104 A CONTINUOUS RECORD OF ATMOSPHERIC NUCLEATION. 



vacuum chamber. The experiments were now phenomenally successful. Thus 

 for the aperture s = 5 the mean results were n 150000, and for 5 = 4.6 (w g b p), 

 n = 140000. The precipitation of globules was clearly seen, and they persisted 

 even after the exhaustion was removed. The numbers being excessive and 

 referable to globules swept in by lateral air currents, an improvement was now 

 added by increasing the diameter of the disc p to about 5 cm. The improved 

 apparatus gave no results whatever, and the mere addition of the wider disc 

 wiped out all precipitation. But this capricious behavior is characteristic, for 

 next day drops were seen to fall as follows : 



5 = 4.5 w g b p n= 6.5X1 o 4 . 



4.6 wgbp 4.7 



6.3 wgbp 13.3 



after which no precipitation could be caught in the 6 subsequent exhaustions 

 by the identical method. The same unaccountable irregularity was noted in 

 the afternoon. Next day the first experiments showed 



5 = 6.0 w c g n = 7.3 X io 4 . 



6.4 wgvp 12. o 



etc. 



after which further precipitation did not occur. 



The apparatus was then again modified to the final form shown in figure i , 

 by inserting a thin brass tube laterally through the stopper, C, and firmly solder- 

 ing this tube above and below at e to the body of the microscope. A rod snugly 

 fitting this tube thus provided an eccentric focussing device, abed, with a stuffing 

 box at b, and an external handle at a. The latter is adjustable by aid of a set 

 screw so that the plate 5 may be kept in focus during rotation of the rod. To 

 catch the droplets, the plate s is rotated into the position s' quite beyond the 

 shield, for a definite time (15-30 seconds), and then returned to 5 for examina- 

 tion. In this way the definite results were obtained, in a manner to be further 

 detailed below, with the apparatus free from capricious behavior. It is of par- 

 ticular interest that the particles caught on the oiled surface persist as brilliant 

 round globules for a long time (sometimes io min. or more) in a saturated atmos- 

 phere. They very gradually vanish as a rule on the readmission of air into the 

 condensation chamber. 



To remove the globules for the next experiment, the influx of air is thus 

 not always sufficient. It is necessary to withdraw the microscope from the 

 condensation chamber bodily and to wave it about a few times in dry air. On 

 returning it to the chamber the plate is then again clear and white. 



At first the plate was oiled by a small flat piece of blotting-paper saturated 

 with oil and held on a stem, care being taken to remove all excess. Clean 

 machine oil or ordinary illuminating oil or a mixture of the two subserved the 

 purpose about equally well. Probably the best method of oiling consists in 

 dipping the plate rotated outward to s' in very hot melted vaseline (to drive 



