138 ANNUAL OF SCIENTIFIC DISCOVERY. 



world abounding in images of almost inconceivable beauty ; but 

 it is very probable that they have more than an ajsthctie value. 

 Tiie assistants who watched the phenomena with the professor, 

 and whose minds were probably of a more practical cast, re- 

 marked that these reactions " would prove exceedingly valuable 

 to pattern-designers ; " and if artistic; skill can seize tliese lleeting 

 phantoms there is no reason why this idea should not be carried 

 out. 



The chemical reactions which occur in these experiments are 

 only slightly noticed, and do not admit of a popular explanation ; 

 it is, however, in the highest degree probable that future chemists 

 will make this form of experiment a potent auxiliary to the labora- 

 tory, while future meteorologists will find in it the true explana- 

 tion of various atmospheric phenomena which as yet remain in 

 more or less obscurity. 



THE BLUE COLOR OF THE SKY, ETC. BY PROF. TYNDALL. 



The idea that the color of tiie sky is due to the action of finely 

 divided matter, rendering the atmospliere a turbid medium 

 through which we look at the darkness of space, dates as far 

 back as Leonardo da Vinci. Kewton conceived the color to be 

 due to exceedingly small water particles acting as thin plates. 

 Goethe's experiments in connection with this subject are well 

 known and exceedingl}^ instructive. One very striking observa- 

 tion of Goethe's referred to what is technically calleil " chill" by 

 painters, which is due, no doubt, to extremely fine varnish parti- 

 cles interposed between the eye and a dark background. Clau- 

 sius, in two very able memoirs, endeavored to connect the colors 

 of tlie sky with suspended water-vesicles, and to show that the 

 important observations of Forbes on condensing steam could 

 also be thus accounted for. Helmholtz has ascribed the blueness 

 of the eyes to the action of suspended particles. In an article 

 written nearly 9 years ago by myself, the colors of the })eat 

 smoke of the cabins of Killarney and tlie colors of the sky were 

 referred to one and the same cause, while a chapter of the 

 •* Glaciers of the Alps," pul/lished in 18G0, is also di'voted to this 

 question. Roscoe, in connection with his truly l)('autiful experi- 

 ments on the photographic power of sky-light, has also given 

 various instances of the production of color 1^}' suspended parti- 

 cles. 



In his experiments on fluorescence, Prof. Stokes had continu- 

 ally to separate the light reflected from the motes suspendetl in 

 his li(iuids, the action of which he named "false dispersion,' 

 from the fluorescent light of the same liquids, which lie ascribed 

 to " true dispersion." In fact, it is hardly possible to obtain a 

 liquid without motes, which j)olarize b}- reflection the light falling 

 upon them, truly dispersed light being nnpolaiized. At p. oiJU, 

 of his celebrated memoir, " On the Change of the Refrangibiiity 

 of' Light," Prof. Stokes adduces some significant facts, and 

 makes some noteworthy remarks, which bear upon our present 



