,,erne/ ,,ru!r=d ,,nobel ,,lecture ,decemb] #aa1 #aijh4 ,,! ,,*emical ,,nature ,,( ,,! ,,alpha ,,p>ticles ,,f ,,radioactive ,,sub/ances ,! /udy ( ! prop]ties ( ! -rays has play$ a notable "p 9 ! developm5t ( radioactivity & has be5 in/rum5tal 9 br++ to light a numb] ( facts & relation%ips ( ! fir/ importance4 ,) increase ( exp]im5tal k !re has be5 a gr[+ recognition t a l>ge "p ( radioactive ph5om5a is intimately connect$ ) ! expulsion ( ! -p>ticles4 ,9 ?is lecture an attempt w be made to give a brief hi/orical acc\nt ( ! developm5t ( our k ( ! -rays & to trace ! long & ardu\s pa? trodd5 by ! exp]im5t] 9 ! attempts to solve ! difficult "q ( ! *emical nature ( ! -p>ticles4 -rays 7 fir/ obs]v$ 9 #ahii z a special type ( radiation & dur+ ! la/ six ye>s !re has be5 a p]si/5t attack on ?is great problem1 :i* has f9ally yield$ to ! assault :5 ! res\rces ( ! attack seem$ almo/ exhau/$4 ,%ortly aft] 8 discov]y ( ! radiat+ p[] ( uranium by ! photographic me?od1 ,becqu]el %[$ t ! radiation f uranium l ! ,rntg5-rays possess$ ! prop]ty ( dis*>g+ an electrifi$ body4 ,9 a detail$ inve/igation ( ?is prop]ty1 ,i exam9$ ! effect on ! rate ( dis*>ge by plac+ successive lay]s ( ?9 alum9ium foil ov] ! surface ( a lay] ( uranium oxide & 0 l$ to ! conclusion t two types ( radiation ( v diff]5t p5etrat+ p[] 7 pres5t4 ,! conclusions at t p]iod 7 summ$ up z foll[s3 ,^! exp]im5ts %[ t ! uranium1 radiation is complex & t !re are pres5t at lea/ two di/9ct types ( radiation--"o t is v readily absorb$1 :i* w be t]m$ = conv5i5ce ! -radiation1 & ! o!r ( a m p5etrative "*1 :i* w be t]m$ ! -radiation4#a ,:5 o!r radioactive sub/ances 7 discov]$1 x 0 se5 t ! types ( radiation pres5t 7 analog\s to ! - & -rays ( uranium & :5 a /ill m p5etrat+ type ( radiation f radium 0 discov]$ by ,vill>d1 ! t]m -rays 0 appli$ to !m4 ,! names ?us giv5 soon came into g5]al use z a conv5i5t nom5clature = ! ?ree di/9ct types ( radiation emitt$ f uranium1 radium1 ?orium1 & act9ium4 ,on acc\nt ( _! insignificant p5etrat+ p[]1 ! -rays 7 at fir/ consid]$ ( little importance & att5tion 0 ma9ly direct$ to ! m p5etrat+ -rays4 ,) ! adv5t ( active prep>ations ( radium1 ,giesel 9 #ahii %[$ t ! -rays f ?is sub/ance 7 easily deflect$ by a magnetic field 9 ! same direction z a /ream ( ca?ode rays & consequ5tly appe>$ to be a /ream ( project$ p>ticles c>ry+ a negative *>ge4 ,! pro( ( ! id5tity ( ! -p>ticles ) ! electrons con/itut+ ! ca?ode rays 0 complet$ 9 #aijj by ,becqu]el1 :o %[$ t ! -p>ticles f radium _h ab\t ! same small mass z ! electrons & 7 project$ at a spe$ comp>able ) ! velocity ( light4 ,"t does n all[ me to ent] into ! lat] "w ( ,kaufmann & o!rs on ?is subject1 :i* has greatly ext5d$ our k ( ! con/itution & mass ( electrons4 ,9 ! meantime1 fur!r inve/igation _h disclos$ t ! -p>ticles produc$ mo/ ( ! ionization obs]v$ 9 ! neighb\rhood ( an unscre5$ radioactive sub/ance1 & t mo/ ( ! en]gy radiat$ 0 9 ! =m ( -rays4 ,x 0 calculat$ by ,ru!r=d & ,mc,clung 9 #aija t "o gram ( radium radiat$ a l>ge am\nt ( en]gy 9 ! =m ( -rays4 ,! increas+ recognition ( ! importance ( ! -rays 9 radioactive ph5om5a l$ to attempts to det]m9e ! nature ( ?is easily absorb$ type ( radiation4 ,/rutt 7,"l ,rayleigh7 9 #aija & ,sir ,william ,crookes 9 #aijb sugge/$ t !y might possibly prove to be project$ p>ticles c>ry+ a positive *>ge4 ,i indep5d5tly arriv$ at ! same conclusion f consid]ation ( a v>iety ( evid5ce4 ,if ?is 7 ! case1 ! -rays %\ld be deflect$ by a magnetic field4 ,prelim9>y "w %[$ t ! deflection 0 v slight if x occurr$ at all4 ,exp]im5ts 7 cont9u$ at int]vals ov] a p]iod ( two ye>s & x 0 n until #aijb1 :5 a prep>ation ( radium ( activity #ai1jjj 0 available1 t ,i 0 able to %[ conclusively t ! p>ticles 7 deflect$ by a magnetic field1 ?\gh 9 a v m9ute degree comp>$ ) ! -rays4 ,?is %[$ t ! -rays consi/$ ( project$ *>g$ p>ticles :ile ! direction ( deflection indicat$ t ea* p>ticle c>ri$ a positive *>ge4 ,! -p>ticles 7 %[n to be deflect$ also by an electric field & f ! magnitude ( ! deflection1 x 0 d$uc$ t ! velocity ( ! swifte/ p>ticles 0 ab\t #b4e x #aji cm p] second1 or "o-twelf? ! velocity ( light1 :ile ! value ( e_/m--! ratio ( ! *>ge c>ri$ by ! p>ticle to its mass--0 f\nd to be #e1jjj electromagnetic units4 ,n[ x is kn[n f ! data ( ! electrolysis ( wat] t ! value ( e_/m = ! hydrog5 atom is #i1fej4 ,if ! -p>ticle c>ri$ ! same positive *>ge z ! unit fundam5tal *>ge ( ! hydrog5 atom1 x 0 se5 t ! mass ( ! -p>ticle 0 ab\t twice t ( ! hydrog5 atom4 ,on acc\nt ( ! complexity ( ! rays x 0 recogniz$ t ! results 7 only approximate1 b ! exp]im5ts indicat$ cle>ly t ! -p>ticle 0 atomic 9 mass & might prove ultimately to be ei!r a hydrog5 or a helium atom or ! atom ( "s unkn[n elem5t ( light atomic weight4 ,^! exp]im5ts 7 repeat$ by ,des ,c\dres 9 #aijc ) simil> results1 :ile ,becqu]el %[$ ! deflection ( ! -rays 9 a magnetic field by ! photographic me?od4 ,?is pro( t ! -p>ticles consi/$ ( actual *>g$ atoms ( matt] project$ ) an enorm\s velocity at once ?rew a flood ( light on radioactive processes1 9 p>ticul> ^u ano!r important s]ies ( inve/igations :i* 7 be+ contemporane\sly c>ri$ on 9 ! ,laboratory at ,montreal 9 conjunction ) ,mr4 ,f4 ,soddy4 ,_h "t p]mitt$1 x w\ld h be5 ( int]e/ to consid] 9 "s detail ! nature ( ^! rese>*es :i* plac$ on a firm f\ndation ! n[ g5]ally accept$ trans=mation !ory ( radioactivity4 ,f a close exam9ation ( ! sub/ances ?orium1 radium1 & uranium1 ,ru!r=d & ,soddy _h rea*$ ! conclusion t radioactive bodies 7 9 a /ate ( trans=mation1 z a result ( :i* a numb] ( new sub/ances 7 produc$ entirely di/9ct 9 *emical & physical "* f ! p>5t elem5t4 ,f ! indep5d5ce ( ! rate ( trans=mation ( *emical & physical ag5cies1 x 0 recogniz$ t ! trans=mation 0 atomic & n molecul> 9 "*4 ,ea* ( ^! new bodies 0 %[n to lose its radioactive prop]ties accord+ to a def9ite law4 ,ev5 be=e ! discov]y ( ! mat]ial nature ( ! -rays1 x _h be5 consid]$ probable t ! radiation f any p>ticul> sub/ance accompani$ ! break+ up ( its atoms4 ,! pro( t ! -p>ticle 0 an eject$ atom ( matt] at once /r5g!n$ ?is conclusion & at ! same "t gave a m concrete & def9ite repres5tation ( ! processes occurr+ 9 radioactive matt]4 ,! po9t ( view rea*$ by u at t "t is cle>ly se5 f ! foll[+ quotation1 :i* ) little alt]ation holds good today4 ,! results obta9$ s f> po9t to ! conclusion t ! beg9n+ ( ! succession ( *emical *anges tak+ place 9 radioactive bodies is due to ! emission ( ! -rays1 i4e4 ! projection ( a heavy *>g$ mass f ! atom4 ,! portion left beh9d is