SECTIONAL TRANSACTIONS.—A, A*. 277 
magnitude and red-shift, which represent the type of relation which can be 
tested by observation. 
Mr. H. G. Howe._i.—Recent applications of spectroscopy (10.30). 
Now that the importance of the presence of small amounts of metallic 
impurities in alloys has been recognised, the practice of quantitative 
spectrum analysis is receiving much attention. The internal standard 
method involving a determination of intensity ratios is considered to be the 
most accurate, although for higher percentages of impurity the Barrett twin- 
spark method is preferable. 
The intensity ratio can be measured conveniently by using a rotating 
logarithmic disc. 
The biologist and medical research worker are using the spectrograph to 
determine the influence of minute traces of metals in the blood and spinal 
fluid, in plants and living organisms. 
Absorption spectrophotometry is providing much useful data about the 
equilibrium of certain chemical reactions which cannot be obtained by 
chemical methods. 
Absorption measurements have been of great importance in work on 
such obscure organic compounds as the vitamins. The spectra of hamo- 
globin and its related compounds are being extensively studied with a view 
to correlate changes in spectra with changes in chemical constitution. 
It has been reported that the absorption spectrum of the plasma of the 
blood of normal rats is different from that of those suffering from cancer, 
and that marked changes take place in the absorption curves at the approach 
of death. 
DEMONSTRATIONS (continuously for the period of the meeting) :— 
Mr. C. R. BurcH.—Prof. Zernike’s phase contrast test. 
An F/6 paraboloid is shown, the test being made null with the aid of a 
figured compensator. The errors of spherical aberration, coma, and 
astigmatism can be shown by changing the adjustments: zonal error can 
be shown by inserting a figured ‘ error-plate.’ 
Mr. L. H. J. Puitiips.—Prof. Zernike’s phase contrast method of 
microscopic illumination. 
The apparatus for this demonstration was kindly lent by Prof. Zernike. 
DEPARTMENT OF MATHEMATICS (A*). 
(Prof. E. T. Wuirraker, F.R.S., in the chair.) 
Thursday, September 6. 
Discussion on The electronic theory of metals (10.0) :— 
Prof. R. H. Fowier, F.R.S.—The quantum theory of metals. 
General introduction. Electron distribution laws ; the Fermi function. 
Thermionic work function and photoelectric threshold of an ideal metal. 
The free path phenomena; Sommerfeld’s elementary discussion for an 
