Condensation, and on the contrast of Colors. 87 



lieat of air is "237, for the given values of temperature about 

 5*17 cal. are absorbed per gram in the adiabatic expansion of 

 dry air. The available calories due to condensation will thus 

 heat this gram 1*77°, which is the correction to be added to f . 



If the above equation for x' is now again used with the new 

 data, 1 — x' — '04:6 grams of water are found for each gram of 

 vapor. Thus 790/ 10 9 grams of water are precipitated per 

 cubic centimeter of moist air under the conditions selected in 

 the experiment. 



I may note in passing that if 5 X 10 4 nuclei are present in 

 the saturated emanation (as found in preceding papers), 16/10 12 

 is the volume of each water particle or about 2*5/10 4cm , its 

 diameter initially. This agrees very well with the results 

 obtained from the coronas below, § 10. 



To find JV for Table I, the equation JV = 10* < I+M > lo *> is 

 given by experiment, where y is the ratio of densities before 

 and after exhaustion. Hence, since initially, = 293°, jp = 76 cm , 

 and finally, 0' = 273°, y = 58 cm , y =-819. Inserting the above 

 value of t and reducing N —10~' lo ° 7n . With these constants 

 the values JV of Table I were computed. 



6. Relative size of particles. — Assuming that the same amount 

 of vapor is condensed per cub. cm. in each expansion between 

 fixed pressures of the moist air in the receiver, the relative size 

 of the particles may be computed for the given orders of coronas. 

 If the size of the particle in any one case were known, all 

 would be found absolutely. It is only after about twenty 

 exhaustions that the ordinary normal coronas are encountered. 

 Table I (last column) contains an example of typical cases. It 

 shows that there is not a striking variation of diameters to cor- 

 respond with the startling variation of coronas. These are 

 thus a rather sensitive criterion of change of diameter of water 

 particles. 



Axial colors. 



7. Conical drums. — It w*ill next be necessary to devise appa- 

 ratus to show greater intensity of axial color (the colors of the 

 steam jet or color tube), with the necessary relation to the 

 coronas. This was originally attempted with tubular appa- 

 ratus ; but in the interest of homogeneity wide conical appa- 

 ratus was finally devised, either a single or a double conical 

 drum subserving the purpose. Effective convection currents 

 are then continually in action within, and the density of distri- 

 bution is uniform, slow work presupposed. With the double 

 drum (apices outward) not only can greater length of column 

 be secured but small end windows of glass suffice. This instru- 

 ment is thus less troublesome than the single drum, the broad 

 glass base of which, even if thick, is liable to break explosively 



