﻿Coloured Cloudy Condensation. 2\) 



atmosphere artificially, utilizing the tube F, fig. 1, containing 

 phosphorus. The results for this case are not without com- 

 plexity, but the character of the effect produced is obvious at 

 once : it takes but a trace of the phosphorus- tainted air to 

 make the field permanently opaque at all pressures and tem- 

 peratures not unreasonably high. In other words, the tendency 

 is to drop the blue-opaque curve of the above figures into 

 coincidence with the abscissa. One would surmise that at 

 least the asymptotic portion of the yellow-opaque curve would 

 likewise drop to the abscissa, and this is actually the case, as 

 will be shown presently. By allowing the discharge from F 

 to take place into E through a glass tube only a few milli- 

 metres in diameter, while the air-tube C is fully two inches in 

 diameter, I was able to dust the air sufficiently to obtain at 

 least the approximate contours of the corresponding relation 

 of steam-pressure and air-temperature. The data are inscribed 

 in fig. 4, and together they make up the curve P near the 

 axis of temperature. Thus the striking potency of even 

 traces of dust is well exhibited. 



Clearly the rudimentary curve P is a member of the same 

 family to which AB belongs, and it is therefore obvious 

 that the whole field between B and the abscissa is a region of 

 temperature and pressure loci *, each of which corresponds to 

 a particular value of dust-contents. Since, therefore, the 

 accuracy with which the point can be located at any (mean) 

 temperature is about 1 cm., the apparatus ought to register about 

 40 degrees of dust-contents between normal atmospheric air 

 and the artificial mixture stated. On this scale the variation 

 of the dust-contents of normal air | lies in the interval between 

 40 cm. and 50 cm. of mercury, remembering that the height 

 of the asymptote (virtually reached at 28° to 30°) is taken 

 for registry. 



12. To bring out the conditions more fully, however, it is 

 necessary to make supplementary tests both with phosphorus 

 and with filtered air. 



If the basket of phosphorus is placed in the tube E (fig. 1) 



* Probably the best method of actually mapping out these curves will 

 consist in using- nozzles of different degrees of smoothness. By mere 

 haphazard drilling and polishing of such nozzles, I obtained curves 

 between asymptote 20 cm. and asymptote 50 cm. That these curves will 

 be identical with the corresponding dust-curves is made probable by §16 

 below. 



t Supposing that the possible errors have been correctly apprehended. 

 In experiments made throughout the entire month I was surprised that 

 an apparatus so sensitive to artificial dust should show such slight mean 

 variations of the dust-contents of atmospheric air from day to day. 

 Witness the above curves. 



