

12 EXI'KIUMKNI*; WITH ]UXIZK1» AIK. 



14. Xnnj iuni^ers. — This expeiiiueiit suggested the efficient nietlioJ of 

 adjusting an X-ray duster, as the X-iay tube did not easily leart on the naked jet. 

 The phm, in other words, is to ionize tlie air within a spacious hell jar, by X-liflit, 

 and then to carry the nuclei so produced into the color tube C by convection. 

 In figure 18 (drawn to a smaller scale), B is the X-ray tube (Bow^doin pattern), 

 enclosed in a cylindrical l)o.\' of tin plate, D, with a removable lid, E, and an 

 aluminum window at Al. The terminals /f are enclosed in glass tubes filled with 

 paraffine, and their exi)osed ends 52 inches apart to avoid brush action on the 

 color tube C. The tube radiates through the winddw into tlie bell jai' ^1, and 

 may even be placed over 18 inches above its mouth. The action of this dust pro- 

 ducer is intense, and the field opaque when the current passes. Phosphorus placed 

 within the cylinder D is quite ineffective, showing that no direct leakage occurs 

 out of it. The usual experiments may be made. A tin plate sci'een between the 

 window and jar cuts off all rays, an aluminum screen almost none. The steam 

 pressure of the jet may be I'educed until steam just passes. 



15. Fersistenee of imelei. — The same method may be modified to test the 

 persistence of nuclei, particulai'ly in the case of pliospht)rus. The apparatus is 

 shown in figure 19, consisting of the large bell jar, A, closed loosely by the litl B, 

 so as to admit of a circulation through the jar when the cotton pluf IJ is 

 removed. The contents then discharge into the color tube C. P is the o-lobule 

 of pho.'<2>horus on a wire stem, which, like the plug, can be inserted into A and 

 withdrawn easily through stoppeied tubulures in the lid. 



With the valve open and P in place, the field is always opaque, a test whicli 

 was made throughout the exi)eriiiient8. The following results indicate the 

 coloring power of the contents of the jar at different times after the phosphorus 

 was suddenly removed. Removal of the lid showed a blue color lasting fifteen 

 seconds. 



Time .ifter removing. Color in lube. Duration (time to empty the vessel). 



15 sec. opa(|ue. 10 sec. 

 30 " dark blue-gray blue. 10 " 

 60 " smoky brown. 



[30 " opaque-blue. 15 " l 



60 " smoky blue-gray. 10 " J 



120 " flash of darkness. 



180 " j gray-green flash when 



180 " (lid wadded). ( lid is removed. 



20 ' opaque to blue. 



180 flash of darkness. 



These data show that even after three minutes enough dust is left to make an 

 impie.ssion on the color tulie ('. 'i"he a})parent decay, however, is marked, and 

 even during the time taken in emptying the ves,sel (10-15 sec), the attenuation is 

 apparent. Colors so produced, UKU'eover, are not clear. 



10. Ci)-effic'u'nt of (Iccaij. — Taken in connection with the results of the next 

 chapter, the present experiments admit of a preliminary estimate bearing on the 



