220 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
by a screw, and the front of the stage is cut away to enable them to be 
changed without shifting the focus of the substage. All condensers and 
illuminators are parfocal and centred to a standard, so that changes in 
the illumination can be accurately and rapidly made. The mechanical 
stage is double as fine in its motion as the usual type, and has horizontal 
travel of 3 in., and the fine adjustment is exceptionally delicate, each 
division of the milled head being equal to 0*001 mm. 
Microscopic Optics. 
Manguin, Ch. — Utilisation possible des diagrammes de diffraction des 
rayons X pour la determination complete de la structure du quartz. 
( Comptes Rendus , 1921, 17, 719.) 
De Broglie, Maurice. — Sur les spectres corpusculaires et leur utilisa- 
tion pour l’etude des spectres de ravons X. ( Comptes Rendus , 
1921, 23, 1157.) 
Pereira-Forjaz, M. A. — Etude spectrograph ique d’une meteorite 
portugaise. {Comptes^ Rendus, 1921, 23, 1170.) 
Pereira-Forjaz, M. A. — Etude spectrographique des minerauxportugais 
de tungsten. ( Comptes Rendus, 1921, 23, 1170.) 
Siegbahn, M. — Nouvelles mesures de precision dans le spectre de 
rayons X. ( Comptes Rendus , 1921, 25, 1350.) 
De Broglie, Louis. — Sur la theorie de l'absorption des rayons X par 
la matiere et le principe de correspondance. ( Comptes Rendus , 
1921, 26, 1456.) 
Dufour, Marcel. — Relation entre l’aberration et 1’astigmatisme pour 
un point situe sur l’axe d’un systeme optique centre. ( Comptes 
Rendus, 1922, 5, 288.) 
Coster, M. D.— Sur la serie L du spectre des rayons X. ( Comptes 
Rendus, 1922, 6, 378.) 
GEOLOGY, Etc. 
Primary Zones of Cornish Lodes. — E. H. Davison ( Geological 
Mag., Nov. 1921). Microscopic work has resulted in the view that the 
primary minerals in the Cornish veinstones occur in zones which change 
their character in depth : thus copper minerals give place to cassiterite 
(tin) on passing down the lode, and chlorite gives place to tourmaline. 
F. I. G. R. 
Dolomitization in Carboniferous Limestone. — L. M. Parsons 
(i Geological Mag., Feb. 1922). A number of microphotographs illus- 
trating various stages in the dolomitization process are given, from 
which the complex character of the material is evident. F. I. G. R. 
Interference Fringes and Focal Length of Objectives. — F. I. G. 
Rawlins {Phil. Mag., April, 1922). A logarithmic formula is deduced 
for Groth’s function. 
