230 €. Barns — Velocity and Struoiiire of the Nucleus. 



after the lapse of a definite number of minutes, give the 

 velocity sought at once, after correcting for the instantaneous 

 elevation of the plane of demarcation due to the withdrawal of 

 non-nucleated air from the top of the apparatus. The table 

 gives the ratios j)' /P ^^ pressures after and before exhaustion, 

 respectively. The experiments are very trying, chiefl.y because 

 of the difficulty of finding the initial position (time ^ = 0) of 

 the plane of demarcation between clean and nucleated air. For 

 this reason I will also give the height of the fog bank seen on 

 exhaustion after 50 minutes. The table shows that incidental 

 conditions (whether the inflowing filtered air be quite dry or 

 not, etc.), often very subtle, largely influence the results, but a 

 detailed explanation, for which there is no room here, must be 

 given elsewhere. 



Table II. 



— Apparent and corrected rates of motion (/c^ 



and k) of 



phosphorus 





nuclei in different saturated vapor 



s. 















Height of 



Pressure- 











fog bank 



ratio. 



Vapor. 



Apparatus, etc. 



/ci X 10'^. 



/ex 102. 



after 50"^. 









cm/min. 



cm/min. cm. 



•83 



Benzol 



Tower 



75 



61 



42 



•78 



Toluol 



Globe 



80 



62 



40 



•90 



a 



Tower 



43 



39 



21 



•83 



Acetone 



Tower 



58 



48 



32 



a 



a 



Initial rate 



75 



62 



38 



(( 



J Amyl 



Tower, initial ; 



100 



83 



51 



(( 



{ Alcohol 



apparent 



75 



62 



46 



u 



3 Ethyl 

 Alcohol 



Tower 



106 



88 



62 



<( 



Dried air 



72 



60 



51 



it 



Methyl 

 Alcohol 



Tower 



24 



20 



29 



(( 



Dried air 



64 



53 



42 



(( 



Water 



Estimated* 



10,000 



8300 







8. General comparison of nuclear velocities. — It will now 

 be opportune to make a comparison of all the nuclear veloci- 

 ties made in widely different experiments throughout my 

 work. I will begin with the results of my first memoirf on 

 the subject, in which the velocities of phosphorus nuclei in 

 ordinary atmospheric air were studied both by mechanical 

 methods (steam jet and absorption tubes), and by the electrical 

 condenser methods. The mean value of ^ = 18 cm./min. may 

 be taken. Hence in air, «: = 90 cm./min., nearly. The num- 

 ber of particles was of the order of n = 10* per cub. cm. of air. 



In more recent experiments and by a methodj of comparing 



* Rise or fall of the strands or fog filaments. 



f Experiments with Ionized Air; Smithsonian Contributions, pp. 1-93, 

 1901. 



X This Journal (4), xiii, p. 92, 1903. 



