August 17, ign] 



NATURE 



215 



for we must, I think, recognise hereabouts a younger 

 Boulder Clay as distinct from the *' Chalky Boulder Clay 

 of the Herts and Essex plateau, along with interglacial 

 leposits consisting largely of the outwashings of the older 

 Clay. 



It is easy to understand that a great latitudinal range of 

 variations of climatic conditions in these lowland regions 

 of south Britain would be necessarily contemporaneous 

 with the more definitely marked altitiuiiiial variations of 

 the snow-line in the Alpine regions of Britain and Europe, 

 whether from regional subsidence or otherwise. One may 

 venture to say that we have here a record contemporaneous 

 perhaps with that of the " Hessle Boulder Clay " or the 

 " Purple Boulder Clay " (.Brit. Mus. " Guide to the Stone 

 Age," p. 8), and with the " Wurrn " l.vierte Yergletscher- 

 ung) of Alpine glaciation (Credner, " Geologie," tenth 

 edition, p. 739) ; also Werth, Globus, Band xcvi.. No. 15, 

 p. 231). A. Irving. 



Bishop's Stortford, August 9. 



The Anti-kathodes of X-Ray Tubes. 



The special requirements to be fulfilled by materials 

 adapted for use as anti-kathodes are somewhat exacting, 

 and the range of such materials is therefore limited. It 

 is, further, unfortunate that the platinum, tantalum, &c, 

 are in general costly, and that the expense of X-ray tubes 

 is hence, considering their life, high. In casting about 

 for some means of avoiding this difficulty it has occurred 

 to me that carborundum, a material now quite familiar as 

 an abrasive, might be a suitable facing for the anti- 

 kathode. Carborundum, being a product of the electric 

 furnace, is exceedingly refractory ; electrically it is a very 

 bad conductor. Messrs. Helm have constructed for me a 

 tub" fitted with an anti-kathode from a square inch of 

 carborundum grinding slip, and I have used this tube, so 

 far as my limited laboratory means allow, with perfectly 

 successful results. My coil is only of low power, and I 

 have no means of making any comparative tests of a 

 quantitative type. It seems likely, on theoretical grounds, 

 that the emission from such a tube would be of low 

 penetrative power, but, so far as I can judge, the tube 

 does not seem to pass so readily into the hard condition. 



My object in this letter is to bring this matter to the 

 notice of others who are in a position to test the properties 

 of carborundum as an anti-kathode material. If its radia- 

 tion is of a low penetrative type, such a tube might have 

 advantages in certain superficial treatments in electro- 

 therapeutics, e.g. ringworm of the scalp, &c. T should be 

 greatly interested in hearing of any experimental trial. 



J. ScHOFIELD. 



Technical School, Keighley. 



The Action of Carbon Dioxide on Litmus. 



I write to direct attention to the inaccuracy of a 

 common statement in elementary text-books describing the 

 action on litmus of carbon dioxide in solution. 



It is generally stated that the action of carbon dioxide 

 is to turn litmus " wine red," while the fact is that carbon 

 dioxide dissolved in distilled water turfts neutral litmus red, 

 just like any other acid. 



The cause of the wine-red colour usually obtained is the 

 presence of alkaline bicarbonates as impurities. That this 

 is the case can be seen by adding a drop of ammonia or 

 of sodium carbonate solution to the carbon dioxide solu- 

 tion, when the colour changes, first, from red to blue, and 

 then, after an interval which depends on the amount of 

 alkali added, to the wine red usually associated with the 

 action. A weak solution of lime water acts similarly, and 

 this would seem to give the genesis of the error, as if 

 hard waters are used to make up the solutions the wine- 

 red colour is produced. 



The point may not be of the greatest consequence, but 

 it lines not seem to lie generally known, and the columns 

 of Nature would seem to offer the best means of dis- 

 cing, to those whom it chiefly concerns, the know- 

 ledge of another " text-book " error. 



M. M'Callum Fairgrieve. 



The Edinburgh Academy, July 26. 



NO. 2l8l, VOL. 87] 



THE BUSHOSGO: AN ETHNOGRAPHICAL 

 STUDY OF THE CENTRAL CONGOLAND 

 PEOPLES. 1 

 T T is difficult to write an adequate review of this 

 -l work, the result of Mr. Emil Torday's last ex- 

 pedition to central Congoland (1907-9), an expedition 

 in which he was accompanied by Mr. M. W. Hilton- 

 Simpson and a very clever painter, Mr. Norman H. 

 Hardy. Mr. Torday has had the advantage of the 

 collaboration of Mr. T. A. Joyce, of the British 

 Museum and the Royal Anthropological Institute, and 

 Mr. Joyce has been able to bring to bear on the com- 

 pilation his exceptional knowledge of negro arts, im- 

 plements, customs, religious beliefs, morals, laws, 

 social life, games, songs, and folklore. 



The water-colour drawings by Mr. Norman H. 

 Hardy are, beyond all question, the best that have 

 ever been executed so far in Negroland. They have 

 the absolute fidelity of photographs, with at the same 



f the Bangongo 



time an appreciation of composition and colour which 

 makes them really works of art. Special instances 

 to justify this praise are : — Plate 5, a masked dancer 

 of the Bangongo (Fig. 1) ; plate 7, female dancers 

 amongst the Bangongo; plate S, a Bangongo em- 

 broideress ; plate 9, a portrait of a Bangongo black- 

 smith ; plate 11, Shika, a young girl of the Isambo 

 tribe; plate 12, a young- Bashilele man, with the 

 profile of an ancient Egyptian (Fig. 2); and amongst 

 the black-and-white drawings, plate 17, a studv of a 

 native engaged in the manufacture of vegetable salt 

 (Fig. 3), together with certain interiors of houses. 

 Three of the plates referred to are here reproduced in 

 a reduced form. 



1 4 Notes Ethnographiques sur les peuples communement appelcs Bakuba, 

 ainsi que sur les peuplades apparentees. Les Bushongo." By R. Tordey 

 and T. A. Joyce. Annales du Musee du Congo Beige. Publiees rar la 

 Ministere des Colonies. Ethnographic. Anthropologic — Sene III : Docu- 

 ments Ethno^raphiques concernant les populations du Coneo Beige. 

 Tome II. — Fascicule I.— Coloured illustrations by Norman H. Hardy. 

 Published by the Museum of the Belgian Congo, Brussels. 



