3:^9 



NATURE 



[November 17. 1921' 



or practically zero when a monochromatic blue or 

 green filter is used. The only precaution necessary 

 is to cut out the extra resistance when starting up, 

 as the arc tends to strike on to the ioniser spiral. 



By using a sliding resistance of 800 ohms (suitably 

 protected) fastened to the bench near the microscope, 

 where it can be found and adjusted without moving 

 the head from the eyepiece, complete control over the 

 lighting is obtained, and the optimum intensity for 

 any combination of any eyepiece, objective, condenser, 

 and light-filter becomes possible with fully critical 

 illumination. 



Apart from the reduction of optical fatigue, the 

 system has the further advantage of rendering fine 

 detail more easily visible, and in cytological work the 

 achromatic structures are much plainer. When work- 

 ing with the Abbe drawing apparatus the difficulty of 

 balancing the illumination of the field and the draw- 

 ing surface is eliminated. 



There is nothing new in the use of a resistance 

 with an electric lamp for microscope work, but users 

 of " Pointolites," with all their advantages over other 

 types, may be interested to know that such control 

 is feasible. H. J. Denham. 



Botanical Laboratory, British Cotton Industry 

 Research Association, Shirley Institute, 

 Didsburv, Manchester, November 11. 



The Aurora Borealis of September 28-29. 



With reference to my letter in Nature of October 6 

 on the observation of the aurora on the night of 

 September 28-29 ^"<^ Father Cortie's record of the 

 accompanying magnetic storm (Nature, October 27), 

 I have just received a communication from Mr. J. W. 

 Young, of Glasgow, a portion of which may be of 

 interest in the above connection : — 



" It may interest you to know that by my records 

 I find I also saw this. The back of my house (on 

 south-west of Glasgow) gives me a clear view of 

 jsome twenty miles along the Loch Lomond valley 

 in the direction of magnetic north, and for some years 

 .it has been my practice to keep watch for such occur- 

 rences, much more frequent here than most are aware. 

 Usually 8-1 1 p.m. is the period of greatest brilliancy, 

 and the streams of yellow, pink, and green light 

 sometimes extend, pulsating, almost to the zenith. . . ." 



William J. S. Lockyer. 



Norman Lockyer Observatory, Salcombe Hill, 

 Sidmouth, S. Devon, November 7. 



Applied Anthropology. 



I was, unfortunately, unable to take part in the 

 discussion on a possible Anthropological Service at 

 Edinburgh, referred to in the leading article in 

 Natl-re of November 10, but there is one point on 

 which I would have insisted had I been present : the 

 danger of a little knowledge. Anthropology is funda- 

 mentally a branch of biology, not of literature or 

 philosophy, except in so far as the latter is biological. 

 It is, perhaps, the most complicated of all the branches 

 of biology, and the branch in which the collection of 

 precise data is the most difficult. To me it is incon- 

 ceivable that a sound knowledge of anthropology can 

 be obtained without a preliminary training in bio- 

 logical method. At present anthropological studv, 

 especially that of the physical or anatomical side, is 

 in a state of chaos, largely because the comparative 

 studertt has to make use of information of all degrees 

 of accuracy or the reverse — mostlv the reverse. What 

 a missionary said two hundred years ago may carry 

 NO. 2716, VOL. 108] 



greater weight than a recent investigation on sound 

 scientific lines. , - - .s 



My own investigation's in the Malay Peninsula and 

 my more recent experience as a Government official in 

 India have taught me the disadvantages under which 

 an official labours in collecting anthropological in- 

 formation, and I think that most scientific men in 

 the employment of any Government would agree with 

 me in their hearts that there is no danger more to be 

 feared in scientific administration than the interference 

 of the administrative officer who possesses, or is led 

 to think he possesses, a peculiar, but superficial, know- 

 ledge of any branch of science. 



If anthropology is a branch of science, or rather, 

 as I believe, a complex of the terminal twigs of several 

 distinct branches, it must be studied seriously and 

 scientifically, not merely tacked on as a kind of floral 

 decoration to a classical or commercial education. 



N. Annandale. 



Abden House, Marchhall Crescent, Edinburgh, 

 November 11. 



Use of Carborundum for Ruling Test Plates. 



The communication frorn Mr. A. Mallock in 

 Nature of September i, p. 10, reminds me of the 

 marked success that I have had in the use of fine 

 carborundum points for scratching on glass. Some 

 years ago, when confronted with the task of pre- 

 paring small oscillograph mirrors from microscope 

 cover-glasses, I found that a small fragment of car- 

 borundum crystal tied in the split end of a match or 

 forced into a piece of soft rubber for a handle made 

 an excellent glass-cutter. The scratches were so fine 

 and clean-cut that the glass could easily be broken 

 into very narrow strips. 



Although very hard and sharp, the points are wide- 

 angled, the angles as viewed in a microscope appear- 

 ing to be in the neighbourhood of 90°. 



It seems possible that these crystals, if the pressure 

 were sufficiently light, might be used to rule lines on 

 thin films of aniline colours without scratching the 

 glass. W. G. Cady. 



Wesleyan University, Middletown, Conn., 

 October 22. 



Bee-sting and Eyesight. 



I WAS stung in my left eye by a. bee yesterday just 

 above the eyelid. Within an hour and a half that 

 eye became almost insensitive to light, but quickly 

 recovered. In the first stage of recovery it was prac- 

 tically colour-blind, and when the other eye was 

 closed objects appeared as seen by the light of a 

 sodium flame or a mercury arc light. To-day the eye 

 has fully recovered. I am wondering whether other 

 of vour readers can record a similar experience. 



J. W. GiFFORD. 



Oak'ands, Chard, October 21. 



The Age of the Earth. 



With regard to Lord Rayleigh's letter (Nature. 

 November 10), I think my use of the word "sugges- 

 tion," instead of "statement," for example, suffi- 

 ciently indicated that I appreciated the fact that he 

 did not definitely assert that the earth was becoming 

 hotter. I am glad to find that his views and mine 

 are not in essential disagreement. 



Harold Jeffreys. 



Meteorological Office, South Kensington, 

 London, S.W.7, November 15. 



