Piotr Leonidovich Kapitza, 9 July 1894 8 April 1984
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- * In England, the Russian Piotr was at first rendered as Pierre but he was usually known as Peter.
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April 1984 Piotr Leonidovich Kapitza, 9 July 1894 - 8 D. Shoenberg, F. R. S. 1985 , 326-374, published 1 November 31 1985
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P I O T R L E O N ID O V IC H K A P IT Z A 9 J u ly 1894 — 8 A p r il 1984 E le c te d F .R .S . 1929
D .
S h o e n b e r g , F .R .S . R u s s i a , 1 8 9 4 -1 9 2 1 P e t e r K a p i t z a * w a s a le g e n d a ry fig u re b o th in R u t h e r f o r d ’s C a m b rid g e o f th e 19 2 0 s a n d 19 30 s a n d s u b s e q u e n tly in M o s c o w to th e e n d o f h is lo n g life a n d th e le g e n d s se rv e to illu s tr a te h is c o lo u rfu l p e rs o n a lity . I n h is s c ie n tific w o rk h e s h o w e d g r e a t v e rs a tility a n d b r o u g h t th e sk ills o f an e n g in e e r a n d m a th e m a tic ia n to b e a r o n im p o r ta n t p r o b le m s in p h y s ic s a n d te c h n o lo g y in a n e n tir e ly o rig in a l w ay . H e also h a d b r o a d c u ltu r a l a n d so cial in te r e s ts a n d h is o rig in a l id e a s o n sc ie n tific e d u c a tio n a n d o r g a n iz a tio n h a v e h a d a p r o f o u n d in flu e n c e , p a rtic u la rly o n th e d e v e lo p m e n t o f S o v ie t p h y s ic s . H e w a s b o r n in K r o n s ta d t, th e is la n d fo rtre s s o n th e N e v a n e a r S t P e te rsb u rg ,'} ' in to a fa m ily w ith s tr o n g in te lle c tu a l tr a d itio n s . H is fa th e r, C o lo n e l (la te r G e n e ra l) L e o n id P e tro v ic h K a p itz a w as a m ilita ry e n g in e e r in v o lv e d in m o d e r n iz in g th e fo rtific a tio n s o f K r o n s ta d t. T h e K a p itz a s h a d b e e n la n d e d g e n tr y w ith P o lis h a n te c e d e n ts a n d th e fa m ily w as w ell r e p r e s e n te d in th e p ro fe s s io n s . H is m o th e r , O lg a I e r o n im o v n a , to w h o m h e w as v e ry clo se u n til h e r d e a th in 1937, w as a s p e c ia lis t in c h il d r e n ’s lite r a tu r e a n d fo lk lo re a n d an im p o r ta n t fig u re in th e lite r a ry w o rld o f S t P e te r s b u r g . S h e o rg a n iz e d a c lu b fo r y o u n g w r ite r s , m a n y o f w h o m s u b s e q u e n tly b e c a m e fa m o u s . H e r fa th e r, G e n e r a l I e r o n im Iv a n o v ic h S te b n its k i, also p a rtly o f P o lis h o rig in a n d a m ilita ry e n g in e e r s p e c ia liz in g in c a r to g ra p h y , w as a g e o g ra p h e r o f in te r n a tio n a l r e p u te , a c o rr e s p o n d in g m e m b e r o f th e I m p e r ia l A c a d e m y o f S c ien c e s a n d an a r d e n t tra v e lle r all o v e r th e w o rld ; it is p e r h a p s fro m h im th a t P e te r K a p itz a in h e r ite d h is o w n love o f tra v e l. M u c h o f S te b n its k i’s m ilita ry se rv ic e w as in th e C a u c a s u s , w h e re h e p e rs o n a lly m a p p e d o u t th e im p o r ta n t m o u n ta in * In England, the Russian Piotr was at first rendered as Pierre but he was usually known as Peter. T he transliteration of his surname is the one he used himself, but the tz is often rendered as ts. t After 1914 St Petersburg became Petrograd and after 1924 Leningrad. 327