un/able1 und]go+ fur!r *emical *anges :i* are aga9 accompani$ by ! emission ( -rays1 & 9 "s cases also ( -rays4 ,! p[] possess$ by ! radioactive bodies ( app>5tly spontane\sly project+ l>ge masses ) enorm\s velocities supports ! view t ! atoms ( ^! sub/ances are made up1 9 "p at lea/1 ( rapidly rotat+ or oscillat+ sy/ems ( heavy *>g$ bodies1 l>ge comp>$ ) ! electron4 ,! sudd5 escape ( ^! masses f _! orbit may be due ei!r to ! action ( int]nal =ces or ext]nal =ces ( :i* we h at pres5t no k4#b ,consid] = a mom5t ! explanation ( ! *anges 9 radium4 ,a m9ute fraction ( ! radium atoms is suppos$ ea* second to become un/able1 break+ up ) explosive viol5ce4 ,a fragm5t ( ! atom--& -p>ticle--is eject$ at a high spe$1 & ! residue ( ! atom1 :i* has a light] weight ?an be=e1 becomes an atom ( a new sub/ance1 ! radium emanation4 ,! atoms ( ?is sub/ance are f> m un/able ?an ^? ( radium & explode aga9 ) ! expulsion ( an -p>ticle4 ,z a result ! atom ( radium ,a makes its appe>ance & ! process ( dis9tegration ?us />t$ cont9ues ?r\gh a long s]ies ( /ages4 ,i c only ref] 9 pass+ "h to ! l>ge am\nt ( "w done by v>i\s exp]im5t]s 9 analys+ ! long s]ies ( trans=mations ( radium & ?orium & act9ium2 ! l9k+ up ( radium ) uranium & ! discov]y by ,boltwood ( ! long look$-= & elusive p>5t ( radium1 viz4 ionium4 ,?is phase ( ! subject is ( unusual int]e/ & importance b has only an indirect be>+ on ! subject ( my lecture4 ,x has be5 %[n t ! great majority ( ! transition elem5ts produc$ by ! trans=mation ( uranium & ?orium break up ) ! expulsion ( -p>ticles4 ,a few1 h[ev]1 ?r[ (f only -p>ticles1 :ile "s are rayless1 i4e4 und]go trans=mation )\t ! expulsion ( high-spe$ - & -p>ticles4 ,x is necess>y to suppose t 9 ^! latt] cases ! atoms break up ) ! expulsion ( -p>ticles at a spe$ too l[ to be detect$1 or1 z is m probable1 und]go a process ( atomic re>rangem5t )\t ! expulsion ( mat]ial p>ticles ( atomic dim5sions4 ,ano!r /rik+ prop]ty ( radium 0 soon se5 to be connect$ ) ! expulsion ( -p>ticles4 ,9 #aijc ,p4 ,curie & ,laborde %[$ t radium 0 a self-heat+ sub/ance & 0 always above ! temp]ature ( ! surr\nd+ air4 ,x seem$ probable f ! beg9n+ t ! effect mu/ be ! result ( ! heat+ effect due to ! impact ( ! -p>ticles on ! radium4 ,consid] = a mom5t a pellet ( radium enclos$ 9 a tube4 ,! -p>ticles are %ot out 9 great numb]s equally f all p>ts ( ! radium & 9 consequ5ce ( _! slight p5etrat+ p[] are all /opp$ 9 ! radium itself or by ! walls ( ! tube4 ,! en]gy ( motion ( ! -p>ticles is conv]t$ into heat4 ,on ?is view ! radium is subject to a fi]ce & unceas+ bomb>dm5t by its own p>ticles & is heat$ by its own radiation4 ,?is 0 confirm$ by ! "w ( ,ru!r=d & ,b>nes 9 #aijc1 :o %[$ t ?ree qu>t]s ( ! heat+ effect ( radium 0 n directly due to ! radium b to its product1 ! emanation1 & t ea* ( ! diff]5t sub/ances produc$ 9 radium gave out heat 9 proportion to ! en]gy ( ! -p>ticles expell$ f x4 ,^! exp]im5ts br\ght cle>ly to light ! enorm\s en]gy1 comp>$ ) ! weight ( matt] involv$1 :i* 0 emitt$ dur+ ! trans=mation ( ! emanation4 ,x c readily be calculat$ t "o kilogram ( ! radium-emanation & its products w\ld initially emit en]gy at ! rate ( #ad1jjj horse-p[]1 & dur+ its life w\ld give (f en]gy correspond+ to ab\t #hj1jjj horse-p[] = "o