14 KXPERIJIENTS AVITII lONTZEI* AHt. 



may he made by passing dust-ladeii air tiiroiigh considerable lengths of wide 

 tubing. Drain pipe made of tin plate is admirable for tliis purpose, one end being 

 left open and the other joining the color tube. This is shown in figure 20, at D, if 

 the vessel A is removed. Stoppered holes, p, at different distances apart admit 

 the phosphorus particle. The following results wei-e found with tubes 2 inches 

 in diameter and as much as 60 feet long. The draft in the influx tube being 

 actuated by the jet dejiends on the steam pressure. It may be reduced by opening 

 the bottom of the tube 6'. The first series of values Avere found with a pellicle of 

 phosphorus placed in the tube at different distances, D, from the jet. 



The persistence of dust nuclei is thus again a question of minutes, for in the 

 time of transfer through these long tubes at the slowest velocities obtainable (lower 

 window of color tube opened for this reason), the color effect still survives, though 

 with diminished visjor. 



The woi-k was afterwards repeated, with extremely small steam pressures but 

 relatively wide jets (-^ inch), introducing an abundant flow of steam nearly at 

 atmospheric pressure. The time of passage through the tubes and the duration of 

 the color due to an instantaneous introduction of the pliosphorus pellicle at the far 

 end were also noted. Mixture and diffusion occui' during the passage. The tube 

 lengths were 54 to 60 feet. 



■o' 



(i) Flash at far end lasts 10 seconds at near end. 



(2) Time of passage. Color. 



30 sec. Not changed perceptibly. 



60 sec. r Darkness (opaque field) intense. 



40-70 sec, diam. jet .45 cm. < Phos|)horus inserted in far end a few seconds 



60-90 sec, diam. jet .75 cm. (. only. Effect prolonged at near end as shown. 



Thus the increased supply of low-pre.ssure steam (wide jet) has much enhanced the 

 sensitiveness of the apjiaratus, thougli color, as such, no longer aj)peai:s. The time 

 of passage obtained in this way (90 seconds in the maximum) is below that of the 

 preceding experiments with bell jars. The gradual lengthening of the dust-laden 

 column of air is due to the eddying mixture in passage. 



18. Persistence of X-ray niu:lei in long tubes. — With the addition of the 

 vessel A, figure 20, and the adjustment of figui-e 18, the foi-mer ariangeraent was 



