sc/EycEGOss/r. 



373 



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fiiNHUi ll;|) IIV JAMKS (JUllK. 



A V'Ai.i'i'M Ki,i;< iKOSi'oi'K. -I•Aperimclll^ have 

 riccnlly liccn iiKiilc Ijy Pfliumi in prove- that at llic 

 hijjiit'si vncuum ol)iainalilo flcclrical fcirccs arc still 

 exerted. A pear-shaped electroscope was constructed, 

 havinj; two strips of aUuniniuni foil suspended inside 

 and attached to an aluminium plate. The vessel was 

 then exhausted to as hiyh a vacuum as possible, and 

 the movements of the leaves recorded when a charge 

 was yiven to ihem. It wa-. found that electrostatic 

 effects look place with j^reat energy, no lag taking 

 place owing to absence <if air resistance, .\ctual dis- 

 charges app;irently cease through the high vacutnii, 

 not the slightest luminous eflects being observed. 

 The construction of such an electroscope is, however, 

 a dirticult matter. 



KiiNTGKN Rays ami Selenium. - .\ marked 

 effect is observed if a selenium cell is exposed to the 

 action of an X-ray tube at a short distance. In one 

 particul.tr observation, recently m.adc, when the X-ray 

 lube was at a distance of 5 cm from (he cell, the 

 resistance of the latter fell quickly from 40,chx) ohms 

 to 34,000 ohms, and kept oscillating aliout the latter 

 value, owing probably to variations in the intensity 

 of the rays. When these ceased to act, the cell re- 

 gained its . normal conductivity more slowly than it 

 does after the imp.icl of light. The above diminution 

 in the resistance of ihe cell was the same as woulil be 

 produced by a gas-jet placed at a distance of f5 

 metres. The action of the rays diminished with 

 increasing distance, but was still sensible at 17 cm. 



Soi.in Hydrogen. — This formed the subject of a 

 lecture of absorbing interest delivered by Professor 

 Oewar before a crowded and appreciative audience 

 at the Royal Institution on April 6th. No one can 

 speak with so much authority upon this line of 

 investigation as Professor Dewar, as it is to him the 

 honour is due of having reached a nuich lower tempera- 

 ture than any other investigator. Prefacing his dis- 

 course by a few general words, he very clearly led 

 his audience through many details of his brilliant 

 researches of the past few \'ears : illustrating his 

 remarks with several successful experiments. Liquid 

 air and licpiid hydrogen were freely used as if they 

 only cost a few shillings a pint to prepare, instead of 

 being the very expensive luxuries that they arc really. 

 Professor Dewar showed that whereas it is possible to 

 solidify nitrogen solely by the cold due to evaporation 

 cnnsetjuent \ipon reduced pressure, it is impossible to 

 Milidify oxygen in this way. The latter gas was 

 >olidified, however, during the lecture by surrounding 

 it in a proper manner by liquid hydrogen ; the solid 

 mass, as a white opacpie powder being thrown out 

 on the lecture table in full view of the audience. 

 .Solid hydrogen wa.s afterwards successfidly obtained 

 in a sontewhat similar manner, this particular experi- 

 ment eliciting unanimous applause owing to the 

 temperature of the mass being practically the lowest 

 ever attained — namely, 15° upon the absolute scale, 

 or 258° C. below the freezing-point of water. Pro- 

 fessor Dewar has been able to reach a slightly lower 



leinpernuirc than (his, about 13° above the alimlutc 

 icxQ, but, as he |><)inted out, the difticullien en- 

 countered in iluis obtaining a temjieralure of even 

 1° l)elow the melting-|)oint of hydrogen are enormous. 

 .\nother experiment performed was one illustrating 

 the work of Professors Dew.ir and Fleming on the 

 electrical conductivity of metals at extremely loH< 

 temperatures. .\ circuit was arrarig. il including an 

 incandescent lamp and a coil of wir . The current 

 was so regulateil that it was just sunlcient to keep 

 the fdament of the lamp at a ilull red heat when the 

 coil of wire was at the ordinary tenip<,ratures. The 

 coil was then immersed in liquid hydrogen and, 

 therefore, brought to an exceedingly low tempera- 

 ture. This resulted in a reduction of the resistance 

 of the wire, more current consequently flowing 

 through the lamp, which glowed very brilliantly. 



.Vn ICi.Kt I khai. .\Ihro.\iktek. \\ the last 

 meeting of the Physical Society of London, Mr. P. K. 

 Shaw described a very delicate instrument, an 

 electrical micrometer, which he had devised to 

 measure extremely small distances. It con.sists 

 essentially of a screw with a pitch of 0*5 mm, and 

 having a head divided into 500 parts. This screw 

 presses against the long arm of an aluminium lever, 

 the short arm of which presses against the long arm 

 of another, and so on through three levers. The 

 motion of the spherometer screw can thus be trans- 

 mitted to a fuie plalino-iridium point close to a small 

 platino-iridium disc, which, in .Mr. Shaw's experi- 

 ments, was fastened to the centre of a telephone 

 diaphragm, the movements of which Mr. Shaw has 

 been investigating. By careful and accurate reading 

 an observable twist of the spherometer head corre- 

 sponds to a movement of one millionth of a millimetre 

 of the fine point. .Mr. Shaw h<-is found that he cannot 

 hear any .sounds from the telephone if the amplitude 

 of vibration of the diaphragm is less than 0'37 

 millionths of a mm. .\ motion of 5omillionthsgivcs 

 comfortable s(mnds, 1,000 millionths uncomfortable 

 sounds, and 5,000 millionths .sounds unbearably loud. 



Rai)Ii;m Rays. — Much important work upon these 

 mysterious emissions from radium has been done 

 lately by Becquerel and Curie. The latter ha.s 

 apparently proved without doubt thai the rays 

 emitted from radium are conijjosed of material 

 particles carrying negative electrical charges. From 

 first thoughts therefore it would appear that the body 

 emitting these rays would suft'er a loss in weight, but 

 M. Curie h.-Ls .shown that the charges carried off are 

 so feeble and the mass of matter so small that probably 

 some millions of years would be required to remove 

 one milligram in the case of the most intense radia- 

 tion that has yet been observed. 



Actinium. — Scarcely a week now p;i,sses without 

 some work being done in connection with new 

 elements, or with elements possessing emissive pro- 

 perties. Radium and polonium have been recently 

 discovered and investigated, particularly by M. and 

 Mme. Curie, and now a new radio-active element is 

 reported to have been discovered by M. Deljierne. 

 who names it .-Vctinium. It h.os been produced from 

 the residues from pitchblende and is precipitated h\ 

 the principal agents for titanium. With the rays 

 emitted by actinium it is possible to produce the 

 same phenomena as those of the rays emitted by 

 radium and polonium. Further, in an intense 

 magnetic field, the rays of actinium, or rather a por- 

 tion of the rays, are deviated and will impress a 

 photographic plate placed below a lead cell contain- 

 ing the .substance. 



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