TRANSACTIONS OF SECTION A, 465 
2, On ‘ Reststrahlen’ and the Optical Qualities of Metals. 
By Professor H. Rusens. 
3. On the Separation of the Finest Spectral Lines. By Dr. O. Lummer. 
By the realisation of the black body and the experimental work during recent 
years on the black radiation our knowledge of the radiation laws has reached a 
certain point of completion. The constant of Kirchhoff’s law is as well known 
now for every wave length and every temperature as is necessary for any practical 
purpose. Having determined experimentally the laws of black radiation up to 
2,500° C., Pringsheim and I are now bringing in the radiation temperature scale 
based on these laws. The most important work now seems to me the study of the 
radiation from all bodies, especially gases, whether they conform to Kirchhoft’s 
law or not. To answer this promising question we must, in my opinion, study 
from the beginning the mechanism of gas radiation itself—energy distribution, 
These spectra consisting mostly of narrow lines, we must resolve these lines still 
further if we would draw conclusions about the existing mechanism. 
Led by these considerations, I began to work on the modern apparatus of 
high resolution, and I have brought with me the interference spectroscope, which, 
based on the interference fringes of a parallel glass plate, 1 worked out with 
Dr. Gehrcke; I am, therefore, able to show youits effect on the spectral lines pro- 
duced by a mercury-lamp. 
In our recent paper, published in the Reports of the German Physical 
Reichsanstalt, we gave the general theory of all apparatus of high revolving 
power, including the prism spectroscope, the grating, the Michelson echelon 
spectroscope, the interference spectroscope of Perot-Faby, and our own. 
Since the brilliant discovery of Zeeman we know the importance of apparatus 
with high resolution. Therefore, if we go further and put up apparatus of higher 
resolution, why should we not observe also the moving posztive electrons, if they 
can by any means be excited so as to produce light energy? And if the action of 
the electric field on the light is too small to be detected now, perhaps an apparatus 
of higher resolution may be able todo so. Be that as it may, only an apparatus 
of the highest resolving power can help us to enter into the molecule itself and 
give us new pictures of occurrences in the interior of an atom. Only by the aid 
of the most complete separation can we find the differences in the spectra of the 
so-called ‘homogeneous’ spectral lines, when, for example, we raise the tempera- 
ture of aradiant gas, or change the manner of exciting the electrons, using electric 
waves of a high or low period. 
Working in that direction with our interference spectroscope (demonstrated in 
the Cavendish Laboratory) we got some results which seem to us interesting, 
in so far as they show that vacuum tubes filled with mercury, hydrogen, sodium, 
helium, and argon, excited by Hertzian electric waves, give less well-defined inter- 
ference maxima than when excited by the induction coil. Discussing these un- 
expected phenomena, we are of the opinion that this loss of sharpness is not a 
consequence of the Doppler principle for several reasons; for example, because 
the intensity with Hertzian waves as the cause of luminosity is less than with 
the induction coil. We incline to believe that the Hertzian waves will enlarge 
the number of the many satellites of which, in our opinion, every line consists. 
Surely we can conclude that the excitement in a vacuum tube is not the result of 
heat, but of electrical occurrences. 
In my introduction I pointed out what important consequences this result has, 
in so far as we are not allowed to use Kirchhoft’s law for luminous bodies giving 
line-spectres, nor to draw conclusions from the brilliancy of these lines as to the 
temperature of the luminous gas. 
4. Recent Work at the National Physical Laboratory. 
By Dr. BR. T. Guazesroox, /.2.5. 
1904, HH 