day4 ,x 0 ?us cle> t ! heat+ effect ( radium 0 ma9ly a second>y ph5om5on result+ f ! bomb>dm5t by its own -p>ticles4 ,x 0 evid5t also t all ! radioactive sub/ances mu/ emit heat 9 proportion to ! numb] & en]gy ( ! -p>ticles expell$ p] second4 ,we mu/ n[ consid] ano!r discov]y ( ! fir/ importance4 ,9 discuss+ ! consequ5ces ( ! dis9tegration !ory1 ,ru!r=d & ,soddy drew att5tion to ! fact t any /able sub/ances produc$ dur+ ! trans=mation ( ! radio-elem5ts %\ld be pres5t 9 quantity 9 ! radioactive m9]als1 :]e ! processes ( trans=mation h be5 tak+ place = ages4 ,?is sugge/ion 0 fir/ put =w>d 9 #aijb4c ,9 ! light ( ^! results & ! view t has already be5 put =w>d ( ! nature ( radioactivity1 ! speculation naturally arises :e!r ! pres5ce ( helium 9 m9]als & its inv>iable association ) uranium & ?orium1 may n be connect$ ) _! radioactivity1 & aga9#d4 ,x is !re=e to be expect$ t if any ( ! unkn[n ultimate products ( ! *anges ( a radioactive elem5t are gase\s1 !y w\ld be f\nd occlud$1 possibly 9 consid]able quantities1 9 ! natural m9]als conta9+ t elem5t4 ,?is l5ds support to ! sugge/ion already put =w>ds1 t possibly helium is an ultimate product ( ! dis9tegration ( "o ( ! radioactive elem5ts1 s9ce x is only f\nd 9 radioactive m9]als4 ,x 0 at ! same "t recogniz$ t x 0 q possible t ! -p>ticle itself might prove to be a helium atom4 ,z only weak prep>ations 7 !n available1 x did n seem feasible at t "t to te/ :e!r helium 0 produc$ f radium4 ,ab\t a ye> lat]1 ?anks to ,dr4 ,giesel ( ,brauns*weig1 prep>ations ( pure radium bromide 7 made available to exp]im5t]s4 ,us+ #cj milligrams ( ,giesel's prep>ation1 ,sir ,william ,ramsay & ,soddy 9 #aijc 7 able to %[ conclusively t helium 0 pres5t 9 radium "s mon?s old & t ! emanation produc$ helium4 ,?is discov]y 0 ( ! greate/ int]e/ & importance1 = x br\ght to light t 9 addition to a s]ies ( transition elem5ts1 radium also gave rise 9 its trans=mation to a /able =m ( matt]4 ,a fundam5tal "q imm$iately arose z to ! position ( helium 9 ! s*eme ( trans=mations ( radium4 ,0 ! helium ! end or f9al product ( trans=mation ( radium or did x arise at "s o!r /age or /ages8 ,9 a lett] to ,nature#e ,i po9t$ out t probably helium 0 d]iv$ f ! -p>ticles fir$ out by ! -ray products ( radium & made an approximate e/imate ( ! rate ( production ( helium by radium4 ,x 0 calculat$ t ! am\nt ( helium produc$ p] gram ( radium %\ld lie betwe5 #bj & #bjj cubic millimetres p] ye> & probably ne>] ! latt] e/imate4 ,! data available = calculation at t "t 7 imp]fect1 b x is ( int]e/ to note t ! rate ( production ( helium rec5tly f\nd by ,sir ,james ,dew>1 9 #aijh1 viz4 #acd cubic millimetres p] ye>1 is n f> f ! value calculat$ z mo/ probable at t "t4 ,^! e/imates ( ! rate ( production ( helium 7 lat] modifi$ z new & m accurate data became available4 ,9 #aije1 ,i measur$ ! *>ge c>ri$ by ! -p>ticles f a ?9 film ( radium4 ,assum+ t ea* -p>ticle c>ri$ ! ionic *>ge measur$ by ,j4,j4 ,?omson1 ,i %[$ t #f4b x #ajaj -p>ticles 7 expell$ p] second p] gram ( radium itself & f\r times ?is numb] :5 radium 0 9 equilibrium ) its ?ree -ray products4 ,! rate ( production ( helium calculat$ on ^! data 0 #bdj cubic millimetres p] gram p] ye>4 ,9 ! meantime1 by ! admirable rese>*es ( ,bragg & ,kleeman 9 #aijd1 our k ( ! "* ( ! absorption ( ! -p>ticles by matt] _h be5 mu* ext5d$4 ,x _h long be5 kn[n t ! absorption ( -p>ticles by matt] 0 diff]5t 9 _m respects f t ( ! -rays4 ,bragg %[$ t ^! diff]5ces arose f ! fact t ! -p>ticle1 on acc\nt ( its great en]gy ( motion1 0 n deflect$ f its pa? l ! -p>ticle1 b travell$ 9 ne>ly a /raight l9e1 ioniz+ ! molecules 9 its pa?4 ,f a ?9 film ( matt] ( "o k9d1 ! -p>ticles 7 all project$ at ! same spe$ & lo/ _! p[] ( produc+ ionization sudd5ly1 aft] trav]s+ a c]ta9 def9ite di/ance ( air4 ,! velocity ( ! -p>ticles 9 ?is view 7 r$uc$ by _! passage ?r\gh matt] by equal am\nts4 ,^! conclusions ( ,bragg 7 confirm$ by exp]im5ts ,i made by ! photographic me?od4 ,z a s\rce ( rays1 a ?9 film ( radium ,c1 deposit$ f ! radium-emanation on a ?9 wire1 0 us$4 ,by exam9+ ! deflection ( ! rays 9 a magnetic field1 x 0 f\nd t ! rays 7 homog5e\s & 7 expell$ f ! surface ( ! wire at an id5tical spe$4 ,by pass+ ! rays ?r\gh a scre5 ( mica or alum9ium1 x 0 f\nd t ! velocity ( all ! -p>ticles 7 r$uc$ by ! same am\nt & ! issu+ beam 0 /ill homog5e\s4 ,a rem>kable result 0 not$4 ,all -p>ticles app>5tly lo/ _! *>act]i/ic prop]ties ( ionization1 phosphoresc5ce & photographic action1 at exactly ! same po9t :ile !y 7 /ill mov+ at a spe$ ( ab\t #i1jjj kilometres p] second4 ,at ?is critical spe$1 ! -p>ticle sudd5ly vani%es f our k5 & c no long] be foll[$ by ! me?ods ( obs]vation at our comm&4 ,! use ( a homog5e\s s\rce ( -rays l radium ,c at once sugge/$ itself z af=d+ a basis = a m accurate det]m9ation ( ! value ( e_/m = ! -p>ticle & = see+ :e!r ! value 0 consi/5t ) ! view t ! -p>ticle 0 a *>g$ atom ( helium4 ,9 ! c\rse ( a long s]ies ( exp]im5ts1 ,i prov$ t ! -p>ticles1 :e!r expell$ f radium1 ?orium or act9ium1 7 id5tical 9 mass & mu/ consi/ ( ! same k9d ( matt]4 ,! velocity ( expulsion ( ! -p>ticles f diff]5t k9ds ( active matt] v>i$ ov] comp>atively n>r[ limits b ! value ( e_/m 0 con/ant & equal to #e1jgj4 ,?is value 0 n v diff]5t f ! "o orig9ally f\nd4 ,a difficulty at once arose 9 int]pret+ ?is result4 ,we h se5 t ! value ( e_/m = ! hydrog5 atom is #i1fej4 ,if ! -p>ticle c>ri$ ! same positive *>ge z ! hydrog5 atom1 ! value ( e_/m = ! -p>ticle w\ld indicate t its mass 0 twice t ( ! hydrog5 atom1 i4e4 equal to ! mass ( a hydrog5 molecule4 ,x seem$ v improbable t hydrog5 %\ld be eject$ 9 a molecul> & n an atomic /ate z a result ( ! atomic explosion4 ,if1 h[ev]1 ! -p>ticle c>ri$ a *>ge equal to twice t ( ! hydrog5 atom1 ! mass ( ! -p>ticle w\ld "w out at ne>ly f\r1 i4e4 a mass ne>ly equal to t ( ! atom ( helium4 ,i sugge/$ t1 9 all probability1 ! -p>ticle 0 a helium atom :i* c>ri$ two unit *>ges4 ,on ?is view1 e radioactive sub/ance :i* emitt$ -p>ticles mu/ give rise to helium4 ,?is at once (f]$ an explanation ( ! fact obs]v$ by ,debi]ne t act9ium z well z radium produc$ helium4 ,x 0 po9t$ out t ! pres5ce ( a d\ble *>ge ( helium-atom 0 n altoge!r improbable = reasons to be giv5 lat]4 ,:ile ! evid5ce z a :ole /rongly support$ ! view t ! -p>ticle 0 a helium atom1 x 0 f\nd exce$+ly difficult to obta9 a decisive exp]im5tal pro( ( ! relation4 ,if x c\ld be %[n exp]im5tally t ! -p>ticle did 9 reality c>ry two unit *>ges1 ! pro( ( ! relation w\ld be greatly /r5g!n$4 ,= ?is purpose an electrical me?od 0 devis$ by ,ru!r=d & ,geig] = c\nt+ directly ! -p>ticles expell$ f a radioactive sub/ance4 ,! ionization produc$ 9 a gas by a s+le -p>ticle is exce$+ly small & w\ld be difficult to detect electrically except by a v ref9$ me?od4 ,rec\rse 0 _h to an automatic me?od ( magnify+ ! ionization produc$ by an -p>ticle4 ,= ?is purpose x 0 arrang$ t ! -p>ticles %\ld be fir$ ?r\gh a small op5+ into a vessel conta9+ air or o!r gas at a l[ pressure1 expos$ to an electric field ne> ! sp>k+ value4 ,"u ^! conditions ! ions produc$ by ! passage ( ! -p>ticle ?r\gh ! gas g5]ate a l>ge numb] ( fre% ions by collision4 ,9 ?is way x 0 f\nd possible to magnify ! electrical effect due to an -p>ticle sev]al ?\s& times4 ,! entrance ( an -p>ticle into ! te/+ vessel 0 !n indicat$ by a sudd5 deflection ( ! electromet] ne$le4 ,?is me?od 0 develop$ into an accurate me?od ( c\nt+ ! numb] ( -p>ticles fir$ 9 a kn[n "t ?r\gh ! small ap]ture ( ! te/+ vessel4 ,f ?is 0 d$uc$ ! total numb] ( -p>ticles expell$ p] second f any ?9 film ( radioactive matt]4 ,9 ?is way x 0 %[n t #c4d x #ajaj -p>ticles are expell$ p] second f "o gram ( radium itself & f ea* ( its -ray products 9 equilibrium ) x4 ,! correctness ( ?is me?od 0 indicat$ by ano!r1 q di/9ct me?od ( c\nt+4 ,sir ,william ,crookes & ,el/] & ,geitel _h %[n t ! -p>ticles fall+ on a scre5 ( phosphoresc5t z9c sulphide produc$ a numb] ( sc9tillations4 ,us+ specially prep>$ scre5s1 ,ru!r=d & ,geig] c\nt$ ! numb] ( ^! sc9tillations p] second ) ! aid ( a microscope4 ,x 0 f\nd t1 )9 ! limit ( exp]im5tal error1 ! numb] ( sc9tillations p] second on a scre5 agre$ ) ! numb] ( -p>ticles imp++ on x1 c\nt$ by ! electrical me?od4 ,x 0 ?us cle> t ea* -p>ticle produc$ a visible sc9tillation on ! scre51 & t ei!r ! electrical or ! optical me?od c\ld be us$ = c\nt+ ! -p>ticles4 ,ap>t f ! purpose = :i* ^! exp]im5ts 7 made1 ! results are ( great int]e/ & importance1 = x is ! fir/ "t t x has be5 f\nd possible to detect a s+le atom ( matt] by its electrical & optical effect4 ,?is is ( c\rse only possible because ( ! great velocity ( ! -p>ticle4 ,kn[+ ! numb] ( -p>ticles expell$ f radium f ! c\nt+ exp]im5t1 ! *>ge c>ri$ by ea* -p>ticle 0 det]m9$ by measur+ ! total positive *>ge c>ri$ by all ! -p>ticles expell$4 ,x 0 f\nd t ea* -p>ticle c>ri$ a positive *>ge ( #i4c x #aj-aj electro/atic units4 ,f a consid]ation ( ! exp]im5tal evid5ce ( ! *>ge c>ri$ by ! ions 9 gases1 x 0 conclud$ t ! -p>ticle did c>ry two unit *>ges1 & t ! unit *>ge c>ri$ by ! hydrog5 atom 0 equal to #d4fe x #aj-aj units4 ,f a comp>ison ( ! kn[n value ( e_/m = ! -p>ticle ) t ( ! hydrog5 atom1 x foll[s t an -p>ticle is a project$ atom ( helium c>ry+ two *>ges1 or1 to express x 9 ano!r way1 ! -p>ticle1 aft] its *>ge is neutraliz$1 is a helium atom4 ,! data obta9$ f ! c\nt+ exp]im5ts all[ u to calculate simply ! magnitude ( a numb] ( important radioactive quantities4 ,x 0 f\nd t ! calculat$ values ( ! life ( radium1 ( ! volume ( ! emanation1 & ( ! heat+ effect ( radium 7 9 excell5t agreem5t ) ! values f\nd exp]im5tally4 ,a te/ ( ! correctness ( ^! me?ods ( calculation 0 =?com+ %ortly aft] ! publication ( ^! results4 ,ru!r=d & ,geig] calculat$1 on ! assumption t ! -p>ticle 0 a helium atom1 t "o