352 SECTIONAL TRANSACTIONS.— G. 



which are used under conditions of mechanical shock and vibration. The paper 

 seeks to examine the subject comprehensively ; to state the facts now established by- 

 research and experiment ; and, finally, to define the path of future progress. 



Under ' General Considerations,' the subjects of light efficiency, and the use of 

 gas, spiralised filaments, and anti-vibration fittings are briefly considered. 



A second section on ' The Metal Filament ' deals with the subjects of grain growth 

 and grain size, effect of stress on deformation and fracture, effect of vibration, the 

 transition temperatures of tungsten, and the effect of temperature and intensity of 

 vibration. From metallurgical arguments, it is concluded that a filament is always 

 weaker when hot than when cold. Large crystals are desirable in order that crystal 

 growth may be minimised and ductility increased, although it is pointed out that the 

 use of large crystals does not necessarily mean increased strength, owing to fracture 

 being generally intra-erystalline. 



In a third section, particulars of practical shock tests of lamps are given, together 

 with a view of the automatic shock-testing machine used. As a result of a large 

 amount of shock testing work on various types of lamps, it was conclusively demon- 

 strated that a lamp is weaker when burning than when cold, the weakness being due 

 to failure of the filament which may fracture, short-circuit, or sag. The chief factor 

 governing mechanical strength is the nature of the filament ; and other factors, such 

 as the geometrical arrangement of the filament, the type of mounting, and the general 

 design of the lamp, are secondary. It was found that spiralised filaments are not 

 necessarily stronger than straight, and that in a gas-filled lamp any added strength 

 due to the damping effect of the gas is negligible. 



The fourth, and final, section states briefly the conclusions and recommendations. 

 It is argued that although high temperature tends to weaken a filament, it is a 

 retrograde step to obtain added strength by lowering the temperature, and therefore 

 the light efficiency. Greater strength must be attained by better filament structure 

 and not by resorting to uneconomic operation. A general adoption of the spiral 

 form of filament is deprecated until the success of the low-consumption gas-filled lamp 

 is established. Until then, the straight filament vacuum type lamp is advocated for 

 low-consumption lamps, and a squat squirrel-cage form of mounting is advisable. 



Since the mechanical strength of a lamp largely depends on the nature of the 

 metal filament, the user is essentially concerned with all investigational work having 

 for its object the improvement of the filament. Hitherto he has known little about 

 the filament for which he is paying. It is suggested that advantages might accrue 

 to both the large user and the manufacturer by indicating on the lamp bulb the type 

 of filament used. A method of symbols could be adopted similar to that which works 

 successfully in the carbon-brush industry. Although such a system would not tell 

 the user much about the filament, it would give him an assurance that he is buying a 

 known article, the qualities of which have been determined, or a new article, the 

 qualities of which he may then compare with those already known. The user who 

 wishes to co-operate would, at any rate, be in a position to add his practical experience 

 towards the attainment of the desired ideal. 



Dr. J. Hartmann. — The Jet Wave Rectifier. 



Mr. F. C. Turner. — A Thermionic Valve Type Close Voltage Regulator. 



The paper describes a method of automatically controlling the voltages of D.C. 

 generators within fine limits. 



The load on a generator consisting of constant temperature furnaces and fatigue 

 testing machines running for long periods is described, and the effect of changes in 

 the generator voltage considered. It is shown that for his special caste the allowable 

 variation is of the order of plus or minus 0-5 volt in 200. 



Alternative methods of maintaining constant voltage are discussed, and are shown 

 to generally permit too large a variation and to be comparatively expensive. The 

 evolution of a thermionic valve operated relay is described which gives control of the 

 desired order at a moderate cost. A double element regulator capable of controlling 

 within plus or minus 003 volt is explained. A description is given of the design and 

 operation of a heavier time lagged relay and rheostat control, worked by the fine relay. 



The behaviour of the complete regulator over a considerable period is dealt with, 

 and possible modifications of control mentioned. The paper is illustrated. 



