November 1, 1895.] 



KNOWLEDGE. 



255 



possible changes, it appears to me that there is another 

 means Dr. Eoberts has omitted to notice, which would be 

 easily applied to the whole cluster at a glance. If the two 

 pictures are mounted as a stereoscopic slide and viewed in 

 the stereoscope, any stars which have moved sufficiently 

 will stand out from the picture plane or appear to recede 

 behind it, and a very small motion will be thus easily 

 detected. I do not know if any valid objection exists to 

 this proposal, but, if not, it appears to me the most simple, 

 certain, and readily applied of any. 



But there are several preliminary considerations which 

 occur to me upon which Dr. Eoberts could enlighten us. 

 Is it certain that two negative films exposed at intervals of 

 years apart will undergo the same deformations during 

 development and after operations '? Is the coUotype 

 process also reliable to such an extent as to eliminate all 

 danger of accidental displacements '? Is the ordinary 

 photographic print reliable in the same way '? Is the 

 enlarging process quite certain not to produce any change 

 of relative place. And — not least — the stars are not round 

 on these photographs, and there seems a probability that 

 the deformations may not be in the same direction on 

 different negatives. An illusory displacement would result 

 from this. Besides, the enormous photographic discs tend 

 to mask all changes. 



I doubt if any change amounting to one second in eight 

 years is at all likely, but that change is going on is certain, 

 and that Dr. Eoberts' photographs will at some future time 

 lead to its detection there can be no doubt. 



Edwi.v Holmes. 



THK DARK HEMISPHERE OF VEXUS. 

 To the Editor of Knowledge. 



Sir, — During my observations of the planet Venus this 

 summer, I noticed almost invariably, towards the inferior 

 conjunction of the planet with the suu, that its unillumi- 

 nated hemisphere was distinctly visible, and that it was, 

 moreover, darker than the bluish background of the sky 

 itself. 



Now, in trying to find a plausible explanation of this 

 remarkable phenomenon, the idea came to me that the 

 appearance might be due to the fact that in such positions 

 the planet is invariably seen projected on the brightest 

 portion of the solar atmosphere, or rather luminous matter 

 surrounding the sun, which, as the zodiacal light teaches 

 us, extends to a very great distance from that luminary. 



It is evident that in such a case the dark side of Venus 

 ought to present the appearance actually observed — that of 

 a dusky (violetish) globe, projected on a sHghtly more 

 luminous background. For even in the case of the solar 

 atmosphere, or luminous envelope, extending farther than 

 the earth's orbit (as the gegenschein would tend to show), 

 the appearances would not be sensibly altered, as the 

 planet would then be seen through the more rarefied 

 portion of the great solar envelope, whilst it would have 

 behind it, or the part on which it would be projected, the 

 brightest and most condensed portion of the same envelope. 



The darkness of the unilluminated hemisphere of Venus 

 could hardly be satisfactorily explained otherwise. It could 

 not, of course, be due to phosphorescence, because phos- 

 phorescence means light, and light, however feeble, cannot 

 be darker than space itself. E. M. Axtoxlu)!. 



Constantinople. 



— I * I 



HAIR3 oy BEES' MANDIBLES. 



To the Editor of Knowledge, 



Sir, — My attention has just been drawn to a letter on 

 page 235, by Mr. W. Wesche, headed " Hooked Process on 



Bees' Mandibles.' There is a row of hairs on the inner 

 surface of a worker's jaw, situated along the side of a 

 ridge or keel, and he will find them mentioned and illus- 

 trated in Cowan's '■ The Honey Bee, its Natural History, 

 Anatomy, and Physiology," which is the standard text 

 book used in the examinitions for certificates granted by 

 the British Bee-keepers' Association. This is a much 

 more recent work than Cheshire's " Bees and Bee-keeping." 

 Also Schiemenz, in his " Ueber das herkommen des Fatter- 

 saftea," mentions and also gives a very accurate illustration 

 of them. 



The function of these delicate hairs is to assist in 

 mastication, and they come into operation when the saliva, 

 produced by the gland, known as System IV., in connection 

 with the mandible, is poured out while chewing pollen and 

 kneading wax. They entirely differ in shape from the 

 wing-hooks, and are not twisted like these. They are not 

 used for clustering as suggested. In clustering, bees hang 

 on by their claws, those of the hinder legs of the bee above 

 being hooked into the claws of the forelegs of the one 

 below. The hooks on the smaller wing do not give the 

 name to the Hymenoptera. This name is derived from 

 i(x);r, a membrane, and T^zspov, a wing, meaning mem- 

 branous winged. Thos. Wji. Cowan. 



31, Belsize Park Gardens, 



Hampstead, N.W. 



THE PUZZLE OF 



'26.' 



To the Editor of Knowledge. 



Sir, — I have just received from Mr. T. Ordish, 99, Fore 

 Street, one of his " puzzle of 26," and as it is quite equal 

 to any magic square in the curiousness and harmony of 

 its results, I send you some details which will interest 

 your readers. The discovery is quite new, I believe. It 

 consists of two equiliteral triangles intersecting each other 



(Xatural arrangement of Figures.) 



PsoBLEM. — Place the numbers 1 — 12 along the sides of tno 

 equilateral triangles interlaced so that thev shall add up 26 on eaeU 

 of the six sides, and so that the six numbers round the centre and 

 adjacent thereto shall also make 26. 



(as shown above in the "Natural Hexagon ' where the 

 numbers 1 — 12 are arranged in their natural sequence). 

 When arranged thus it forms what might be called the 

 Hexagon, or " Star " of 13. All its diameters, diagonals, 3 

 great and 3 lesser, sum that number, and the inner and 

 outer circles sum three times 13, or 39. But this is my 

 own idea. Mr. Ordish's puzzle of 26 differs in this, that the 

 numbers 1 — 12 are arranged so as to sum 26 in :30 

 different ways, viz., 1 hexagon, 2 triangles, 6 sides, 6 acute 

 angles, 6 obtuse angles, 3 rhombs, i rhomboids, and there 

 may be other ways. The outer circle or hexagon sums 

 52, or double the inner. Perhaps your readers will give 

 the result of their investigations in your next issue, for I 

 believe there are at least six ways of setting the numbers so 



