J (JLY 1 6, 1908] 



NATURE 



247 



■ The Magnetic Separation of Heavy Minerals in the 

 Field. 



For some time I have been trying to tind a simple and 

 rapid field method of separating the magnetic and faintly 

 magnetic from the non-magnetic minerals in the residue 

 obtained by panning a river sand or gravel. In the labora- 

 tory this is usually done by means of the electromagnet. 

 1 have experimented in the field with a portable electro- 

 magnet, but, apart from the disadvantages of weight, 

 bulk, and clumsiness of manipulation, the dynamo is readily 

 liable to go out of order and render the whole apparatus 

 useless. My colleague, Mr. Longbottom, has experimented 

 with a compound magnet composed of three or four simple 

 horseshoe magnets bound together and fitted with adjust- 

 able poles. 'Ihis gives admirable results, and is to be re- 

 commended for fractional separations, but the constant 

 adjusting and re-adjusting of the poles becomes tedious in 

 actual practice. 



I find, however, that all the advantages of the electro- 

 magnet can be obtained in the field by the combined use 

 of an ordinary large (.S-incli) horseshoe magnet and a pen- 

 knife. .K small quantity of the residue to be examined is 

 taken, and the magnetite removed in the usual way. The 

 magnet is then held vertically over the sample, and the 

 bright steel blade of a penknife laid flat across one of the 

 poles with the back of the blade downwards. By gradually 

 appro.ximating the point of the blade to the other pole, and 

 thus narrowing the space between the poles themselves, 

 the power of the magnet is increased, and not only iron 

 ores, but all the dark-coloured silicates and garnets can 

 be rapidly and completely removed from the sample. The 

 residue may then contain such valuable minerals as tin- 

 stone and monazite, which when in small quantity are 

 frequently masked by the other minerals present. This 

 method has the further advantage that any single grain 

 can be rapidly tested by turning the point of the blade 

 slightly down below the level of the poles and bringing it 

 close to the grain in question. 



As an invaluable field method, as a useful laboratory 

 method where an electromagnet is not available, and as 

 an actual working method for teachers of practical geology, 

 I can recommend the one above described for simplicity, 

 ine.xpensiveness, and trustworthiness. 



J. D. Falconer. 



Zaria, Northern Nigeria, May 24. 



The Sky Glows. 



These phenomena on about June 30 and July i, referred 

 to in my letter iNatuke, July 9, p. 22 ij, I termed displays 

 of Aurora;, and was prompted to apply that title by the 

 descriptions given in some of the London newspapers, 

 which staled that well-defined streamers had been observed 

 from the metropolis. 



But certain features of the glows struck me as being 

 essentially different from exhibitions of normal Aurorae 

 Boreales. No streamers whatever were seen here, but my 

 view is somewhat restricted at low altitudes, and I thought 

 they might have evaded recognition. The clouds observed 

 were of peculiar character, and some of them showed traces 

 of spiral formation. Though thin, they were strongly 

 illuminative, and stars shone through them with surprising 

 distinctness. 



Here the display ranged over four nights, for on June 29 

 the sky was very light, and stars and Milky Way extremely 

 faint, but clouds were very prevalent. On July 2 some 

 attractive, coloured-cloud scenery was presented in the north- 

 west and north, but the sky had not the bright, weird aspect 

 it wore on preceding nights, and after midnight I saw 

 nothing unusual. 



Sounds proceeding from the north were strikingly audible 

 in the still air, and I never remember to have heard the 

 noise from distant railway trains in north-east so loudly 

 before. 



Whatever the true nature of the recent exhibition may 

 have been, it is certain that something in the air exercised 

 the capacity of reflection in a very high degree. The period 

 was one of great heat and thunderstorms. 



During past years, while engaged in meteoric or tele- 

 scopic observation, I have occasionally noticed great differ- 



XO. 2020, VOL. 78] 



ences in the transparency of the air. Occasionally the 

 lightness of the firmament has struck me as being due 

 to influences beyond local atmospheric causes. The 

 variations have been great without palpable reasons, but 

 no doubt there are different explanations applicable, though 

 the observer finds it difficult to assign satisfactory ones in 

 all cases. W. F. Denning. 



A Remarkable Solar Halo. 



On July 2, one of the days on which Miss Stevens saw 

 a halo at Oxford (Nature, July 9, p. 221), a very bright 

 halo was visible in the neighbourhood of Torbay.' I first 

 noticed it about 9 a.m., and it remained visible' well into 

 the afternoon. It attained its greatest brightness from 

 n a.m. until noon. On looking at it through dark 

 glasses it exhibited a somewhat remarkable form ; the 

 main halo had the usual radius of about 22°, but east 

 and west were arcs of which the greatest distance from 

 the sun was about 25° ; these arcs gradually ran into 

 the 22° halo. The effect was somewhat as though an 

 elliptical halo were superposed on a circular one, the 

 parts where the two coincided being of enhanced bright- 

 ness. Below the sun there were at times fragments of 

 halo at 44°. Masses of cirrus drifting from an easterly 

 direction passed across the halo at times and partially 

 obscured it, but probably h.ad no part in its formation ; 

 it could be seen shining through the thinner parts of 

 these clouds, and it regained its brightness as soon as 

 they passed over. The halo was evidently formed by thin 

 clouds above the ordinary cirrus, but no definite structure 

 was visible to enable one to determine which way this 

 layer was moving. Charles J. P. Cave. 



Bvunhilda, R.V.S., Fowey, July 12. 



Proposed Admission of Women to the Fellowship of 

 the Chemical Society. 



As president of the Chemical Society, I shall be glad if 

 you will publish the accompanying letter referring to the 

 correspondence as to the admission of women to the Fel'ow 

 ship of the Chemical Society which appeared in Nature 

 of July 9. W. Ramsay. 



Vou have doubtless received a letter emanating from 

 Oxford dated July i enclosing a circular and copy of 

 the petition recently presented to the Council of the 

 Chemical Society requesting the Council " to take such steps 

 as may appear desirable to ascertain the wishes of the 

 Society as a whole in regard to this question." 



The envelope enclosing the above communications bore 

 the familiar printed address-slips which might well lead 

 Felloyvs to conclude that they were issued by authority 

 of the Council. This is not the case. 



The Council resolved that the statement of arguments 

 on both sides yvhich yvas issued to Fellows on June 23 

 was better calculated to elicit an unbiassed opinion of all 

 Fellows if sent alone. 



The course adopted by the signatories of the Oxford 

 circular of July i is, therefore, not only unauthorised, but 

 is in direct opposition to a resolution of the Council of 

 which the signatories are members. 



W. Ramsay (President). 



Horace T. Brown (Foreign Secretary). 



Alex. Scott (Treasurer). 



M. O. FORSTER 1 /c- I ■ \ 



. IT .^ ]-(ScLretartes). 



.Arthur W . Crossley/^ ' 



LinnsEUs's Authorities. 



I should be very much obliged if any of your readers 

 could supply me with the full titles of the works cited by 

 Linnajus as follows in the twelfth edition (1766) of the 

 " Systema Naturae," p. 33 : — 



" Bont. jav. 84 t. 84; Koep. itin. c. 86; Dalin. Orat. 5." 

 I have looked up the works of Bontius in the British 

 Museum, but they are not ad hoc. Also where, if any- 

 where, did D. Braad publish an account of his journeys to 

 India? Karl Pearson. 



Blometric Laboratory, L'niversitv College, London. 



