5H 



NA TURE 



[September 27, 1900 



organs. How does it come to pass that in autumn the leaves of 

 some of our forest trees exhibit a brilliant livery of crimson, 

 while others exhibit only a yellow or golden glory ? Take, for 

 instance, the case of the ash constituents in the dry substance of 

 the leaf. It is known by analysis that the percentage of ash 

 increases through nearly the whole life of the leaf in beech, 

 sycamore, elm, but not in oak, larch, cherry, &c. ; it depends a 

 good deal on whether some one ash constituent (generally lime 

 or silica) is being steadily stored up. For example, the dry leaf 

 of Acer campestre on May i has 6 per cent, ash, and in October 

 i6'2 per cent, ash ; the dry leaf of Prunus avitini has on April 

 28, 7*8 per cent., and on October 2, 7*2 per cent. ash. Now the 

 leaf of the former tree is only yellow in autumn and never red, 

 while that of the latter is very often beautifully crimson. In the 

 former case there is a kind of gradual decay or death of some of 

 the cells (mostly of the upper epidermis) which occasions a 

 drainage of mineral and organic substances to these parts from 

 the still living tissues. This drainage and accumulation attest, 

 in fact, such a decay ; and what is more, they seem to have a 

 distinct influence over the ultimate autumnal coloration of the 

 leaf itself. It is easy to understand, in fact, that the leaves 

 which exhibit such a decay and approach to dissolution are just 

 these wherein the chromogen precursive of the brilliant red 

 coloration would likewise suffer an analogous kind of change, 

 i.e. it would tend to become brown, to produce phlobaphene, 

 just as it does in the outer bark which is the practically dead 

 portion of the rind. Where this accumulation of mineral matter 

 and all which it implies does not take place, as in cherries, 

 currants, American oaks, pears, wild vine, barberry, &c., then 

 the chromogen does not deteriorate ; it evolves its proper pig- 

 ment, and assumes the flush and glow of active living colour. 

 On the other hand, in elms, chestnut, linden, birch, poplars, &c., 

 which are never red but only yellow, it is only the vivid carotin 

 attached to the last faded and now exhausted chlorophyll which 

 gleams forth, but only for a time, and if not too much ob- 

 structed by the dull browns of decomposed carbohydrates and 

 superoxidised tannic chromogens. P. Q. Keegan. 



Patterdale, Westmorland. 



Homochronous Heredity and Changes of 

 Pronunciation. 



Seeing that in ancient German, or rather Gothic, Swedish, 

 Danish, probably in French, and possibly in Sardinian, the th 

 sound surviving in English (though much less frequent than it 

 used to be) was once largely used, but nowadays Frenchmen 

 and Germans find a difficulty with it, I should like to know 

 whether systematic experiments have been made as to whether 

 children of various ages of these two nationalities can pronounce 

 it more exactly and spontaneously than their compatriots of a 

 maturer age ? I should like to make the same inquiry concern- 

 ing English children and their pronunciation of the gutturals 

 discarded or altered in such words as night, bough or laugh ? 

 Charles G. Stuart-Menteath. 



23 Upper Bedford Place, W.C. 



Authorities: — Helfenstein, "Comparative Grammar of the 

 Teutonic Languages," 1870, pp. 156-9; G. Koerting, " Neu- 

 griechisch und Romanisch," 1896, p. 23 ; W. Meyer-Luebke, 

 "Grammatik der Romanischen Sprachen," 1890, p. 428. 



The Daylight Meteor of Sunday, September 2. 



As Mr. Denning expresses a wish in your issue of Sep- 

 tember 13 for further information concerning this meteor, I 

 write to inform you of what I saw myself. 



I observed the. time at which the meteor fell, and made it 

 6.50, but my watch is no chronometer. I saw the meteor from 

 the road, between Deganwy and Llandudno, and it appeared 

 to fall over the Little Orme's head. If you joirt this point to 

 Leyburn in Yorkshire, you have the line as near as I can give it, 

 and I do not think it is very far out. I did not note any column 

 of smoke or cloud after the meteor fell. Its path was vertical. 

