i8 



NATURE 



\Jan. 6, 1 88 1 



covered thennometer rose ra|3idly till it nearly touched 94°, w hile 

 the naked one remained stationary. 



The conclusions to which these experiments point are too 

 obvious to require demonstration. C. J. McNally 



Madras, December 9, 1S80 



Selenium 



The use of selenium in the photoplione has suggested to me 

 the possibility of using it in tsvo vi'ays, which I shall now describe, 

 thinking you may perhaps consider theai of sufficient general 

 intere>t to publish in Nature. 



Firstly, it seems probable that selenium might be used to 

 obtain the automatic registration in a clironograph of such phe- 

 nomena as star transits. It possesses the property of being 

 drawn into fine wire at a low temperature, but whether it cm 

 be drawn fine enough to represent transit wires in a telescope I 

 do dot know. 



The aiTangement would be as shown in the diagram, \\here 

 A A B B are parallel metal plates cro.'ising the field of the tele- 



scope, and insulated from each other except by the selenium 

 wires C C c c in one direction, and by a wire circuit passing 

 through a battery, and a relay, R, in the other. The relay 

 should be so adjusted that the increased force of the current 

 pas-ing through the circuit caused by the light of a star falling 

 on each wire c c in succession, shall cause its armature to act, 

 and i>ass on a signal to the chronograph. 



The delicacy of the adjustment required for this purpose 

 might be a greater diiificulty than I am aware of; but it should 

 be borne in mind that the length of selenium in the circuit may 

 be very small, as the plates A A u B need no: be farther apart than 

 sufficient to insure the star's falling between them without exces- 

 sive accuracy of setting, say one-twentieth to one-tenth of an inch 

 in a telescope of moderate size. If necessxry, it would be simple 

 enough to give each wire c c its own distinct circuit. Should 

 the brittlene^s of the wires prove a difficulty, they may be sup- 

 ported between the plates A A B B in any convenient way which 

 does not interfere with the insulation of these plates. 



The second purpose would perhaps be of more practical use 

 than the above, viz. to secure an automatic daily time-signal. 



■jBaOery 



Let a thin plate of selenium be placed between, and in firm 

 contact with, two parallel plates of metal, which are connected 

 with each other by a wire passing through a battery and a relay 

 as above, so that the selenium alone interrupts the circuit. Tlien 

 if this plate be placed with its length in the meridian, and a 

 lens adjusted above it, so as to throw the image of a star, or the 

 sun, as it crosses the meridian exactly on the selenium, a 

 signal will be obtained from the relay as before, which in this 

 case may be the stroke of a bell or any other convenient sound. 



An ordinary lens would require constant changes of adjust- 

 ment if used for the sun, moon, or any body of varying 

 declination ; but if the lens were the central slice cut out of a 

 sphere by two small circles parallel to each other and equidistant 

 from the centre, placed with its flat sides jiarallel to the meridian, 



while the selenium was placed in a curve concentric with that of 

 the lens, at the proper distance fr.im its surface, and of sufficient 

 length — of course being accurately in the meridian — then any 

 heavenly body of whatever declination — between certain wide 

 limits — would throw its image on the selenium and afford a 

 signal, if of sufficient brightness. The arrangement of a warning- 

 signal would be easy. 



If this method proved practicable the objection would remain 

 of having to apply a correction to obtain mean time, which 

 would probably prevent its being used for public purposes, such 

 as dropping time-balls or firing time-guns. It seems to me how- 

 ever that it might nevertheless prove very useful to many private 

 individuals who require an accurate knowledge of time. 



Poona, December 3, 18S0 W. M. C. 



Experiments with Vacuum Tubes 

 At a meeting of the Thilosophical .Society of Glasgow on 

 December 22, iSSo, I gave a ve. brief preliminary account of 

 some experiments that I have b.en making, along with Sir 

 William Thomson, with vacuum tubes. We have sealed up 

 English and German glass ttibes with very high vacuums, but 

 without any electrodes ; and have obtained very remarkable 

 luminous eftects both with the Ruhmkorf coil and also working 

 by means of electrostatic induction. Using an ordinary frictional 

 electric machine, and applying one end of a lon^ vacuum tube 

 to the prime conductor, while the other end of the tube is held 

 in the hand, the tube becomes charged as a double Leyden jar in 

 the following way : — one end of the tube, next to the prime con- 

 ductor, — outside positive, inside negative ; the other end — inside 

 positive, outside negative. This can be shown by the g>ild leaf 

 electroscope. The charges seem to be very high and the glass 

 is very frequently perforated. Indeed it is difficult to work with 

 the electric machine in tolerably good order without perforating 

 the glass. While this double Leyden jar is slowly discharged, 

 by removing, part by part, the charges from the outside of the 

 tube, beautiful luminous effect- are observed very different from 

 those seen in the ordinary vacuum tubes. We have also obtained 

 curious effects by heating the middle region of the tube so hi ;hly 

 that it becomes a semi-conductor. J. T. Bottomley 



Physical Laboratory, University, Glasgow, December 29 



Modern Use of Ancient Stone Implements 



Perhats the folbwiiig sla'ement will interest some of your 

 readers: — In an old volume, " Thomae Bartolini Acta hafni- 

 ensia," Ann. 1674, 1675, 1676, I find a paragraph signed by 

 Olaus Borriehius, which clearly indicites that in the seventeenth 

 century ancient stone implements, and probably many of them, 

 were converted into flints for the use of the contemporaneous 



musquetry. The text runs thus: — " Silices Anholdini trian- 

 gulares. Insula haec [Anholt in the Kattegat] porrigitur in sinu 

 codano, minuta ilia quiiem et naufragiis multorum infamis, uno 

 hic laudanda quod si quis arenas littoris eiusdem scrutetur, 

 infinitos reperiat silices nigros, albos, varios, in sabulo hinc inde 

 sepultos, ad sex transversos digitos in longitudinem protensos, 

 latos digiium unum, omnes triquetros ac si manu artificis 

 fuissent acuminati, et later. bus plerumque in illain aciem excitatis, 

 ut losuae servire potuerint cultris .saxeis filioruar Israel circum- 

 cisionem iniperanti. Nunc ferreo hic secul^ in alios vocantur 

 usus : malleo enim in frusta convenientia divisi sclopetorum 

 rotulis ignem prompte ministrant et fomitis incendiarii loco 

 fulmineis bellatorum tubis anciUintur." D. Budde 



Rome, December 26, 18S0 



Pile Dwellings 



If the connection bctiveen pile duellings in the Swiss lakes, 

 the Swiss chalet, and the Malayan modern pile dwellings is 

 demonstrated, a decided advance has been or will be made in 

 prehistoric anthropology. 



Pile dwellings are a very distinct characteristic of all the Hill 

 races north-east of Bengal, e.>tcept those on the Kasia Hill ranges, 

 and so far as I can see is a conspicuous distinction between the 

 Aryan and non-Aryan races here. 



The persistence with which this custom is retained among 

 tribes who have migrated to new sites, w here the need is not 

 obvious, seems to offer a safe means of tracing to some extent 

 racial descent or relationships. 



The " Miris " of Asam offer a case where part of the tribe is 

 still in its hills, while the rest are more or less scattered along 

 the Brahmaputra in the level land of Asam, and build houses 

 alike. The Ahoms, a Shan race who invaded and settled in 

 Asam in a.d. 122S, built pile dwellings, and the "Deodhaings," 

 who are lineally descended from them, do so now. The Butias 



