September 12, 1912 



NA'l URE 



Zl 



African naturalists to settle this question. In Natal 

 Mr. G. F. Leigh, the late Mr. A. D. Millar, and Miss 

 Fountaine have been successful in breeding the two 

 Pseudacraeas, lucretia and imitator, but the latter, 

 which is the only Natal member of Dr. Jordan's 

 group, appears in a single form mimetic of Planema 

 aganice, and is therefore incapable of supplying the 

 desired test. I attempted to induce both Miss Foun- 

 taine and Mr. Millar to travel to Entebbe in order 

 to decide the question. My friend Mr. VV. A. Lam- 

 born, who has done such splendid work in breeding 

 Lepidoptera in the Lagos district, has reared P. lucretia 

 and also P. semire — the latter, I believe, for the first 

 time — but has not yet been successful in finding the 

 larva; or in obtaining the eggs of any local form of 

 P. curytus. 



Lately, however, I have felt confident that success 

 would be achieved by Dr. Carpenter, with his wide 

 experience of breeding and residence in an exception- 

 ally favourable locality. He first succeeded in finding 

 and rearing the larva of P. lucretia, and then made 

 many attempts to obtain eggs from captured females 

 of the liobleyi group. Discouraged by many failures, 

 he was beginning to despair when, some weeks past, 

 he observed in the Bugalla forest a female obscura 

 "with a touch of hobleyi" settling in an unusual 

 position on a leaf of the food-plant of lucretia — almost 

 certainly a Sapotaceous plant. The butterfly escaped, 

 but Dr. Carpenter found the egg on the leaf, and 

 hoped to rear the perfect insect before or during the 

 meeting of the Second International Congress at 

 O.^ford (August 5-10), and he promised that if the 

 offspring turned out to be terra or hohleyi, he would 

 cable the result. He wrote that he anticipated terra, 

 because this form is much the commonest on Bugalla. 



Unfortunately the eagerly-expected butterfly did not 

 emerge until after the meeting, but on August 19 I 

 received a cable from Entebbe with the word "terra." 

 Furthermore, Dr. Carpenter has now succeeded in 

 obtaining eggs laid by known parents upon enclosed 

 branches of the food-plant in the forest, so that we 

 shall not have to wait long for evidence that is toler- 

 ably certain to afford direct proof of Dr. Jordan's 

 conclusions as regards all the forms of the hobleyi 

 group on the island, and is likely to establish the 

 genetic relationship between them. 



Dr. Jordan, Mr. Wiggins, Mr. Neave, and Dr. 

 Carpenter are all to be warmly congratulated on the 

 parts they have played in solving a bionomic problem 

 of extraordinary interest and complexitv. 



E. B. POULTON. 



St. Helens, Isle of Wight, August 28. 



Wireless Telegraphy and Terrestrial Magnetism. 



The report in Tltc Times of the discussion on wire- 

 less telegraphy at the British Association meeting in 

 Dundee mentions the hypothesis — introduced appar- 

 ently by Dr. Eccles — that several of the phenomena of 

 the propagation of electric waves round the earth are 

 largely influenced by the existence of an ionised layer 

 in the atmosphere. The hypothesis seems analogous 

 to, if not identical with, one made by several mag- 

 neticians independently, with the object of explaining 

 phenomena exhibited by the diurnal variation of the 

 magnetic elements. This diurnal variation is now 

 generally regarded as most probably due to electric 

 currents in the upper atmosphere, and it has been 

 suggested that the fact that the magnetic changes are 

 normally larger by day than by night is due to an 

 increased ionisation of the atmosphere due to sun- 

 shine. 



The regular diurnal magnetic variations are much 

 larger in years of many than of few sun-spots. The 

 NO. 2237, VOL. 90] 



difference between the size of the day and night move- 

 ments is relatively reduced in years of sun-spot maxi- 

 mum, and in all years during large magnetic storms. 

 Again, the diurnal variation is much larger in high 

 latitudes — where aurora abounds— than elsewhere, 

 and the difference between day and night 

 phenomena is there much reduced. Finally, it 

 has been recently found that a substantial 

 part of the magnetic sun-spot relationship may be 

 explained by a direct connection between the ampli- 

 tude of the diurnal magnetic range and the spotted 

 area of the sun some four days previously. These 

 phenomena, or at least some of them, have been 

 ascribed to corresponding changes in the ionisation of 

 the upper atmosphere. 



The natural inference, in short, is that the ionisation 

 is much enhanced in years of sun-spot maximum and 

 during magnetic storms, and is substantially influ- 

 enced by the sun-spot area four days previously. Also 

 one would infer that in high latitudes the upper atmo- 

 sphere is normally much more highly ionised than 

 elsewhere. If wireless telegraphy is largely dependent 

 on an ionised layer, then unless this layer is distinct 

 from that which influences terrestrial magnetism, we 

 should expect wireless phenomena to show peculiarities 

 corresponding to those just described in terrestrial 

 magnetism. My object in writing this note is to 

 direct the attention of those in control of wireless 

 installations to the field of research which is thus sug- 

 gested. Wireless telegraphy may yet lend itself to the 

 direct experimental investigation of the causes of a 

 variety of the phenomena of terrestrial magnetism. 



September 7. C. Chree. 



On the Structure of the Stromatoporoid Skeleton, 

 and on Eozoon. 



I H.AVE pointed out (.Annals. Mag. Nat. Hist., 

 September, 1912) that Stromatoporoids are Foramini- 

 fera, but I did not give an explanation of the struc- 

 ture of the skeleton. I now find that the clue to this 

 structure lies in the " astrorhizse " or stellate patterns 

 on the surface of many of these fossils. 



Each astrorhiza consists of a spiral series of 

 charnbers formed round a central and a circum- 

 ambient chamber, and the existence of a number of 

 astrorhizce is due to budding — as in corals. Anyone 

 who has been bewildered — as I have been — at the 

 apparent complexit}' of Stromatoporoid structure will 

 at once appreciate — I cannot forbear saying — the 

 beautiful simplicity of this solution of a difficult 

 problem, and will realise that these organisms have 

 at last come to rest in their proper place. I am 

 publishing in the October number of the .Annals a 

 revised classification of the group. 



Eozoon canadense likewise is a colony-forming 

 Foraminiferan, the unit in this case being a coiled 

 Nummulitid shell. Convincing evidence for this state- 

 ment also will be given in the October number of the 

 -Annals Mag. Nat. Hist. 



In view of a possible recrudescence of the Eozoon 

 controversy, it is very fortunate that the evidence in 

 favour of the theory of organic origin is now so over- 

 whelminsr that the former opponents of that theory 

 will readily change their views. R. Kirkpatrick. 



British Museum (Nat. Hist.). 



The Striation of Stones in Boulder Clay. 



Is' Natuke of September 5, Dr. A. Irving, in 

 ciiticism of statements by Air. Reid Moir, asks 

 " how could the soft matrix of the Boulder Clay 

 scratch a flint, or even hold a harder stone with 

 sufficient grip to give it effect as a graving-tool ? " 