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328 Biographical Memoirs peaks a n d m ad e g ra v ita tio n a l m e a s u re m e n ts ; later he w as h ead o f th e M ilita ry T o p o g ra p h ic a l D e p a r tm e n t of th e Im p e ria l G e n e ra l S ta ff in S t P e te rs b u rg . U n u s u a lly for his tim e, he a rra n g e d for his d a u g h te rs to have a h ig h e r e d u c a tio n , O lga in th e h u m a n itie s a n d A le x a n d ra in m a th e m a tic s an d science. A le x a n d ra p lay ed an im p o rta n t p a rt in P e te r ’s u p b rin g in g fo r it w as she w ho d isc o v e red , r a th e r to th e s u rp rise o f th e fam ily, th a t he h a d an u n u s u a lly q u ick g rasp o f a rith m e tic . T h o u g h a lively bo y, he h a d seem ed a b it b a c k w a rd in so m e o th e r resp e c ts. H e n e v e r o v e rc a m e a c e rta in in d is tin c tn e s s a n d slo p p in e ss in sp e ec h a n d n e v e r le a rn e d to spell p ro p e rly in any lan g u a g e — a c o n sid e ra b le h a n d ic a p in his early career. H e w as a d m itte d to th e ‘classical g y m n a s iu m ’, w h ich sp ecialized in th e h u m a n itie s , b u t h a d to leave th is school in 1906 at th e e n d o f his first y ear b ec au se of in a d e q u a te p ro g re ss an d tra n s fe rre d to th e m o re scien tifically o rie n te d ‘re a ls c h u le ’. H e en jo y e d a k in d o f rev en g e 70 years la te r w h e n , to m ark his seco n d aw ard o f th e title H e ro o f S o cialist L a b o u r, his b u s t w as e re c te d in a p u b lic sq u a re o f K ro n s ta d t o p p o site th e g y m n a siu m fro m w hich he h a d b een excluded! A lth o u g h th is e x clu sio n e v id e n tly ra n k le d , th e ‘re a ls c h u le ’ w as m u c h m o re a p p ro p ria te fo r d e v e lo p in g his ta le n ts, an d in 1912 he g ra d u a te d w ith h o n o u rs a n d e n te re d th e e le c tro te c h n ic a l facu lty of th e S t P e te rs b u rg P o ly te c h n ic a l I n s titu te — fo r lack o f L a tin an d G re e k he w as n o t elig ib le to e n te r th e S t P e te rs b u rg U n iv e rs ity , th e n reg a rd e d as th e m o re p re stig io u s in s titu tio n . H is stu d ie s w ere in te r ru p te d by th e 1914 w ar a n d fo r tw o years K a p itz a w as an a m b u la n c e d riv e r at th e P o lish fro n t. A fte r d e m o b iliz a tio n he r e tu rn e d to th e P o ly te c h n ic a l I n s titu te w h e re he g ra d u a te d in 1918 an d w as a p p o in te d to a te a c h in g p o st in th e In s titu te , w h ic h he h e ld u n til he m o v ed to C a m b rid g e in 1921. D u rin g th ese y ears th e m o v in g s p irit in th e p h y sics w o rld of P e tro g ra d , a n d in d ee d o f R u ssia, w as A. F . Joffe, w ho w as actively d e v e lo p in g a p h y sics school w ith an o u tlo o k m o re m o d e rn th a n h a d b e e n tra d itio n a l in R u ssia u p to th e n , an d w ith an e m p h a sis on rese a rc h an d se m in a rs to keep a b re a st of d e v e lo p m e n ts in th e W est. A fter 1918 th e rese a rc h effort w as c o n c e n tra te d in th e new ly e sta b lish e d P e tro g ra d P h y sic o -te c h n ic a l In s titu te , w h e re Joffe su cceed ed in c o lle ct ing a g ro u p of y o u n g an d e n th u s ia stic sc ie