TRANSACTIONS OF SECTION A. 403 
portion or recess in which a heating element is placed. The part of the tube 
immediately above this small vessel and its recess is constricted. The heating 
element may conveniently consist of a small coil of platinum wire wound round 
a suitable support; it may be placed in the recess of the small vessel or removed 
at will, without interfering with the vacuum of the lamp. The heating coil of 
wire is connected in series or in shunt, in the latter case being provided with 
an automatic cut-out. An external resistance is placed in series with the lamp. 
Before starting, the small vessel is full of mercury, which forms a continuous 
connection inside the tube between the positive and negative electrodes. When 
the electrical current is switched on, the heating coil becomes incandescent, and 
the heat given off by the wire goes to raising the temperature of the vessel and 
its contained mercury, there being no appreciable loss by radiation into the 
surrounding air. Very little heat is required, because the first bubble of mercury 
vapour formed rises to the constricted portion of the lamp and is there caught, 
thus breaking the continuity of the mercury inside the lamp and starting the 
arc. Owing to the resistance of the mercury vapour, which is formed once the 
arc is started, the current is cut down to the value required for running the 
lamp. The platinum wire of the heating element can be made of such a 
thickness, and the external resistance can be so adjusted, that the wire does 
not emit heat when the lamp is working, but becomes incandescent when the 
lamp is started, the action being quite automatic. 
6. The Transmission of X-rays through Metals, By H. B. Kuenr. 
A photographic examination of secondary Réntgen radiation leads to results 
of a different nature from those obtained by the ionisation method. When a 
narrow cylindrical pencil of X-rays is made to pass normally through thin rolled 
metal sheets, and fall upon a photographic plate placed behind and parallel to 
the sheet, some curious patterns are obtained. 
These patterns fall into two classes: (a) in which the central spot produced 
by the direct beam is surrounded by an irregular halo of smaller spots, and (0) 
in which the central spot is surrounded by faint extended patches forming a 
perfectly symmetrical pattern. The design varies with the metal. 
Class (a) markings are given by metal sheets which have been annealed, 
while the symmetrical patterns of class (b) are only obtained with newly rolled 
sheets which have not been annealed. It appears that the spots of the former 
are due to reflections from the microcrystals within the metal, while the 
symmetrical patterns of the latter are produced by the structure imparted to 
the metal in passing through the rolls. 
These star-like patterns are evidently analogous to those obtained when a 
beam of light passes through a crystal which appears streaky to the naked eye, 
the striations acting as a diffraction grating. (H. S. Allen, Nature, 91, p. 268. ) 
7. X, and the Evolution of Helium. 
By Sir J. J. Toomson, O.M., F.R.S. 
8. A New Elementary Constituent of the Atmosphere. 
By F. W. Aston. 
Sir J. J. Thomson has recently called attention to some results obtained 
with the method of positive rays which imply the probable existence of an 
element of atomic weight about 22. 
This point has been further investigated, and evidence has now been 
cbtained that atmospheric neon is not homogeneous, but consists of a mixture 
of two elements of approximate atomic weights, 19°9 and 22-1 respectively. 
Partial separation has been effected by fractional diffusion attested by a 
change of density, the latter being determined by a new and simple method. 
The two elements appear to be identical in all their properties except atomic 
weight. No change in the spectrum corresponding to the change of density has 
been observed. 
DD2 