 Some one says its angle of appearance was 35°, and disappear- 

 ance 25^, which I should say is about correct. Ttie sun was 

 shining brightly, though low down in the west. The brilliance 

 was greatest just before disappearance. I have never before 

 seen any meteor to compare with it in brightness. 



38 Hillfield Road, Hampstead. T. RoOKE. 



NO. 161 3, VOL. 62] 



The meteor of September 2, described in your issue o- 

 September 13, was seen in Ireland also, in even brighter day- 

 light. 



I noted the time, 6.27 p.m. (Irish), and the direction, E.N.E., 

 from a point near Enniskerry, co. Wicklow. There was a 

 possible error of a couple of minutes in my watch, and a con- 

 siderable error possible in the estimated direction, which was 

 a rough approximation made without a compass. 



B. St. G. Lefroy. 



THE THEORY OF IONS. 



"pVER since Faraday enunciated the law of electrolysis, 

 ■*-' that the same quantity of electricity passed when 

 chemically equivalent masses of different substances were 

 produced, it has been a matter of speculation whether 

 this may not be due to atomic charges of electricity. 

 Every one, in describing electrolysis and explaining how 

 the substances evolved appeared at the electrodes with- 

 out any apparent action in between them, based his 

 description and explanation upon the supposition of elec- 

 tric charges on the atoms. Some substances, such as 

 hydrogen, were given positive, and some, such as chlorine, 

 were given negative charges, and the electric current 

 through the liquid was explained as due to the convection 

 of these charges by the moving atoms or groups of atoms, 

 and the movements of these were ascribed to the electric 

 force acting on these charges. The amount of the charge 

 on each atom or group of atoms was proportional to its 

 valency, and as this has with good reason always been 

 taken as a whole number, the charges ascribed to the 

 moving elements were all simple multiples of the charge 

 ascribed to a monovalent atom, such as hydrogen or 

 chlorine. All this has naturally led to the hypothesis 

 that electricity itself is atomic. In electrolysis, at least, 

 there is a certain minimum quantity that corresponds to 

 a single atomic bond, and quantities of electricity trans- 

 ferred by electrolysis are always multiples of this unit. It 

 was surely natural, then, to give a name to this important 

 physical unit quantity of electricity, and it has conse- 

 quently been called an " electron." 



Further, in electrolysis, the electrons always appear 

 connected with, and travelling with, certain atoms or 

 groups of atoms. For example, in copper sulphate solu- 

 tions, the positive electrons travel in pairs with the 

 divalent copper atoms, and the negative electrons with 

 the divalent atomic group SO4. These charged atoms, 

 or groups of atoms, playing such an important part in 

 electrolysis, have been called " ions." 



Now there is a very important difference between 

 different liquids in their behaviour when we try to pass 

 an electric current through them. Some are quite easily 

 decomposed, others offer a very great resistance, and it has 

 been a matter of most interesting speculation as to the 

 cause of this. In the first place, most of the easily de- 

 composed liquids are solutions in water, of acids, alkalis 

 or salts, and this has naturally attracted attention. In 

 the second place, these solutions are all ones in which 

 double decompositions, and such-like chemical actions 

 take place with facility. Can a common explanation be 

 given of this remarkable coincidence of electric conduc- 

 tivity and chemical activity ? Electric conductivity is due 

 to two causes^ — first, the^electric charges on the ions ; and 

 second, the independent mobility of these oppositely 

 charged ions under electric force. Without entering 

 upon the very interesting questions involved in in- 

 numerable speculations as to the causes of these 

 charges and of the mobility of the ions, all modern 

 theories acknowledge that, in some way or another, 

 water, and some other liquids in a less degree, 

 have the very remarkable property of conferring upon 

 certain substances dissolved in them the wonderful inde- 

 pendent mobility of the ions which we see in electrolysis. 



