266 
PHYSICS: HULL AND RICE 
measured the effective wave-length of the 'end radiation,' i.e., the short 
wave-length limit of the continuous spectrum, for different voltages up 
to 180,000, and found that this minimum wave-length did not decrease 
continuously with increase of voltage, but approached asymptotically 
a limiting value of 0.172 angstrom units. As will be shown below, 
the wave-lengths found by the spectrometer are much shorter, and 
do not appear to approach any limiting value. 
The spectrum shown in figure 1 was taken in the usual manner with 
a rock salt crystal in continuous slow rotation, photographic plate 
stationary at 19.13 cm. distance from the crystal, collimating slits 
0.2 mm. wide and 20 cm. apart, with a Coolidge tube running at 1 milli- 
WAVE-LENGTHS OF LINES SHOWN IN FIG. I 
L = Designation of line, D = Distance from C in cm., X = Wave-length in angstroms 
L Xo |3i or, 02 a: Ag, 0, m Br 
D 0.964 1.332 1.4Q6 2.614 2.032 2.994 3.332 3 948 4.386 4.494 6.524 
X 0.142 0.196 0.219 0.192 0.215 0.220 0.488 0.192 0.212 0 217 0.463 
L Ag2 k h gdchb'aa' 
D 6.886 7.368 7.604 7.662 7.884 9 074 9.224 9.382 9.558 11.10 11.19 
X 0 487 1.033 1.065 1.073 1.100 1.242 1.260 1.280 1.300 1.468 1.480 
ampere and 100,000 volts constant potential. The horizontal band 
gives the reflection from the cubic (100) planes of the crystal, those 
at 45° from the dodecahedral (110) planes, and those between from the 
tetrahexahedral (210) planes, etc. 
The wave-lengths of the lines and bands in the horizontal strip are 
given in the accompanying table. C, in the photograph, is the un- 
deviated central beam, diminished in intensity by passage through 
a lead strip 2 mm. thick and 5 mm. wide, placed in front of the plate. 
The shadow of this strip extends only one fourth of the distance from 
C to Xo and is not visible on the plate. 
