34° 



SCIENCE-GOSSIP. 



are altogether perplexing. Let us look to some of 

 the facts to which they call attention. Long ago 

 Schroter — whose telescopes included a nineteen- 

 inch reflector — and Gruithuisen believed that they 

 detected traces of a faint twilight extending beyond 

 the cusps. The Rev. T. "W. Webb and others have 

 suspected something of the same sort, and twenty 

 years since, the brothers Henry, with the large 

 refractor of the Paris Observatory, observed faint 

 but decided traces of this appearance. Further, 

 at Arequipa the same thing has been observed 

 frequently. Such observations, however, need the 

 very finest conditions of our own atmosphere. 



Sometimes a peculiar phenomenon known as 

 projection is observed at the occultation of stars : 

 this has been supposed by some to be due to the 

 refraction of a lunar atmosphere, the star being 

 apparently projected on to the disc of the moon. 

 Simultaneous observations, however, seem to force 

 the conclusion that the effect is an illusion pro- 

 bably produced by an error in focussing ; the 

 real error lying in the eye itself being affected by 

 the different brilliancy of the star and moon, in the 

 same way that, when observing the sun, a telescope 

 exactly focussed on the limb will be found to 

 require a slight readjustment if turned to an object 

 in the centre of the disc. 



Writing of occultations, however, reminds me of 

 those of planets occasionally observed. In 1857, 

 August 7th, 1889, and June 14th, 1896, during the 

 progress of the occultation, a narrow dark band 

 was observed on the planet at the edge of the 

 moon's limb. Were the observations only visual, 

 some doubt might be thrown upon them. In the 

 later occultation, photographs were taken — particu- 

 lars of which will be found in Vol. xxxii. Part 1 of 

 " Annals of the Harvard Observatory " — which not 

 only showed the dark band, but also, both before 

 disappearance and after reappearance, showed a 

 halo around the planet's disc. Professor Pickering 

 has kindly written to say that " it is impossible to 

 show the dark band on Jupiter on paper satisfac- 

 torily, though it is well seen in the negative." 

 Another remarkable thing was noticed, both 

 visually and in the photographs, at the occultation 

 of the same planet, August 13th, 1892 : Professor 

 Pickering found a slight but decided flattening of 

 the planet's limb as it approached the moon ; the 

 distortion did not exceed i", therefore he considers 

 the actual density of a lunar atmosphere must be 

 very slight — not exceeding Tro 1 ^ part that of our own. 



Both Hahn and Gruithuisen saw faint nebulous 

 streaks of light within the dark side of the moon 

 close to the terminator or boundary between the 

 enlightened portion and the shadow, which the 

 latter believed to be hazy clouds. Schmidt, April 

 25th, 1S44, saw just such a glimmering patch, of a 

 bluish colour, to the south-east of Pice, in a position 

 where no mountain peak exists, as this lofty peak 



was disappearing beyond the terminator. Madler 

 had seen something similar within lofty ring-plains. 

 In 1871 three observers in different parts of 

 England noticed a similar phenomenon within 

 the ring Plato on the north border of the Mare 

 Imbrium. Schmidt was convinced that what he 

 saw was not a telescopic "ghost," nor caused by 

 the secondary spectrum. 



Another phenomenon has been frequently met 

 with by persistent workers : portions of the disc 

 have become "fogged," so that it has been 

 impossible to "get at" the details, whilst the rest 

 of the disc has been crisp and sharp. This has 

 been observed in the Mare Serenitatis. In the ring 

 Plato, some sixty miles in diameter, Bert and others 

 noticed phenomena in connection with the visibility 

 of craterlets, light specks and streaks on the floor, 

 which seem only explicable by accepting the 

 presence of an atmosphere. Similar observations 

 have latterly been made at Arequipa in Peru, 

 where the Harvard observatory has a branch 

 establishment, the atmospheric conditions being of 

 the best. A singular phenomenon is noticed about 

 this crater — that the longer it is exposed to the 

 sun's rays as they rise upon it, the darker the 

 floor becomes. 



The Mare Crisium is subject to peculiar changes : 

 " On rare occasions it has been seen by Schroter, 

 and in part by Beer and Madler, speckled with 

 minute dots and streaks of light. Something of 

 this kind I saw with a fluid achromatic, July 4th, 

 1832, near I. Quarter. A similar appearance 

 was noticed by Slack, and Ingall, 1865 " (-). Mr. 

 Slack says that the delicate bands of light radiated 

 " from the vicinity of a small mountain near 

 Picard, Several light spots were also noticed 

 in parts of the same sea which are usually 

 dark." The reason that these objects are so 

 seldom visible seems impossible of explanation, 

 unless the presence of an atmosphere be ad- 

 mitted. Another phenomenon has been noticed by 

 the writer upon the surface of this Mare, A little 

 outside its eastern border there is a brilliant crater 

 called Proclus. from the brilliance around which 

 a number of bright streaks radiate ; there being 

 apparently four centres of radiation. Some of these 

 streaks extend a considerable way across the Mare. 

 One of the shorter of the streaks, radiating from a 

 point just off the south-west wall of Proclus, passing 

 a little to the north of Picard, is not always in the 

 same position with regard to a small crater on the 

 Mare known as Picard E., as if the streak had a 

 motion from north to south. 



A similar motion has been suspected from east 

 to west in the case of the streak from Tycho, which 

 crosses the Mare Serenitatis, and upon which the 

 crater Bcssel is situated. 



( 2 ) "Celestial Objects for Common Telescopes," by Rev. 

 T. \V. Webb. Third Edition, p. 82. 



