56 



KNOWLE DGE. 



[March, 1902. 



Unlikt' that of tlie piginy flyiug-squinvls, tlic tail of tlicsc 

 rodents is cylindrical and coni]Minitivt;ly thin, vvliili", as 

 already said, the parachute is fully dcvdcipcd between tln' 

 hind legs. 



In the last and finest representative of all the tiyiiiK- 

 squirrels — the species shown on the left side of the accom- 

 panying plate — the writer has a special personal interest. 

 About the year 1878, when in Sriuagar, Kashmir, he 

 purchased the skin of a large flying-squirrel from a 

 rhamra- walla (tanner), who stated that it came from 

 Aster or Gilgit, and that he had never previously seen its 

 like. In due course this skin was brought to England, 

 and converted into a perambulator-rug, in which cajiacity 

 it was in use for several years, on one occasion narrowly 

 esca])ing complete destruction by the jaws of a favourite 

 ]iug-dog. At this period, it may be mentioned that the 

 writer was less well acquainted with mammals, so far as 

 their exteriors are concerned, than he is at the present 

 day. And although he had a suspicion that the skin in 

 question was ])eculiar, no steps were taken to ascertain 

 whether this was really the case. One day, however, in 

 1888, when paying a visit to the Natural History Museum,he 

 was shown a living flying-squirrel from Astor, remarkable 

 for its dark colour and bushy tail, which was pronounced 

 to rejiresent a then unknown species. A brief inspection 

 was suflicient to render it evident that the skin serving as 

 a perambulator-rug belonged to the same species as the 

 living animal, although a much larger and finer individual. 

 It was soon after presented to the Museum, and described, 

 in conjunction with the complete specimen, not only as 

 the type of a new species, but of a new genus, under the 

 title of £upefaurus cinereus. Owing to the splendid 

 development of the tail in the flat skin, the figure of which 

 a reproduction is given on the left side of the accompanying 

 plate wa;S partly drawn from that specimen. 



The main reason for making the woolly flying-squirrel 

 (as, from the nature of its coat, it has been called) the 

 tyi)e of a genvis by itself is afforded by the characters of 

 its cheek-teeth, which differ from those of other members 

 of the grovip by their tall crowns and imperfectly developed 

 roots. This character indicates greater specialisation than 

 the ordinary flying-squirrels. Unfortunately little or 

 nothing is known as to the life-history of this splendid 

 representative of the flying-squirrels, but there is some 

 reason to believe that it dwells, at least to a certain extent, 

 among rocks, rather than in trees. 



Although they do not properly come within the scoi)e 

 of the present article, a few words may be said with regard 

 to the flying-phalangers (the flying-squirrels of the 

 colonists) of Australia, since in one respect they present 

 a curious analogy with the flying-squirrels of the Old 

 World. It need hardly be said that these Australian 

 flying-jjhalangers are true marsupials, with a dentition 

 resembling that of the ordinary phalangers, or, as thev 

 are locally called, opossums. The larger flying-phalangers, 

 which constitute the genus Petaurus, are characterized by 

 the full development of the parachute and the rounded 

 bushy tail. As in the case of the Asiatic flying-squirrels, 

 we are unable to point out the non-volant type of 

 phalangcr from which they are descended. 



On the other hand, the beautiful pigmy flying-phalanger 

 (AcrohntfiH), which differs from the larger forms by the 

 scantier development of its parachute, as well as by its 

 tail being formed after the type of a feather — that is to 

 say being flattened, with a line of hair along each edge — 

 is evidently descended from the non-flying feather- tailed 

 phalangcr (Bistcechurm), or the immediate ancestor of the 

 latter. In this case, therefore, we have an exact parallelism 

 to the descent of the flying representatives of the scale- 

 tails from the non-flying Zenherella. 



THE LUCID STARS. 



By J. E. GOKE, F.K.A.S. 



The term " hicid " has been applied to the stars visible to 

 the naked eye, without optical aid of any kind.* Many 

 peoph- think that the number of stars visible in this way 

 is very large. But in reality the number visible to the 

 naked eye is comparatively small. Some ])ersons are, of 

 course, gifted with very keen eyesight — " miraculous 

 vision" it is sometimes called— and can see more stars 

 than others ; but to average eyesight the number visible in 

 this way, and which can be individually counted, is very 

 limited. The famous Hipparchus formed a catalogue of 

 stars in the year 127 n.c. This presumably contained all 

 the most conspicuous stars he could see in his latitude, 

 and it includes only 1025 stars. Al-Sufi, the Persian 

 astronomer, in his " Description of the Fixed Stars," 

 written in the tenth century, describes the positions of 

 only 1018 stars, although he refers to a number of other 

 faint stars, of which he does not record the exact places. 

 Pliny thought that about 1600 stars were visible in the 

 sky of Europe. 



In modern times, however, a considerable number of 

 fainter stars have been recorded as visible to the naked 

 eye. The famous German astronomer, Heis, who had keen 

 eyesight, records the positions of 3903 stars north of the 

 Equator, and 1040 between the Equator and 20 degrees 

 south declination, or a total of 4943 stars between the 

 North Pole and 20 degrees south of the Equator. This 

 would, I find, give a total of about 7366 stars for both 

 hemispheres if the stars were equally distributed. Behr- 

 mann, in his Atlas of Southern Stars, between 20 degrees 

 south declination and thi; South Pole, shows 2344 stars as 

 visible to the naked eye. This would give a total of 7124 

 for both hemisjdieres. The actual number seen by Heis 

 and Behrmann in both hemispheres is 4943 + 2344, or 

 7287 stars. The Belgian astronomer, Houzeau, published 

 a catalogue and atlas of the stars in both hemispheres, 

 made from his own observations in Jamaica and South 

 America, and finds a total of 5719 stars in the whole sky. 

 As all these observers had good eyesight, we may take a 

 mean of the above results as the total number visible to 

 the naked eye in the whole star sphere. This gives 6874 

 stars, or in round numbers we may say that there are 

 about 7000 stars visible to average eyesight in both hemi- 

 spheres. This gives, of course, about 3.500 stars to one 

 observer at the same time at any point on the earth's 

 surface. 



As the whole star sphere contains an area of 41,253 

 square degrees, we have an average of one star to six 

 square degrees. In other words there is, on an acerage, one 

 lucid star in a space equal to about thirty times the area 

 covered by the full moon ! This result may seem rather 

 sui'prising considering the ajiparently large number of 

 stai-s visible to the naked eye on a clear night, but the 

 fact cannot be denied. The stars are not, of course, 

 equally distributed over the surface of the sky, but are 

 gathered together in some places, and sparsely scattered 

 in others, and this may perhaps help to give the impres- 

 sion of a greater number than there really are. 



That the stars are of various degrees of brightness was 

 recognised by the ancient astronomers. Ptolemy divided 

 them into six classes, the brightest being called first 

 magnitude, those considerably fainter the second, those 

 much fainter still the third, down to the sixth magnitude, 

 which were supposed to be the faintest just visible to the 

 naked eye on a clear moonless night. Ptolemy only 

 recorded whole magnitudes, but Al-Sufi, in the tenth 



Except concave spectacles used by short-sighted persons. 



