These instances of course cannot be connected with the Aurora except as showing the spectrum region and lines of fluorescence. The sea phosphorescence, according to Professor Piazzi Smyth, has a continuous spectrum extending from somewhat below E to near F (Plate V. fig. 3). [Sidenote: Ångström finds the sky almost phosphorescent.] Ångström, on the occasion of the starry night when he found traces of the green line in all parts of the heavens, speaks of the sky as being “almost phosphorescent.” [Sidenote: Author of article in Encyc. Brit. suggests that the phosphorescent or fluorescent light may be due to chemical action. Herschel’s observation of phosphorescence in Geissler and “garland” tubes.] The author of the Aurora article in the Encyc. Brit. suggests that the phosphorescent or fluorescent light attributed to the Aurora may be due to chemical action. He also questions Ångström’s assumption that water-vapour is absent in the higher atmosphere, and thinks that it and other bodies may, by electric repulsion, be carried above the level they would attain by gravity. He then continues that if discharges take place between the small sensible particles of water or ice in the form of cirri (as Silbermann has shown to be likely) surface decomposition would ensue, and it is highly probable the nascent gases would combine with emission of light. He adds “that it has been almost proved that in the case of hydrogen phosphide the very characteristic spectrum (light?) produced by its combustion is due neither to the elements nor to the products of combustion, but to some peculiar action at the instant of combination; and it is quite possible that under such circumstances as above described water might also give an entirely new spectrum.” Professor Herschel has referred to the phosphorescent light which remains glowing in Geissler tubes after the spark has passed, and to the fact that one of the globes of a “garland” tube which was heated did not shine after the spark had passed, apparently because of the action of heat on the ozone to which the phosphorescence might be due. (See experiments on Mr. Browning’s bulbed tube, Part III. Chap. XV.) _Aurora and Ozone._ [Sidenote: Aurora and Ozone. Smells of sulphur during Auroræ attributed to ozone.] Accounts are given by travellers in Norway of their being enveloped in the Aurora, and perceiving a strong smell of sulphur, which was attributed to the presence of ozone. M. Paul Rollier, the aëronaut, descended on a mountain in Norway 1300 metres high, and saw brilliant rays of the Aurora across a thin mist which glowed with a remarkable light. To his astonishment, an incomprehensible muttering caught his ear; when this ceased he perceived a very strong smell of sulphur, almost suffocating him (‘Arctic Manual,’ p. 726). [Sidenote: Question whether the oxygen of the air may be changed into ozone.]