PHYSICS: HULL AND RICE 
267 
The short wave-length Hmit of the spectrum, marked Xo, is the short- 
est wave-length that is produced by electrons of velocity corresponding 
to the operating voltage ^^100,000) and its value, 0.142 angstrom units, 
agrees very closely with the value given by Duane and Hunt's for- 
mula, eV =hv,nax= he /Xn^in- I have already shown^ that the proportion- 
ahty between frequency and voltage holds accurately up to 100,000 
volts, and these measurements have since been extended, with less 
accuracy, up to 150,000 volts. The shortest wave-length so far ob- 
served is 8x10-10 cm., or 0.08 A.U. 
The hnes marked ai/Si, q!2,32, and as ^3 are the first, second, and third 
order reflections respectively of the K^^ and i^^ lines of tungsten, the 
a line being a doublet. They are more clearly shown in figure 2, which 
was taken with narrower slits and greater distance of photographic 
i 
t 
c 
\ \ 
\ t 
FIG. 2 
plate from crystal, so that the doublet is clearly resolved. In this photo- 
graph the second order was given an extra exposure, which accounts 
for the apparent band in the middle. In the photograph of figure 1, 
all parts were given the same exposure. The wave-lengths of the lines 
are about 6% less than would be required by Mosely's formula. 
Slight deviations from the formula have already been noted for the K 
lines measured by Mosely and Maimer. All these lines, including tung- 
sten, can, however, be correctly represented by the empirical formulae 
va = 1.64 X 1015 2.10 foj. the a lines, 
and = 1.56 X lO^^ ]V 2 for the /3 lines, 
where v is the frequency and the atomic number. These formu- 
lae, while they have no theoretical significance, may be useful for 
interpolation. 
The bands which terminate on the long wave-length side at Agi and 
Ag2 are due to the silver in the photographic plate and are produced 
