48 Transactions of the Royal Society of South Africa. 
In order to pass a bearo of Eontgen rays through this layer of crystal- 
Hne solution a cylinder similar to that used by Friedrich and Knipping 
was used. The openings in the diaphragms were 5 and 3 cm. respectively. 
This cylinder was placed in front of the crystalline solution, and two 
photographic films (at a distance of 3-5 cm.) behind it. This is to avoid 
faults " and spots of the films in case they are not perfect. 
The spirals were clamped between the pole pieces of a Max Kohl 
electromagnet, after some wadding had been glued on the conical pole 
pieces in order to avoid heating them. 
B B ^2 
Ai CO 
Ai and kn. Ampmeters. 
Gi and G^. Galvanometers. 
Ei, E.2, and E.. Variable resistances. 
BB. Terminals of heating coils. 
CC. Terminals of electromagnets. 
EE. Terminals of thermocouple. 
A good microscope with Nicols was fixed on to a brass holder, which 
rested on the coils of the electromagnet. 
When the microscope with its holder is placed over the magnet, then 
the pole pieces were between the objective and the object table; thus the 
solution between the spirals could be examined without any trouble. 
During the time of exposure the microscope is removed and the whole 
of the apparatus covered in between sheets of lead so that only radiations 
which had passed through the solution could reach the films. 