n tists a ro u n d h im w ho fo rm e d the n u c le u s o f th e e n o rm o u s g ro w th of S oviet p h y sics in later years. T h e c re a tio n o f th is new in s titu te for p h y sics rese a rc h m u st have seem ed w ildly v isio n ary at th a t tim e since, a fte r th e chaos of th e w ar a n d th e upheaval of th e R e v o lu tio n , th e e co n o m y o f th e c o u n try w as in a d isa stro u s state. T h e r e w ere g rea t sh o rta g e s o f food a n d fuel and p ractically no scientific e q u ip m e n t, so th a t rese a rc h co u ld be d o n e only on a ‘do it y o u rse lf’ basis. In sp ite of these difficulties, h o w ev er, q u ite a lot got sta rte d . K a p itz a took u p several p ro je c ts of to p ical in te re st. O ne w as th e m e a su re m e n t of th e a n g u la r m o m e n tu m associated w ith m ag n e tiz a tio n of on November 29, 2017 http://rsbm.royalsocietypublishing.org/ Downloaded from
Piotr Leonidovich K a p itza 329
m a tte r, a n d h is first scien tific p a p e r* w as a c ritic a l review ( l ) f o f th e e x p e rim e n ts b y E in s te in a n d de H a a s, w ho h a d d e m o n s tra te d th e effect in 1915, a n d b y B a rn e tt w h o a lm o st sim u lta n e o u sly d e m o n s tra te d th e in v erse effect. A t th a t tim e th e re a p p e a re d to be a c o n tra d ic tio n b e tw e e n th e tw o sets o f e x p e rim e n ts a n d K a p itz a c o n c lu d e d th a t th e re m u s t be som e e rr o r in B a r n e tt’s e x p e rim e n t b ec au se it gave o nly h a lf th e classically e x p e c te d ratio of a n g u la r m o m e n tu m to m a g n e tiz a tio n . H o w e v e r, so o n a fte rw a rd s , E in s te in an d de H aas d isc o v e red an e rro r in th e ir e x p e rim e n t a n d c o n firm e d B a r n e tt’s ‘a n o m a lo u s ’ re su lt w h ic h w as la te r e x p la in e d in te rm s o f e le c tro n sp in . A se co n d p a p e r (2) d e scrib es an in g e n io u s im p ro v e m e n t in th e te c h n iq u e o f p re p a rin g W o lla sto n fibres; K a p itz a also b ecam e a d e p t at u sin g B o y s’s b o w a n d a rro w m e th o d of p ro d u c in g v ery fine q u a rtz fibres. A n o th e r line of w o rk w as th e stu d y o f a to m ic and m o le c u la r b e a m s an d to g e th e r w ith his frie n d S e m en o v , K a p itz a p ro p o se d a te c h n iq u e for m e a s u rin g a to m ic m a g n e tic m o m e n ts b y o b se rv in g th e s p re a d o f an a to m ic b e a m a fte r p a ssin g th ro u g h a stro n g ly in h o m o g e n e o u s m ag n e tic field (6). A lth o u g h th e ir p a p e r m e n tio n s th a t ‘e x p e rim e n ts in th is d ire c tio n have a lre ad y b e g u n ’ n o th in g f u r th e r w as p u b lis h e d . In fact b e tw e e n th e tim e o f s u b m issio n o f th e p a p e r in D e c e m b e r 1920 a n d its p u b lic a tio n in 1922, S te rn an d G e rla c h h a d n o t o nly p ro p o se d essen tially th e sam e id ea, b u t c a rrie d it o u t in p rac tic e (S te rn 1921, G e rla c h & S te rn 1921, 1922), a n d so p ro v id e d th e d e m o n s tra tio n o f sp atial q u a n tiz a tio n fo r w h ic h m an y years late r S te rn w as aw a rd ed a N o b e l prize. A th ir d field to w h ic h K a p itz a c o n trib u te d w as th a t o f X -ra y s a n d his p ro p o sa l (3) to focus a b ro a d b e a m o f X -ra y s b y a b e n t cry sta l seem s to have a n tic ip a te d w h a t m u c h la te r becam e an im p o rta n t p rac tic a l te c h n iq u e . Jo h a n sso n (1933) d e s c rib e d th e first p rac tic a l rea liz a tio n o f th is idea, b u t does n o t a p p e a r to have b een aw are o f K a p itz a ’s p a p e r. S o o n a fte r K a p itz a w as d e m o b iliz e d , an d follow ing a ro m a n tic trip to H a rb in in C h in a , he m a rrie d N a d e z h d a K y rillo v n a , d a u g h te r o f G e n e ral C h e rn o sv ito v , an d a son, Ie ro n im , w as b o rn in 1917. A second ch ild was e x p e cte d to w a rd s th e e n d o f 1919 b u t d isa ste r stru c k th e fam ily. In th e te rrib le c o n d itio n s follow ing th e R ev o lu tio n an d th e C ivil W ar, e p id e m ic s w ere rife an d Ie ro n im c a u g h t scarlet fever an d d ied. N a d e z h d a w as q u ite stru c k d o w n by th is blow a n d soon a fter she h a d given b irth to a d a u g h te r (also called N a d e z h d a ), b o th su c c u m b e d to th e S p a n ish in fluenza th a t w as th e n rag in g in th e city. O n to p of th is, K a p itz a ’s fa th e r also d ied o f ’flu at a b o u t th e sam e tim e. K a p itz a , w ho h ad h im se lf h ad a b a d b o u t o f ’flu, w as o v e rw h e lm ed by th ese trag ic losses an d for a tim e w as u n a b le to w ork. H is frie n d s w o n d e re d w h a t co u ld be do n e to help * T h is w as in fact n o t h is first p u b lic a tio n . H e h a d a lre a d y p u b lis h e d a p o p u la r a rtic le ( G l ) a b o u t th e p r o d u c tio n o f co d liv e r oil, b a s e d on h is tra v e ls in th e fa r N o r th o f R u ssia , a n d illu s tra te d b y his o w n p h o to g r a p h s . t N u m b e r s g iv en in th is fo rm re fe r to e n trie s in th e b ib lio g ra p h y at th e e n d o f th e te x t. on November 29, 2017 http://rsbm.royalsocietypublishing.org/ Downloaded from 330 Biographical Memoirs h im fo rg e t his u n h a p p y s itu a tio n a n d s o m e th in g tu rn e d u p th a t n o t on ly d is tra c te d K a p itz a fro m his g rief, b u t, as it tu r n e d o u t, c o m p le te ly c h a n g e d th e c o u rse o f his life. T h is w as th e se ttin g u p , at Jo ffe ’s p ro m p tin g , o f a ‘C o m m issio n of th e R u ssian A c a d e m y o f S ciences fo r re n e w in g scientific re la tio n s w ith o th e r c o u n tr ie s ’, w h ich w as lib e rally p ro v id e d w ith fo re ig n c u rre n c y to b u y e q u ip m e n t a b ro a d (see S o m in sk ii 1965, K ry lo v 1984). B esides Joffe, an im p o rta n t m e m b e r o f th e c o m m issio n w as A d m ira l A. N . K ry lo v , th e w ell k n o w n naval e n g in e e r a n d a p p lie d m a th e m a tic ia n , w ho w as late r to b e co m e K a p itz a ’s se co n d fa th e r-in -la w . B o th h a d a h ig h o p in io n of K a p itz a ’s scientific g ifts a n d w a n te d to h e lp in his difficult p e rso n a l situ a tio n ; a p p o in tin g h im to jo in th e c o m m issio n seem ed an ideal so lu tio n . T ra v e l a b ro a d at th a t tim e was c o m p lic a te d b ecau se m o st o f th e o u tsid e w o rld h ad no d ip lo m a tic re la tio n s w ith S oviet R ussia. Joffe set o u t in F e b ru a ry 1921, a n d as soon as he got to B erlin b eg an try in g to g et a visa for K a p itz a , w hile he a n