ON A QUARTZ THREAD GRAVITY BALANCE. 



229 



Resistance Sox. 



The resistance standards are made of manganin wire according to ST. LINDECK'S 

 indications.* After the box had been in use for a year it was recalibrated and found 

 to have changed slightly, sufficiently to affect estimates of temperature supposed 

 accurate to '002 centim. degrees. The arrangement will be seen from the diagram 

 (fig. 2). We have five coils each of one "box unit," in our case 0*1166725 "legal 



Fig. 2. 



Connections of Resistance Box. 



A. The point of junction of the two equal arms P anil Q. 



B. The contact of the galvanometer connection to the bridge wire. 



C. The junction of the resistance, Q, to the flexible lead of the thermometer. 



D. The junction of the resistance, P, to the flexible " dummy " lead for compensating the resist- 



ance of the thermometer leads. 



E. The connection of the/' hort flexible lead to one end of the variable resistance. 



F. The connection of ' j other short flexible lead to the other end of the variable resistance. 



G. The galranomet 

 K. The battery key. 



M. One end of the coil balancing the thermometer resistance at 5" C. 



N. The other end of the coil. 



P. One of the equal arms. 



Q. The other equal arm. 



R. The platinum wire resistance, constituting the thermometer. 



T. The junction of one of the flexible leads of the thermometer and the divided bridge wire. 



U. The end of the loop of the " dummy " lead. 



V. Junction of the " dummy " lead and the short flexible lead. 



Z. The lottery. 



ohm." We have also five coils five times as great, i.e., equal to five lx>x units of 

 resistance each. The box unit is a resistance equal to the one-hundredth of the 

 change of resistance of the platinum thermometer, when its temperature is changed 

 from C. to 100 C. The manganin bridge wire lies over a glass scale of equal parts 

 which is graduated over a length corresponding to a resistance of one box unit. This 



* 'B. A. Reports,' 1892, p. 139. 



