CHAPTER I. 



RESULTS WITH AN OBJECTIVE METHOD OF SHOWING DISTRIBU- 

 TIONS OF NUCLEI PRODUCED BY X-RAYS, FOR INSTANCE.* 



1. Introductory. By passing the X-rays into one end of a long rec- 

 tangular (virtually tubular) condensation chamber and observing the 

 effect produced after successive different intervals ot time by the 

 condensation method, evidence, with a possible bearing on the origin 

 of these nuclei, was obtained. The coronas are distorted and at first 

 occur on the bulb side of the apparatus only. The distribution of 

 nuclei is inferred from the form of the corona. 



The experiments described were all made with strictly dust-free air, 

 as both the method of precipitation and of filtration were applied prior 

 to each experiment. Furthermore, as the exhaustions necessitated 

 the use of short lengths of rubber tubing (}4, Y\, and i inch in bore 

 in the different cases), the amount of sudden cooling obtained does 

 not directly correspond with the pressure difference, 8/>, owing to the 

 resistance of the tube to the flow of air. The data, 8p, thus refer to a 

 given type of apparatus, but they are satisfactory as relations, so long 

 as this is not changed. Furthermore, the pressure difference was so 

 adjusted as to entrap all X-ray nuclei, to the exclusion of the normal, 

 quasi-molecular nuclei of dust-free air, or at least of such nuclei for 

 which a packed-cotton filter is no barrier. 



2. Apparatus. The method was purposely reduced to extreme 

 simplicity, and the apparatus is shown in figure i. A B is the long 

 rectangular condensation chamber of wood impregnated with resinous 

 cement. The front and rear faces are plate glass, through which the 

 coronas may be observed. The other sides are lined within with thick 

 cotton cloth, kept wet, and there is a layer of water at the bottom to in- 

 sure complete saturation of air. C is a stopcock leading to an efficient 

 filter (not shown). Supersaturation is produced by sudden exhaustion 

 at the B end of the apparatus, while the A end receives the radiation 

 from the X-ray bulb, X. A large vacuum chamber was placed in 

 connection with the exhaust pipe shown, through a wide stopcock, 

 the details of which need not be explained. The X-rays used were 

 not very penetrating, and were obtained from a soft bulb actuated by 



* Much of the experimental part of this chapter was carried out by Mr. Robinson 

 Pierce, jr., and myself, conjointly. 



