176 



SCIENCE. 



[N. S. Vol. XY. No. 370. 



white ligM diverging from an external 

 point. In this way not only were copious 

 fogs obtained, but the coronas* produced 

 were additionally available as evidence. 



In the benzine jet, particles are probably 

 cooled too suddenly, and at once attain a 

 size incompatible with axial color effects. 

 Using the exhaustion method, however, 

 these axial colors appearing in benzine are 

 not only of pronotmced depth, but they run 

 into higher orders than in the case of 

 moist air subjected to like exhaustions. 

 Sequences passing through blue, green, 

 yellow, broAvn, purple, etc., green, brown, 

 etc., may be seen in the axis of a column 

 only 23 cm. long. The reason, no doubt, 

 is the lower latent heat of benzine, insuring 

 the formation of drops not less uniform, 

 but of a size, cset. par., regularly larger 

 than for water vapor. The fact that axial 

 colors are producible both with water and 

 with a pronounced insulator like benzine, 

 is a result of fundamental importance in its 

 bearing on any theory adduced to account 

 for the axial absorption in question. 



3. The exhaustion experiments were thus 

 at once successful. Cloudy condensation 

 was as densely produced in benzine vapor 

 as in water vapor, mth phosphorus, flame 

 and other nuclei. Care was taken to in- 

 sure dryness of vessel by test experiments 

 both before the benzine was introduced and 

 after it had been quite removed by evapo- 

 ration. The exhaustion of about one sixth, 

 say 13 cm., seemed best adapted to bring 



* For some time I have been making experi- 

 ments with the coronas of cloudy condensation on 

 a large scale, with the purpose of comparing the 

 diffraction colors so produced with the axial 

 colors of the steam jet. The latter are almost 

 complementary to the colors of the central 

 patches of the corresponding coronas, betraying a 

 difference of origin in the two cases of great 

 theoretical interest. One is tempted to infer that 

 the light axially absorbed illuminates the colored 

 inner circle of the corona, but the proof of such 

 an assertion is a long stride. 



out the following phenomena. "When the 

 receiver was left standing overnight no 

 marked condensation occurred in the ab- 

 sence of nucleation, or else the condensa- 

 tion was rain, like a fine mist, falling about 

 2 or 3 em. per second. 



The introductory experiments were made 

 with light nearly in parallel, the sun's 

 image being used as a coronal center. The 

 even dense tawny benzine fog after the first 

 nucleation was expected to develop on 

 subsequent exhaustions (each followed by 

 an influx of filtered air) into the magnifi- 

 cent coronas which characterize this ex- 

 periment in the case of water vapor. On 

 the contrary, however, the fogs were more 

 fleeting, showed a more rapid descent than 

 aqueous fogs, and the color fields obtained 

 were not ring-shaped as expected, but 

 sharply stratified, horizontally, roughly 

 speaking, in alternations of green and red. 



Moreover, if the exhaustions were made 

 successive without influx of air between 

 each, the colors rose in strata from below, 

 as they fell in strata when left to them- 

 selves. On mounting, the strata grew suc- 

 cessively wider and thinner till they van- 

 ished from sight, brown, yellow-white being 

 the last colors observed. Uniform color 

 fields (strata of limiting width) were 

 eventually producible in this way. Tellow, 

 brown, crimson, arose from a whitish blue 

 base, then descended again on completed 

 exhaustion, reminding one of the extension 

 of an accordion. The speed of apparent 

 viscous subsidence of the top bands has no 

 direct meaning, since fall (or rise) is here 

 complicated by evaporation. 



On entrance of air, vortices were evi- 

 denced by ring-shaped threads of color so 

 that mixture was at first inevitable. One 

 must wait till this ceases before again ex- 

 hausting. Convection currents due to local 

 reheating of the adiabatically cooled gas by 

 the walls of the receiver, were equally 

 apparent, stringy colors rising on the out- 



