]5S 



KNOWLEDGE. 



[JnLY, 1902. 



m)t be affocted by this change in the position of the hoii-l 

 if it is not due to that cause. 



It. .7. KylK, M.I). 



15, German Place, ]?i-i<,'htc)u. 



[Mr. E. Sillence (Romscy) writes to say: "1 have no 

 iloubt that twice lu inv life I have seen the crescent of 

 Venus with my naked eye." Mr. Sillcnoe believes that 

 the occasion of these observations was June, 1897, the 

 planet being observed in the bright dawn before sunrise, 

 " so that the usual glare of the planet was gone." The 

 claim that the crescent of Venus has been seen with the 

 naked eye has been made several times, no doubt in the 

 conii)lctest good faith. But since — as Dr. Eyle is without 

 doubt right in suggesting — the impression has often been 

 due to astigmatism of the eye, and as in other cases 

 imagination may have been at work, it is essential that 

 before any such claims can be accepted as a scientific fact, 

 the observer should have not only been careful to put on 

 record the exact time and conditions of his observation, 

 but should have been able to show by many experiments, 

 in which the influences of astigmatism and imagination 

 were excluded, that he really possessed the ocular ability 

 necessary to perform so astonishing a feat. — E. Walteib 

 Maunder.] 



THE DATE OF STONEHENGE. 



TO THE EDITORS OF KNOWLEDGE. 



Sirs, — In the May number of Knowledge Mr. Maunder 

 states that the dates which different careful observers 

 have deduced for the erection of Stonehenge extend over 

 a ]ieriod of more than 2000 years. While this statement 

 is true if all the derived dates are included, I think it may 

 be worth while to point out that only two of the attempt^ 

 to determine tlie date astronomically have been made with 

 a proper grasp of the conditions of the problem and with 

 adequate data— one by Prof. Flinders Petrio in 1881, and 

 the other by Sir Norman Lockyer and Mr. Penrose last 

 year. Other determinations may be left out of considera- 

 tion, because usually no allowance has been made for 

 refraction and elevation of the horizon, both of which are, 

 of course, important factors in modifying the apparent 

 direction of sunrise. Prof. Petrie's observations were 

 made differentially with evident care, but the date 730 a.d. 

 which he derived cannot be accepted, for the simjjle reason 

 that in the calculation on which the result is based the 

 variation of the obliquity of the ecliptic was, by a curious 

 slip, applied in the wrong direction. The determination 

 by Sir Norman Lockyer and Mr. Penrose thus practically 

 stands alone, and the date 1680 ± 200 b c. which they 

 deduced is in as close agreement as can be expected with 

 the 2000 B.C. which Dr. Gowland has since derived from a 

 consideration of the objects found in the excavations. 



A. Fowler. 



THE SUN PILLAE OF MARCH 6. 



TO THE EDITORS OF KNOWLEDGE. 



Sirs, — There is one point with regard to the sun pillar 

 which was seen on March (Jth which 1 have seen no notice 

 of anywlK're ; and so I venture to call your attention to 

 it— pi'rha])s without occasion — viz., the large porriou of 

 the country over which it was visible. I cut out letters in 

 the 2'imes showing it was visible at Falmouth, Salisbury, 

 and Cranleigh in Surrey. Also at Woking and Guildford 

 and Crawley, Royston, Oxford, Horsham, Ilindhead, 

 Botley, Bournemouth, and Braunton (North Devon). 

 These are all below the 52ud parallel. I can, however, 

 add about another degree of northing to that, for I saw it 



very plainly from here. This means that it was visible 

 over about half of England at any rate. Is it then some- 

 thing cosmical lut the sun shining upon a ring of innumer- 

 able small bodies in space, and the light being refh-cted to 

 us; or is it due to a condition of atniosi)here extending 

 over hundreds of square miles, and causing each one of us 

 to see his own sun pillar, as he sees his own rainlx)W ? 



Pool Quay, Welshpool. R. J. Roberts. 



[In reply to Mr. Roberts and to other coiTCspondents 

 who have asked for an explanation of the cause of a sun 

 pillar, there can be no doubt that his second alternative is 

 the correct one. A sun pillar is due, not to any cosmical 

 collection of particles outside our own atmosphere, nor to 

 refraction, but to reflection, the n.'flection that is to say of 

 the sun from the under surfaces of ice films floating hori- 

 zontally in still air. The phenomenon therefore bears a 

 close analogy to the very familiar one of the " track " of 

 light which we see upon still water when we are looking 

 across it towards a low sun. As each several observer sees 

 his own " track," so each observer sees his own sun pillar. 

 The two phenomena are shown together in the sketch of 

 the sun pillar of January 30th, 1895, drawn by the Rev. 

 Samuel Barber for Knowledge, June, 1895. — E. Walter 

 Maunder]. 



BKTTJSlf- 



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ORNiTHOLOGlCAl?*^ .=^ 



Jl :J'-.. .-. ": ^ ''^' ''_:KOIESitl 



Conducted by W. P. Pycraft, a.l.s., f.z.s., m.b.o.u. 



Penguin Footprints. — At the meeting of the British 

 Ornithologists' Club, held on the 21st of May, Dr. R. 

 Bowdler Sharpe, ll.d., ■ exhibited some remarkable 

 specimens of rocks Ijrought from the Falkland Islands by 

 Mr. Rupert Vallentin. These rocks formed the track from 

 the landing place to the breeding ground of the Rock- 

 hopjjer Penguin, Catarrluides chrysocome, and consecjuently 

 had been constantly traversed by thousands of birds for 

 countless generations. As a result the surface of the rock 

 had become marked by deej) " scores " made by the claws 

 of the birds as they scrambled over its surface. Many 

 larger slabs of rock, showing still better traces of this 

 restless traffic, were taken, but were lost through ship- 

 wreck on the voyage home. 



The Life-History of the Penguin. — An extremely 

 interesting and valuable account of the life-history of the 

 Emperor and Adelia Penguins will be found in the Report 

 of the Southeru Cross Collections made during Sir George 

 Newues' Antarctic Expedition in 1898. Some of the most 

 interesting of these notes possess a peculiarly mournful 

 interest, having been made by the unfortunate naturalist 

 Nicolai Hansen, who died during the expedition. No less 

 interesting are the notes of Mr. Bernacehi. "By far the 

 the largest Penguin rookery seen during the expedition," 

 he writes, " was that of the Adelia Penguin at the foot of 



