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XLY. On an X-Ray Bulb with a Liquid Mercury Anticathode^ 

 and on Wave-Length Measurements of the L- Spectrum of 

 Mercury. By Alex Muller *. 



[Plate XIV.] 



1. Introduction. 



AFE W years ago, when the writer was working with a 

 special type of X-ray bulb suitable for spectroscopic 

 work, faint lines, which belonged to the L-spectrum of mer- 

 cury, appeared quite unexpectedly on many of the plates. 

 The mercury vapours from the Gaede pump, with which 

 the bulb was exhausted, had apparently diffused into the 

 discharge space and condensed on the anticathode, a rather 

 surprising fact considering the heating effect of the cathode 

 rays. 



In this particular X-ray bulb the anticathode was placed 

 in a narrow tube of about 10 mm. diameter. Once in this 

 tube the mercury had a relatively small chance of escape. 

 Preliminary experiments which had been made in the Physi- 

 cal Laboratory of the University in Geneva by the writer, 

 showed that it was quite easy to get fairly hard and intense 

 X-rays using directly a liquid mercurjr anticathode, a fact 

 which opened the possibility of obtaining the X-ray spectrum 

 of mercury. The following investigations have been carried 

 out in the Cavendish Laboratory in Cambridge. 



The strongest mercury lines have been measured by Sieg- 

 bahn in his systematic work on X-ray spectra, using the 

 mercury in the form of a salt which was rubbed on the 

 surface of the anticathode. In the case of mercury this kind 

 of procedure is not very efficient, at any rate if one does not 

 use a specially designed X-ray bulb, on account of the fact 

 that the mercury salts are very volatile. It seemed to be 

 worth while to complete the previous measurements of the 

 L-spectrum of mercury mainly with the purpose of showing 

 the efficiency of the arrangement which has been used in this 

 work. The fact that materials with fairly high vapour- 

 pressure can be used as anticathodes may be useful for future 

 work on X-rays. 



2. Description of the Bulb (fig. 1). 



The bulb consisted of three parts which were joined 

 together by soft wax. The discharge chamber A consisted 



* Communicated by Professor Sir E. Rutherford, F.R.S, 

 2 F 2 



