


































_ Fesrvary 3, 1923] 
; quencies of the light elements ra K-radiations plotted 
as ordinates against the atomic numbers as abscisse. 
‘he values for all the elements from magnesium to 
hromium which are amenable to crystal methods have 
been determined accurately with crystal gratings by 
Fricke, who measured the wave-length at the absorp- 
n discontinuity. They all lie on a curve which is 
most a straight line through the origin, and a few of 
n are shown thus, x. The aluminium value [-] is 
tically identical with Fricke’s for the same element 
and was obtained by Holweck by measuring the voltage 
Ve on an X-ray tube for which the absorbability in 
aluminium of the total radiation is a maximum. This 
ethod contains features which, though found separ- 
tely in the method used by Fricke and in the photo- 
pecs ic methods, are not common to both, and the 
‘agreement will no doubt tend to promote confidence 
] in the photoelectric methods. The points for oxygen 
meth), nitrogen (Foote and Mohler), carbon (Foote 
and Mohler, Hughes, Kurth, Richardson and Bazzoni), 
and boron (Hughes) have all been obtained by photo- 
electric methods. The hydrogen point A is the limit 
of the Lyman series which should correspond to the 
K level for hydrogen. It will be seen that the 
hydrogen, nitrogen, and o points practically 
fall on a smooth curve which is continuous with the 
for the elements from magnesium to chromium. 
e is some disagreement i in the case of carbon, but 
of the points are very close to the same curve. 
e only notable deviation is the low value given by 
The boron value also falls below this curve 
ut there is, so far as I am aware, no known reason why 
h frequencies should be a smooth function of atomic 
number for these very light elements. 
The next lower critical frequency for any element 
will umably be that pertaining to the L group, or 
the highest L critical frequency if there is more than 
‘one. The square roots of a number of such critical 
requencies for elements from boron to copper as given 
by photoelectric methods (boron and carbon, Hughes ; 
bon, oxygen, aluminium, silicon, titanium, iron, 
nd copper, Kurth) are shown thus, x, in Fig. 3 (p. 120). 
frequencies should be somewhat higher than those 
lof the corresponding lines, and it will be seen that the 
Dbserved points from aluminium to copper are all 
abo t the same distance above the broken projection 
the curve through the values for the L,, lines for 
tl e elements from zinc to zirconium obtained by 
pnes. 
= 
Bat 
Pror. JOHANNES ORTH. 
“Piss JOHANNES ORTH, whose death is an- 
nounced, was born in 1847 at Wallmerod in 
Nassau. He received his medical and scientific training 
“chief at Bonn, where he studied pathology under Rind- 
, Whose assistant he afterwards became. Later, he 
"was appointed assistant to Virchow in Berlin. In 1878 he 
was appointed professor of general pathology and patho- 
anatomy in Géttingen and afterwards received 
the title of Geh. Med.-Rat. In 1902, on the death of 
Virchow, he was elected to the chair of pathology in the 
_ University of Berlin, and since then his energies have 
_ NO, 2779, VOL. 111] 
Es 
NATURE 
155 
fication for extrapolating from the zirconium to zinc L,, 
values to the value for the L, line for aluminium as 
was done in interpreting Millikan’s vacuum grating 
data, It will also be observed that the values of the 
limits for boron, carbon, and oxygen given by the 
photoelectric methods are either very close to the 
values for the shortest lines in the L spectra found by 
Millikan or have a somewhat higher frequency. These 
properties are in harmony with those found in what is 
more usually regarded as the X-ray region. It should 
be added that data for elements between sodium and 
chlorine have been given by Mohler and Foote, which 
fall on or below the L, curve as drawn in Fig. 3. These 
data, however, have been obtained by the electron 
bombardment of vapours, in many cases of compound 
vapours, and it is not improbable that the values for 
these will be different from those for the solid elements. 
Some of these data also appear to refer to radiation 
potentials, which correspond to lines, rather than to 
ionisation potentials, which correspond to limits. 
Just as in the case of the L, lines, the L limits for 
the light elements from helium to magnesium do not 
change smoothly with increasing atomic number as do 
the limits for the heavier elements. In fact the 
frequency for helium as obtained either by direct 
determination of the end of the corresponding spectrum 
or from the ionising potential is higher than that of 
succeeding elements until carbon is reached. 
In the case of a number of elements ranging from 
aluminium to molybdenum, critical potentials have 
been observed (by Kurth and by Richardson and 
Bazzoni) at values corresponding to frequencies well 
below those which characterise the L spectra. The 
connexion with the generally recognised X-ray series of 
the heavier elements has scarcely yet been worked out 
in sufficient detail for the precise group allocation of 
some of these to be determined with certainty. 
Turning to Fig. 1, C, D, and E show, on the same 
scale as in A and B, the position of some of the spectral 
limits given by these photoelectric methods. It will 
be seen that a majority of them lie in the gap between 
16°35 and 17°38 in which so far no spectral lines, either 
X-ray or ultra-violet, have been detected by grating 
methods. If the interpretation of these photoelectric 
determinations as the ends of the various spectra is 
substantiated, it will have to be admitted that the gap 
in the spectrum between the ultra-violet and the X- 
ray region about which I have been speaking is not 

fystal measurements. This affords additional justi- | merely disappearing but has actually disappeared. 
Obituary. 
been devoted chiefly to the development of the Institute 
of Pathology, which was founded and equipped by 
Virchow. 
Orth was the author of numerous papers on patho- 
logical subjects, and also of several books, the two most 
important of which were his “ Compendium der 
pathologisch-anatomischen Diagnostik,” which was 
translated into English in 1878, and his “* Lehrbuch der 
speciellen pathologischen Anatomie,” published in 1893. 
Orth was undoubtedly a pathologist of great eminence 
and made many valuable contributions to his subject, 
but his reputation rested rather on his powers as a 
teacher and expositor and on his width of knowledge 
