NA TURE 



[December io, 1908 



In the type of motion which is consistent with a constant 

 value of the energy the velocity of an electron belonging 

 to the ring is directly proportional to the radius of its 

 sphere of interference ; this corresponds to a uniform 

 motion in the symmetrical configuration, and may be 

 derived from it by a conformal transformation. The 

 assumptions made with regard to the mass of an electron 

 and the interference of radiations at the nodes may be 

 justified if the velocity of light within a sphere of inter- 

 ference is directly proportional to the radius. 



The combination of a positive and negative ion may be 

 pictured by supposing that the e.xtra sphere belonging to 

 the negative ion partly fits into the gap in the positive ion 

 in such a way that it is in contact with two spheres belong- 

 ing to the ring in the positive ion, and the atomic spheres 

 of the two atoms are in contact. This would give three 

 additional geometrical conditions. It should be noticed 

 that the electrons would be nearer together close to the 

 point of contact, so that the greater part of the mass 

 would be concentrated round this point. 



The connection between the number of degrees of freedom 

 and valency is discussed in a paper which will appear 

 shortly in the Memoirs of the Manchester Literary and 

 Philosophical Society. Harry Batemax. 



The University, Manchester. 



Silk-producing Insects of West Africa. 



The following observations in connection with the wild 

 silk-producing insects of West .\frica may be considered 

 of interest. In parts of Nigeria (Ibadan, Ilorin, &c.) the 

 cocoons of Anaphe iiifracta, Wlsm., and A. venaJa, Butler, 

 are used for the production of a cloth termed " Sanyan, " 

 which is woven from yarn, spun from the boiled cocoon 

 masses, mixed with native cotton yarns. In a state of 

 nature the silk from the cocoons of both these species 

 is brown or yellow-brown, and is of this colour when 

 exposed for sale in the markets, but another kind of 

 silk, which is brought to Ibadan from Bauchi and Bornu 

 (in N. Nigeria), is pure white in colour, and is called 

 "Gambari," or Haussa silk. This is only obtainable as 

 boiled cocoon masses, and the dried remains of the worms 

 found in them seem to indicate that they are allied to 

 .'\naphe. The collectors of this silk are said to gather 

 the worms from the trees, on which they find them, when 

 Ihey are prepared to spin, and to confine them in 

 calabashes. 



Experimenting with live worms of A. infracta, received 

 from S. Nigeria, I found thai, by confining them in the 

 dark, they produced pure white cocoons instead of brown, 

 although the original larval cocoon was of the latter 

 colour. It seems probable that the " Gambari " silk is 

 white by reason of the confinement of the worms in cala- 

 bashes, as no Anaphe or allied species is known to give a 

 white cocoon naturally. A similar result has been obtained 

 by Lepper in the case of Attacus ricini (the " Eri " silk- 

 worm of India). 



The pupae of A. infracta and .4. venata are eaten as a 

 delicacy by the people of S. Nigeria. Both species seem 

 almost omnivorous in the larva si age, but the first is said 

 to feed, by preference, upon Albizzia jastigiaia and a 

 .Sterculia sp. 



.4. Maloiieyi and A. suhsordida., the first of which has 

 apparently a cocoon mass without an envelope, should, I 

 think, be placed in another genus, by reason of the absence 

 from their forewings of the lower radial vein (No. 5). 



Gerald C. Dudgeon. 



Imperial Institute, November 17. 



Vitality of Leaves. 



I HAVE in my possession a sprig of Bryophylluni 

 calycinum which was cut off a plant in Jamaica six months 

 ago, at the beginning of June. It has still attached to it 

 three leaves, which, are quite green, and at the edges of 

 these there are minute new shoots projecting from the 

 crenations. Only a fortnight ago a leaf plucked from it 

 showed its vitality by giving rise to a new shoot when 

 placed on some soil in a pot. This shoot is growing well 

 under a glass in a warm room. During all these months 

 this small sprig has been lying about in different rooms, 

 without any supply of soil or moisture. 



