J.TNE, 1902.] 



KNOWLEDGE. 



133 



behiinl it. Nine foet awaj place any iiolislied convex 

 surface, and view the reflected crescent in this at tiftcen 

 times the radius of the surface, or the crescent moon will 

 answer the same purpose as the card crescent. The radius 

 of the reflectinjr convex is not of importance so long as 

 the o))server is fifteen times that radius away. 



RnwiN Holmes. 

 'I thank Mr. Holmes for drawing my attention to the 

 paper to which he refers. I had missed it, as it appeared 

 during my absence in Mauritius. I gave the particulars 

 respecting my own eyesight merely to show that it was 

 not due to any inferiority in it as coinjiared with average 

 sight that I have ahvays failed to define the crescent of 

 Venus. Anyone who has done .so must have sight sei'eral 

 timeit as good as mine ever was. The maximum elonga- 

 tion of Jupiter II. from" the centre of the planet is "almost 

 four minutes of arc " if Jujiiter be in opposition and at 

 perihelion at the same time. Thus its elongation was 

 3' .H" on 1880, October 6.— E. Walter Maunder.] 



THE CSE OF HAND TELESCOPES IN 

 ASTRONOMY. 



TO THE EDITORS OF KNOWLEDGE. 



Sirs, — May I suggest that the remarks respecting 

 Jupiter and Saturn, on page 81, are somewhat misleading. 

 No note is made as to the visibility of details being affected 

 by the declination of the planets. As long ago as IS(il, 

 '■ llei-reative Science" contained (under a, nnin de phiine) 

 some observations of mine made with a H in. telescope. 

 With this the cra]>e ring was often seen where it crosses 

 the ball, while Jupiter's belts could not be overlooked. 

 But in IBtil both planets, especially Jupiter, had con- 

 siderable northern declination. .F. W. Levanuer. 



'M^, North Villas, Camden Scpiare, N,W. 



0"RlTlsit 



^'% 



ORNITHOLOGrCAt 



NOTES. _: 



ConiluHeil hij 'W. V. Ptceaft, a.l.s., f.z.s., m.is.o.u. 



TJiRii Mh;ration.— The Th!i< for April contains a most 

 valuable contribution to this most fascinating study, liy 

 Mr. W. Eagle Clarke, one of our greatest authorities on 

 the subject. Mr. Clarke's observations were made during 

 a month's stay in the famous Eddystone Lighthouse. 

 Deciding that the autumn was the best season for observa- 

 tion, he took up his residence on the 18th September, and 

 left on the Iflth of October, 1001. Cloudless and 

 moonlight nights were singularly unproductive, not 

 because no passage-movements took place but because 

 they were beyond the range of observntion. The 

 most successful nights were those when the atmosphere 

 was saturated with moisture (rain, haze, cloud). This 

 mixture "becomes more or less opaque, while the powerful 



beams, streaming out from the lantern upon it, bec(.)me 

 luminous and lirilliaiit to a very remarkable degree, and 

 exert extraordinary attractive powers over the migrants 

 that pass within their sphere of influence." The main 

 factors in migration movements, Mr. Eagle Clarke 

 points out, are not the winds, but certain svstems 

 of atmospheric pressvn-e which estalilish fine weather- 

 conditions in the N<n-th Sea. The winds are the result of 

 tliese pressure systems, and appealing more to the senses, 

 have come erroneously to be regarded as the principal 

 cause of migratory movements. 



M.ALE Birds in Ekmale Plumage. — The FiehJ, April 

 2(Jth, contains a short but interesting article on this 

 subject by Mr. W. B. Tegetmeier. The author points out 

 that there are breeds of game fowls in which the males 

 habitually wear the female attire, and are known in 

 consequence as ■' hennios." No less fertility or courage 

 follows the change of livery ; on the contrary, " hennies " 

 were remarkable as being the most dangerous birds in the 

 cock-pit. The origin of these hen-feathered biixls, Mr. 

 Tegetmeier attributes " to an accidental variation, of the 

 causes of which, like those of other variations, we know 

 absolutely nothing." 



Rooks with Feathered Faces. — In a letter in the 

 Field, May 3rd, it is suggested that Rooks with feathered 

 faces are becoming more common on account of changed 

 habits, the Rook having largely relinquished its habit of 

 digging for food in favour of egg-stealing. This question 

 has been raised and discussed before. So far the evidence 

 seems to lend little support to this theory, but rather to 

 suggest a reversion to the conditions common to all the 

 members of the family save the Rook. 



Penguins at the Zoological Gardens.— It may interest ouv readers 

 to know that an unusually fine eoUection of tlicse birds can be seen at 

 the Gardens at the present time. The species represented iiielude 

 three King Penguins (Apteiiodyte.i pennantij, the Black-footed 

 Penguin ('Sphenisms demersitsj, Selater's Penguin (Calarrhacles 

 SclateriJ, and the Thick-billed l^enguin (C. pachyrhgnchus), 



Bird-Life in Norway.— Land and Water, April 26th, contains an 

 exceedingly interesting article on bird-life in Xorway. The bulk of 

 this is a translation of a paper by Prof. R. CoUett. Those of us who 

 cannot read Norwegian should be grateful to the translator, for much 

 valuable information has now been made accessible concerning the 

 breeding habits of a number of clilT-haunting species. 



All contributions to the column, either in the way of notes 

 or photographs, should be forwarded to W. P. Pycr.vft, at the 

 Natural History Museum, Cromwell Road, London, SJV. 



Botanical. — An interesting paper on abnormal fruits — a 

 melon in which the seeds had precociously germinated, and 

 an orange, which showed plciotaxy oc the gynaeceum — 

 appeared in the March number of the Annah of Boliniii, 

 contributed by Sir W. T. Thiselton-Dyer. The melon 

 when cut open was found to have its interior filled with 

 well-developed young plants. It was satisfactorily 

 determined that these had not originated from intra- 

 ovarian buds, but from seeds, for in some cases the two 

 halves of the testa were still attached to the cotyledons. 

 The pericarp of the melon, though li inches thick 



