 



9190 



790 



38 



4100 



405 



38 



8850 



760 



38 



8270 



722 









16. Chart. — The results of these three tables are repre- 

 sented graphically by making e 30 a function of T in PI. I., 

 which may be said to be the final result of the calibration 

 problem in hand. Caudal dashes, which point upward and to 

 the right when the furnace temperature is increasing, and 

 downward or to the left when it is decreasing, distinguish the 

 different series of points. It is to be remembered that into 

 this chart are crowded all the accidental errors and observa- 

 tional errors of air-thermometer and thermoelectric measure- 

 ment, when the whole work is done by a single observer. If 

 the curve, PI. L, be linearly prolonged above 1200°, then 

 the junction of the couple eventually fuses at 1800° ; as I find 

 by experiment. 



Discussion. 



17. Errors of Measurement. — To interpret the chart, 

 PL I., it is necessary to enter minutely into a consideration 

 of the observational errors which affect the result 1° in 1000°. 

 The divers quantities which enter saliently into the. equation 

 for constant-pressure air-thermometry are — 



t, T x , ¥,/», v'lv, H/A, «, /3, 



where t is the fiducial temperature and v the volume of the 

 bulb, h the fiducial tension of the gas ; where at the high tem- 

 perature, V 1? T x , H are the volume, temperature, and tension 

 of the gas in the manometer ; and where finally v' y a, /3 are 

 the stem volume and the coefficients of expansion of gas and 

 of porcelain respectively. I have done this both for the 