NO. 2041, VOL. 79] 



Could any of your botanical readers inform me if this 

 degree of vitality, in a detached portion of a plant, is 

 unusual ? Walter Kidd. 



December 7. 



The Exhibition of Fishes in Museums. 



There are at least four museums in the United States 

 in which collections of fishes are exhibited " in which the 

 specimens are presented without the usual iron supports, 

 with sufficient space around each fish and in natural 

 colours " (Nature, October 29, vol. Ixxviii., p. 659). 

 These institutions are the Field Museum of Natural 

 History, Chicago ; Museum of Comparative Zoology, Cam- 

 bridge ; American Museum of Natural History, New York, 

 and Museum of the Brooklyn Institute. 



Furthermore, the last-named museum has an attractive 

 group of fishes of a coral reef amid their natural surround- 

 ings, and the Field Museum has two groups of fresh- 

 water game fishes. F. A. Lucas. 



Museum of the Brooklyn Institute, Eastern Parkway, 

 Brooklyn, N.Y. 



An Electromagnetic Problem. 



The electromagnetic problem enunciated by Prof. Com- 

 stock in Nature of November 19 admits of being solved 

 without any reference to the corpuscular nature of elec- 

 tricity and without going beyond the basis of Maxwell's 

 theory. 



If a be the surface density of the sphere, r its radius at 

 any time, the value of the vector potential at a distance 

 R is ^Tr(rfr'R-'(.ic, y, s). 



Making use of Maxwell's first expression for kinetic 

 energy, ^(Kii — Gt' + Hiw), we get for the kinetic energy 

 J(4iro-r^)'r^r-', from which the problem can be completed. 

 To understand the question fully we must use the retarded 

 formula; for the potentials. Maxwell's expression being only 

 the first terms of expansions in descending powers of C, 

 the velocity of radiation. W'e get in this way more com- 

 plicated values of the potentials, giving, however, no mag- 

 netic force and the original symmetrical electric force. 



The question is interesting as supporting Macdonald's 

 view as to the expression for the energy. It also seems 

 to point out that in any aether theory the vector potential 

 must be looked upon as something more than a mathe- 

 matical abstraction. Arthur W. Conway. 



Cosy Nook, 100 Leinster Road, Rathmines, 

 December i. 



Mercury Bubbles. 



I HAVE often observed these bubbles when purifying 

 mercury. They may be produced very easily by shaking 

 mercury and any liquid in a wide stoppered test-tube, and 

 then suddenly bringing the tube to rest, when the bubbles 

 (of varying size) will be formed. 



I have tried the following liquids : — water, alcohol, 

 ether, acetone, ethyl acetate, acetoacetic ester, amyl nitrite, 

 amyl alcohol, amyl acetate, carbon tetrachloride, benzene, 

 toluene, xyleni-, gelatin, glycerin, formic acid, acetic 

 acid, aniline, carbon bisulphide, toluidine, pyridine, ethyi 

 iodide, methyl bromide, ethyl bromide, methyl iodide, 

 dichloroethylene, ethylene dibromide, chloroform ; it seems 

 that the more volatile and less viscous the liquid, the 

 smaller are the bubbles and the quicker do they burst. 

 Philip Bi.ackman. 



Hackney Technical Institute, N.E. 



In view of the several letters about mercury bubbles 

 which you have recently published, I beg to mention that 

 molten steel is also capable of forming bubbles. If a 

 bucket full of water be placed in a suitable position under- 

 neath and a little to the front of a Bessemer converter, 

 then on removing the bucket after the completion of a 

 blow it will be found to contain small spheres of steel 

 ranging in size from a pin's head to that of peas, and 

 even larger. These spheres are hollow, and some are per- 

 forated, and occasional ones are twins -and triplets, sets 

 of hollow spheres having plunged into the water at the 

 instant thev stuck together. 



West Didsburv. C. E. Stromeyer. 



