119 



to it the camera c, into whicli the li(|nid gas is poured and in which 

 it will be radiated by the Rönigen beam which is bounded by the 

 diaphragm (/ of tin (length 34 mm., diameter of the opening 2 mm.) 



shut by a leaf of ahimininm. The lower 

 part of the inner tube is narrow. First 

 it consisted of a small tube of alumininm 

 thick 0,015 mm. and with a diameter of 

 3 mm. which was soldered (o a copper 

 tnbe by means of wolframine. Later on this 

 ahimininm tube was replaced by a glass 

 tnbe thick 0,002^ to 0,01 mm. ') and 

 with diameter 2 mm., blown to a wider 

 glass tnbe. Except between b^ and i6, the 

 glass was silvered. 



The camei-a (radins 27,5 mm.) is fixed 



to the onter glass by means of a gronnd 



ping. In the camera along tiie cylinder 



wall the film ƒ is stretched (Eastman 



dnplitized A^-ray film) in the same way 



as was done by Dkbije and Scherhek. For 



taking in and ont the film, which was 



wi-apped up in black papei', the camera 



^'S' ^- was detached from the plate p to which 



its gronnd border had been cemented. The vacnum was obtained with 



a Langmuir condensation pump with (he rotating mei'cnry pump of 



Gaede as a forepnmp. This vacuum sufficed to ex()ose with one single 



filling of 200 cM' of the liquefied gas during more than 5 hours. 



Tiie Röntgen-rays were excited by a metal Siegbahn tnbe with 



Cu-anticathode. The K^ rays were filtered away by a Ni- plate of 



0,01 mm. The curient given by an inductorium with gas iriterruptor 



was ± 10 mA., tension ± 25 KV., time of exposition as a rule 



5 hours. 



For a photogra))h of the Rönigen interference figure of ice (see 

 ^ 3) we used a glass tube partly filled with water. The lower part 

 of this tube consisted again of a thin glass tube as described above. 

 The tube with water was let down into a vacuum vessel with a 

 lower part of thin-walled glass filled with liquid air. During the 

 exposition the tube was rotated from time to time. 



') These Ihin tubes of aluminium and glass aie proofs of the ability of tlie 

 amanuenses 1st class J. J. van deh Sluis and A. R. B. Gerritse, the last of 

 whom has also made several of the here mentioned photographs. 



