[shaver] spectra of ARGON 137 



prevented the wax from melting. Exhaustion was carried on for 

 about twenty hours by means of a mercury pump and also a charcoal 

 tube immersed in liquid air, the temperature of the furnace being 

 maintained at 400°C. The filament was also heated to incandescence 

 by passing a current through it while the lamp was being exhausted 

 so that any gas which might be given ofï was removed. The argon 

 gas was purified from a mixture of 80 per cent, argon and 20 per cent, 

 nitrogen by repeatedly passing it over calcium turnings heated to 

 600°C., and after the pump and the charcoal tube were sealed off, 

 some of this purified gas was admitted to the tube. The best gas 

 pressure for the production of the arc was found by trial to be about 

 . 1 mm. of mercury, after which the lamp was sealed off and ready 

 for use. 



The electrical connections are also shown in Fig. 1. The current 

 for the heating circuit was supplied by a 20 volt battery Ex, which was 

 connected in series with a variable resistance Ri, an ammeter A, and 

 the filament F. The grid voltage was obtained from a second battery 

 E'i, which was short-circuited through a resistance R^ of about 115 

 ohms. Any voltage not exceeding 240 volts, the maximum of the 

 battery, could be applied between the filament and the grid. 



III. Experiments 



The heating current required to bring the tungsten filament to 

 the temperature necessary for the emission of electrons was at first 

 5.8 amperes, but as the filament gradually evaporated and thus 

 decreased in diameter this amperage was reduced by increasing the 

 resistance R\ so as to keep the electron supply constant. The electrons 

 were given a definite speed depending on the grid voltage while travers- 

 ing the distance between the filament F and the inner cylinder of the 

 grid. Any electrons which passed through the meshes of the inner 

 cylinder then entered the fieldless space between the cylinders, since 

 the latter were connected by iron wire as previously described. When 

 the grid voltage was sufficient to give the electrons the energy required 

 to cause inelastic impact with the argon atoms, radiation was produced 

 in the space between the cylinders. This was focussed on the slit 

 of a large quartz spectrograph made by the Adam Hilger Company 

 and photographed on Wratten panchromatic plates. It was found 

 that with an exposure of half an hour good photographs were obtained. 

 The current passing from the filament to the grid was kept as near to 

 35 milliamperes as possible, except in the case where the grid voltage 

 was 10.1 volts when it fell to 10 milliamperes. 