gram ( radium 9 equilibrium %\ld produce a volume ( #aeh cubic millimetres ( helium p] ye>4 ,sir ,james ,dew> 9 #aijh c>ri$ out a long exp]im5tal inve/igation on ! rate ( production ( helium by radium1 & %[$ t "o gram ( radium 9 equilibrium produc$ ab\t #acd cubic millimetres p] ye>4 ,consid]+ ! difficulty ( ! inve/igation1 ! agreem5t betwe5 ! exp]im5tal & calculat$ values is v good & is /rong evid5ce 9 support ( ! id5tity ( ! -p>ticle ) a helium atom4 ,:ile ! :ole tra9 ( evid5ce we h consid]$ indicates ) little room = d\bt t ! -p>ticle is a project$ helium atom1 !re 0 /ill want+ a decisive & incontrov]tible pro( ( ! relation%ip4 ,x might be argu$1 = example1 t ! helium atom appe>$ z a result ( ! dis9tegration ( ! radium atom 9 ! same way z ! atom ( ! emanation & _h no direct connection ) ! -p>ticle4 ,if "o helium atom 7 lib]at$ at ! same "t t an -p>ticle 0 expell$1 exp]im5t & calculation might /ill agree & yet ! -p>ticle might be an atom ( hydrog5 or ( "s unkn[n sub/ance4 ,9 ord] to remove ?is possible objection1 x is necess>y to %[ t ! -p>ticles1 collect$ q indep5d5tly ( ! active matt] f :i* !y are expell$1 give rise to helium4 ,) ?is purpose 9 view "s exp]im5ts 7 rec5tly 7#aijh7 made by ,ru!r=d & ,royds4 ,a l>ge quantity ( emanation 0 =c$ into a glass tube :i* _h walls s ?9 t ! -p>ticles 7 fir$ "r ?r\gh !m1 ?\gh ! walls 7 imp]vi\s to ! emanation itself4 ,! -p>ticles 7 project$ into ! glass walls ( an out] seal$ vessel & 7 gradually releas$ into ! exhau/$ space betwe5 ! emanation tube & ! out] vessel4 ,aft] "s days a bright spectrum ( helium 0 obs]v$ 9 ! out] vessel4 ,!re is1 h[ev]1 "o objection to ?is exp]im5t4 ,x might be possible t ! helium obs]v$ _h diffus$ ?r\gh ! ?9 glass walls f ! emanation4 ,?is objection 0 remov$ by %[+ t no trace ( helium appe>$1 :5 ! emanation 0 replac$ by a l>g] volume ( helium itself4 ,we may ?us confid5tly conclude t ! -p>ticles !mselves give rise to helium1 & are atoms ( helium4 ,fur!r exp]im5ts %[$ t :5 ! -p>ticles 7 fir$ ?r\gh ! glass walls into a ?9 %eet ( lead or t91 helium c\ld always be obta9$ f ! metals aft] a few h\rs' bomb>dm5t4 ,consid]+ ! evid5ce toge!r1 we conclude t ! -p>ticle is a project$ atom ( helium1 :i* has1 or 9 "s way dur+ its flight acquires1 two unit *>ges ( positive electricity4 ,x is some:at unexpect$ t ! atom ( a monatomic gas l helium %\ld c>ry a d\ble *>ge4 ,x mu/ n h[ev] be =gott5 t ! -p>ticle is releas$ at a high spe$ z a result ( an int5se atomic explosion1 & plunges ?r\gh ! molecules ( matt] 9 its pa?4 ,su* conditions are exceptionably fav\rable to ! release ( loosely atta*$ electrons f ! atomic sy/em4 ,if ! -p>ticle c lose two electrons 9 ?is way1 ! d\ble positive *>ge is expla9$4 ,we h se5 t !re is e reason to believe t ! -p>ticles1 s freely expell$ f ! great majority ( radioactive sub/ances1 are id5tical 9 mass & con/itution & mu/ consi/ ( atoms ( helium4 ,we are consequ5tly driv5 to ! conclusion t ! atoms ( ! prim>y radioactive elem5ts l uranium & ?orium mu/ be built up 9 "p at lea/ ( atoms ( helium4 ,^! atoms are releas$ at def9ite /ages ( ! trans=mations at a rate indep5d5t ( control by laboratory =ces4 ,!re is good reason to believe t 9 ! majority ( cases1 a s+le helium atom is expell$ dur+ ! atomic