IN THE PEESENCE OF DUST-FEEE AIE AND OTHER OASES. 
297 
Supersaturation required to cause Condensation in air at different 
temperatures. 
h- 
0 ,. 
TT). 
7- 
0JO,. 
b- 
TTo. 
S = -"-1 ffiV 
^■3 V^o/ 
155 
285-5 
13 12 
1-252 
1-41 
1-097 
- 10 
2-197 
4-35 
20 ^ 
293 
17-39 
1-252 
1-41 
1-097 
— 5-8 
3-02 
4 2 
28-8 
301-8 
29-45 
]-252 
1-41 
1-097 
+ 2-2 
5-377 
4-0 
Thus the maximum supersaturation is 4'35 at — 10° C, and 4'0 at + 2'2°C. It 
therefore diminishes with rising temperature at the rate of about ’03 per degree. 
Superstatmntion recpdred to produce Clouddike Condensation. 
The calculations are again made for an initial temperature of 20° C. 
The results for Air, Oxygen, Hydrogen, and Nitrogen are grouped together, the 
difference in the observed value of Po/y^ when the dense condensation begins being no 
greater than can be accounted for by experimental errors. In all these gases the 
least value of Pj/pi when the condensation first becomes cloud-like is about 1’38. In 
air, however, in which more exact measurements were attempted, the beginning of 
the change from the rain-like to the cloud-like form could be detected when Po/y^ 
only slightly exceeded 1'37. 
The calculations have therefore been made taking vjiiy = 1’375. /[ = 20° C. 
^1- 
V.PVy 
7i- 
opo,. 
b- 
.S = /fiV. 
TTo [voj 
Air, 0, H, N . . 
293 
17-39 
1-375 
1-41 
1-140 
- 15-8 
1-41 
7-9 
COg. 
293 
17-39 
1-.53 
1-31 
1 141 
- 16-2 
1-37 
7-3 
(Chlorine . . 
293 
17-39 
1-44 
1-3-2 
1-124 
- 12-3 
1-83 
5-91 
/ 
If then by sudden cooling a supersaturation exceeding 7‘9 be produced at a 
temperature of about — 16°C., the condensation, instead of taking place on a small 
number of scattered nuclei, as with a smaller degree of supersaturation, takes place 
upon a very large number, the number of nuclei which come into play increasing at 
a very rapid rate with increasing expansion. It will be noticed th.at the super¬ 
saturation required to produce either kind of condensation is practically the same in 
all gases, the rain-like condensation, however, being absent in hydrogen. 
2 Q 
MDCC'CXCVII.—A. 
