CHEMISTRY: HARKINS AND ARONBERG 
713 
then the two lamps were interchanged and six more exposures were 
made, when the positions were again reversed and three more measure- 
ments were made. On the average the wave length of the uranio-lead 
was 0.0043 A. U. longer than that of the ordinary lead. The seventeen 
measurements were as follows, where all should have the positive sign: 
0.0046, 0.0046, 0.0068, 0.0036, 0.0057, 0.0043, 0.0036, (shift of lamps) 
I — 1 -< Qiortz Plote 
FIG. 1 
0.0036, 0.0036, 0.0039, 0.0046, 0.0057, 0.0036, (shift) 0.0046, 0.0036, 
0.0046 A. U. The average difference was 0.012 mm. on the plates, and 
the dispersion was 0.359 A. U. per millimeter. In experiments 6 and 7 
the voltage of the ordinary lead was lowered, and in 12 and 13 that of 
the uranio-lead was lowered, in each case by 3 volts. In experiment 
17 the amperage of the uranio-lead was lowered by 0.2 amperes. It 
