408 



Dr. F. P. Kerschbaum : Interference 



containing the frequency which is capable of exciting the 

 Hg- resonance radiation in very high intensity and con- 

 tinuously *. 



On the Velocity of the Diffusion of Hg-vapour at 

 room temperature. 



The apparatus, described above, will only work satisfac- 

 torily if it is possible to maintain the partial pressure of the 

 Hg in the chamber (Y) under 0*00001 mm., while in the 

 chamber (R) this pressure is 0*001 mm., the partial pressure 

 of air in both chambers being under 0*00001 mm. The Hg- 

 vapour which diffuses through the slit (s) is to be condensed 

 by liquid air. Is this diffusion slow enough compared with 

 the velocity of the condensation for the dimensions of our 

 apparatus ? 



This question was decided by the following experiment, in 

 which we use the extraordinary facility with which resonance 

 radiation is scattered, i. e. apparently absorbed by saturated 

 Hg-vapour at room temperature. 



A brass cylinder (???) (fig. 4) of 3 cm. length and 3 cm. 



Fiff. 4. 



Charcoal Liquid air 



tube 

 and Caede pump. 



diameter is closed at both ends with quartz crystal plates 

 cemented on with sealing-wax. Along the axis the cylinder 

 is divided into two halves (A) and (B) by means of a brass 

 plate (W). Into this partition wall a slit (s) is soldered of 

 the same dimensions as used in the interference apparatus. 

 The halves (A) and (B) are therefore only connected by a 

 slit of 0*02 mm. width, 12 mm. height, and 15 mm. length. 

 The slit (s) is shown horizontally in fig. 4. Two brass tubes 



I intend to publish shortly a detailed account of the construction of 



* I intend to publish shortly a detaile 

 this lamp and the properties of its light. 



