32 
PHYSICS: D. L. WEBSTER 
Proc. N. a. S. 
185. This line shows well at high voltages, and faintly but distinctly 
when \min = 1.01 A. This places it 
^Q. In the calcite spectrograms taken at Harvard there is a faint com- 
panion of 1S5 at a wave-length greater by 0.010 =•= 0.002 A. This also shows 
in some high resolution mica films, where the tube was 3 meters from the 
mica instead of 75 cm., and in a few of the low resolution mica films, at 
X^.„ = 0.88, 0.910 and 0.945 A. In all the others is wide. The fact 
that it shows as low as 0.945 A places it in Li, and its intensities in the cal- 
cite films indicate that it follows qualitatively the constant intensity ratio 
law. At least it does not violate it in any such way as an L2 line would 
when compared with an Li. Since (S^, and are both in Li their wave- 
length difference would be nearly the same in tungsten as in platinum. 
/Se is, therefore, probably the analogue of the tungsten line discovered by 
Dershem and given by Overn as 1.2212 A, jSs being his line 1.2097 A. 
jSi. This line belongs to L2 and gave the most definite results by ioniza- 
tion for determining X^^- With the present h this^is 0.935 =•= 0.004 A. 
The films show ^1 plainly at 0.910 A, but not at all at 0.945 A even in the 
third order. 
rj. The third order of this line unfortunately coincides with the fourth 
of 72, which belongs, as noted below, to L2. But the fourth order is faint 
and the third strong, and the fourth 71 which is very near 3 r] and 4 72 
is but very little stronger than they. Since 3 71 is much stronger than 
3 72 this means that most of the intensity of this combined line is that of 
3 ??. Now the combined line and 4 71 show the same intensity ratio, as 
nearly as one can tell, at all voltages, and are visible down toX^^„ =0.910 
A, but not at 0.945. At these low voltages 4 72 alone would certainly be 
invisible, and if rj and 71 were not in the same series the change in their 
ratio would be unmistakable even with no measuring instruments. Hence, 
we may fairly confidently assign 17 to L2. 
^4. This line gave results by ionization showing a critical wave-length 
0.935 ± 0.02 A, the accuracy not being equal to that obtained with jSi 
because it is rather faint. The films, however, show a faint line in this 
position even at X^^^ = 1.01 A, far below the critical potential of L2. 
This is probably the same as a line which is just resolved from Pt 184 in the 
calcite and high resolution mica spectrograms. It is called Ir ^2 because 
its wave-length is that of the iridium line and it obviously does not belong 
to L2. But as all lines are rather wider in the mica photographs and the 
work of Dershem and Overn showed a line in tungsten that might be 
near this point in platinum, further work with a high resolving power and 
long exposures is needed. As the present spectrograph is unsuitable for 
this and several other problems presented by the very faint lines, a more 
suitable one is now being constructed by Mr. F. C. Hoyt. 
Ir jSi and Ir ^2- These lines appear in the calcite and high resolution 
