SECTIONAL TRANSACTIONS.—A, G. 285 
The fluctuations appear to be electromagnetic, and may be allied to other 
known forms of electromagnetic oscillation. 
Description of a new method by which the fluctuations are autographically 
recorded, and correlated with changes in the elastic properties of metals. 
These records indicate that the modulus of elasticity of metals is not a 
stable but a fluctuating property, the fluctuations being periodic in character, 
and capable of being induced by magnetic disturbances, including the action 
of stray fields. 
Mr. O. A. SaunpEerS.—Convection in gases at high pressures. 
Theoretical considerations show how the effect of pressure on natural 
convection in gases may be related to that of linear size. ‘The heat losses 
from large surfaces in gases at atmospheric pressure can therefore be deduced 
from small scale experiments at high pressures. Some experimental results 
are discussed. 
Mr. H. ve B. Knicut.—Industrial application of Thyratrons, with special 
reference to the control of resistance welding. 
The Thyratron is a gaseous discharge device through which current 
flows in the form of an arc and in which the current flow can be controlled 
by means of a control electrode or grid. A large range of such devices is 
available, with ratings varying from a fraction of an ampere to 100 amperes 
or more. These currents can be controlled with a negligible amount of 
controlling energy ; and, especially in high voltage circuits, the Thyratron 
provides an easy means of controlling considerable power. 
Particular reference is made to the application of the Thyratron in con- 
nection with resistance welding. In modern resistance welding applica- 
tions some metals can only be welded satisfactorily if the welding current 
is of very short duration. In addition, modern production methods require 
very high-speed operation with precision and reproducibility. ‘These 
features are practically impossible to obtain when electromagnetic relays 
and contactors are employed to control the welding current ; but they are 
easily obtainable by the use of the Thyratron. 
A single impulse Thyratron-controlled spot--welder for pedal operation 
will be described and demonstrated. 
Mr. L. J. Davies and Mr. J. H. MitcHeLt,.—Resonance radiations in 
electric discharge lamps. 
This paper aims at showing the importance of the phenomena of resonance 
radiations in connection with the nature of the light output from various 
types of electric discharge lamps. 
The resonance and general emission spectra, together with other physical 
properties on various elements, are discussed with a view to their possible 
utilisation in discharge lamps ; in particular resonance phenomena for the 
cases of mercury and sodium are dealt with in detail. 
Mr. H. R. Rurr.—The commercial production and utilisation of ultra-violet 
radiation. 
The large scale utilisation of ultra-violet radiation for such purposes as 
artificial lighting, manufacture of special chemicals and sterilisation of 
food-stuffs, utensils, and the water of swimming baths is assuming a rapidly 
increasing importance. 