explosion4 ,?is is c]ta9ly ! case = radium itself & its s]ies ( products4 ,on ! o!r h&1 ,bronson has drawn att5tion to c]ta9 cases1 viz4 ! emanations ( act9ium & ( ?orium1 :]e app>5tly two & ?ree atoms ( helium respectively are expell$ at "o "t4 ,no d\bt ^! exceptions w receive c>eful inve/igation 9 ! future4 ,x is ( int]e/ to note t uranium itself appe>s to expel two -p>ticles = "o f ea* ( its products4 ,kn[+ ! numb] ( atoms ( helium expell$ f ! atom ( ea* product1 we c at once calculate ! atomic weights ( ! products4 ,= example1 9 ! uranium-ionium-radium s]ies1 uranium expels two -p>ticles & ea* ( ! six foll[+ -ray products "o1 i4e4 eight 9 all4 ,tak+ ! atomic weight ( uranium z #bch4e1 ! atomic weight ( ionium %\ld be #bcj4e1 ( radium #bbf4e1 ( ! emanation #bbb4e1 & s on4 ,x is ( int]e/ to note t ! atomic weight ( radium d$uc$ 9 ?is way is 9 close agreem5t ) ! late/ exp]im5tal values4 ,! atomic weight ( ! end-product ( radium1 result+ f ! trans=mation ( radium ,f 7polonium7 %\ld be #bch4e - #h x #d #bjf4e1 or a value close to t = lead4 ,long ago1 ,boltwood sugge/$ f exam9ation ( analyses ( old uranium m9]als1 t lead 0 9 all probability a trans=mation product ( ! uranium-radium s]ies4 ,! co9cid5ce ( numb]s is c]ta9ly /rik+1 b a direct pro( ( ! production ( lead f radium w be requir$ be=e ?is conclusion c be consid]$ z def9itely e/abli%$4 ,x is v rem>kable t a *emically in]t elem5t l helium %\ld play su* a prom95t "p 9 ! con/itution ( ! atomic sy/ems ( uranium & ?orium & radium4 ,x may well be t ?is prop]ty ( helium ( =m+ complex atoms is 9 "s way connect$ ) its inability to ent] into ord9>y *emical comb9ations4 ,x mu/ n be =gott5 t uranium & ?orium & ea* ( _! trans=mation products mu/ be reg>d$ z di/9ct *emical elem5ts 9 ! ord9>y s5se4 ,!y diff] f ord9>y elem5ts 9 ! comp>ative in/ability ( _! atomic sy/ems4 ,! atoms break up spontane\sly ) great viol5ce1 expell+ 9 _m cases an atom ( helium at a high spe$4 ,all ! evid5ce is aga9/ ! view t uranium or ?orium or radium c be reg>d$ z an ord9>y molecul> comp\nd ( helium ) "s kn[n or unkn[n elem5t1 :i* breaks up into helium4 ,! "* ( ! radioactive trans=mations & _! indep5d5ce ( temp]ature & o!r ag5cies h no analogy 9 ord9>y *emical *anges4 ,ap>t f _! radioactivity & high atomic weight1 uranium1 ?orium1 & radium %[ no specially di/9ctive *emical behavi\r4 ,radium = example is closely alli$ 9 g5]al *emical prop]ties to b>ium4 ,x is consequ5tly n unreasonable to suppose t o!r elem5ts may be built up 9 "p ( helium1 al?\gh ! abs5ce ( radioactivity may prev5t u f obta9+ any def9ite pro(4 ,on ?is view1 x may prove significant t ! atomic weights ( _m elem5ts diff] by f\r--! atomic weight ( helium--or a multiple ( f\r4 ,"t is too limit$ to discuss 9 great] detail ^! & o!r int]e/+ que/ions :i* h be5 rais$ by ! pro( ( ! *emical nature ( ! -p>ticle4 ,footnote #a3 ,e4 ,ru!r=d1 ,uranium radiation & ! electrical conduction produc$ by x1 ,phil4 ,mag41 #dg 7#ahii7 #aaf4 ,footnote #b3 ,e4 ,ru!r=d & ,f4 ,soddy1 ,phil4 ,mag41 #e 7#aijc71 #ajf4 ,footnote #c3 ,e4 ,ru!r=d & ,f4 ,soddy1 ,phil4 ,mag41 #d 7#aijb71 #ehb4 ,footnote #d3 ,e4 ,ru!r=d & ,f4 ,soddy1 ,phil4 ,mag41 #e 7#aijc71 #dec4 ,footnote #e3 ,e4 ,ru!r=d1 lett] 9 ,nature1 #fi 7,aug4 #bj1 #aijc74