108 FKAGMENTS OF SCIENCE. 



commotions were most intense; here buds of cloud 

 would sprout forth, and grow in a few seconds into per- 

 fect flower-like forms. The cloud of iodide of isopropyl 

 had a character of its own, and differed materially from 

 all others that I had seen. A gorgeous mauve colour was 

 observed in the last twelve inches of the tube; the va- 

 pour of iodine was present, and it may have been the 

 sky-blue scattered by the precipitated particles which, 

 mingling with the purple of the iodine, produced the 

 mauve. As in all other cases here adduced, the effects 

 were proved to be due to the light; they never occurred 

 in darkness. 



The forms assumed by some of those actinic clouds, 

 as I propose to call them, in consequence of rotations 

 and other motions, due to differences of temperature, 

 are perfectly astounding. I content myself here with a 

 meagre description of one more of them. 



The tube being filled with the sensitive mixture, the 

 beam was sent through it, the lens at the same time 

 being so placed as to produce a cone of very intense 

 light. Two minutes elapsed before anything was vis- 

 ible; but at the end of this time a faint bluish cloud 

 appeared to hang itself on the most concentrated por- 

 tion of the beam. 



Soon afterwards a second cloud was formed five 

 inches farther down the experimental tube. Both 

 clouds were united by a slender cord of the same bluish 

 tint as themselves. 



As the action of the light continued, the first cloud 

 gradually resolved itself into a series of parallel disks of 

 exquisite delicacy, which rotated round an axis perpen- 

 dicular to their surfaces, and finally blended to a screw 

 surface with an inclined generatrix. This gradually 

 changed into a filmy funnel, from the narrow end of 

 which the ' cord ' extended to the cloud in advance. 