d o th e r m e m b e rs o f th e c o m m issio n w ere o c c u p ie d w ith b u y in g e q u ip m e n t. G e rm a n y , F ra n c e a n d H o lla n d d id n o t w a n t to risk a d m ittin g so m eo n e w ho m ig h t p ro v e to be a y o u n g c o m m u n is t a g ita to r, b u t E n g la n d w as m o re a c c o m m o d a tin g a n d e v e n tu ally in M ay , Joffe su c ce e d e d in g e ttin g K a p itz a an E n g lish visa. A t last, late in M ay , K a p itz a a rriv e d in E n g la n d b y sh ip an d early in J u n e he a n d Joffe s ta rte d a ro u n d o f scientific visits, w h ic h c u lm in a te d in a v isit to R u th e rfo rd in C a m b rid g e on 12 Ju ly . T h e y w ere receiv ed very co rd ially by R u th e rfo rd b u t w h e n K a p itz a asked if he m ig h t w o rk in th e C a v e n d ish fo r a few m o n th s R u th e rfo rd w as r a th e r d isc o u ra g in g , say ing th e L a b o ra to ry was alre ad y c ro w d e d an d it w o u ld be difficult to a c c o m m o d a te one m o re. R u th e rfo rd w as r a th e r tak e n aback w h e n K a p itz a re p lie d by asking w h a t a ccu racy he aim e d at in his e x p e rim e n ts. T h e a n sw e r to th is seem in g ly irre le v a n t q u e s tio n w as 2 o r 3% an d K a p itz a th e n p o in te d o u t th a t as th e re w ere a b o u t 30 re se a rc h e rs in th e C a v e n d ish , one m o re w o u ld h a rd ly be n o tic e d b ecau se he w o u ld com e w ith in th e e x p e rim e n ta l erro r! T h is in g en io u s a p p ro a c h p e rs u a d e d R u th e rfo rd to a d m it K a p itz a a fte r all. A s a p o s ts c rip t it m ay be m e n tio n e d th a t a year late r K a p itz a asked R u th e rfo rd w h y he h a d agreed to take h im on an d R u th e rfo rd la u g h e d a n d said ‘I c a n ’t th in k w hy, b u t F m very glad th a t I d id ’.
1921-3 4
K a p itz a jo in e d th e C a v e n d ish in Ju ly 1921 a n d a lth o u g h th e o rig inal p lan w as for h im to stay only o v er th e w in te r he re m a in e d fo r 13 years. H is in tro d u c tio n to C a m b rid g e life an d his im p re ssio n s o f R u th e rfo rd an d th e C a v e n d ish are v ividly d e sc rib e d in the le tte rs he w ro te at fre q u e n t in te rv als to his m o th e r in P e tro g ra d (q u o te d in D a n in 1966, P a rry 1968 on November 29, 2017 http://rsbm.royalsocietypublishing.org/ Downloaded from Piotr Leonidovich K a p itza 331
a n d R u b in in 1 9 8 5 ).# T h e u su a l in itia tio n o f n ew re se a rc h s tu d e n ts w as a m o n th o r tw o o f p ra c tic a l w o rk in th e C a v e n d ish a ttic o n v a rio u s re le v a n t te c h n iq u e s u n d e r C h a d w ic k ’s su p e rv is io n a n d a few days a fte r his a rriv al K a p itz a w ro te (24 Ju ly ) ‘F o r th e tim e b e in g . . . I am w o rk in g o n ly at m y p ra c tic a l co u rse ; as to th e fu tu re , I d o n ’t k n o w . . . . T im e w ill show . . . .’ In fact h is skill a n d a ssid u ity w e re su c h th a t C h a d w ic k w as satisfied a fte r o n ly tw o w eeks a n d b y early A u g u s t K a p itz a h a d at R u th e r f o r d ’s s u g g e stio n c h o se n to stu d y ho w th e e n e rg y o f an a -p a r tic le falls off to w a rd s th e e n d o f its ran g e . P re v io u s ly th is h a d b e e n m e a s u re d by o b s e rv in g th e d e fle ctio n o f th e a -p a r tic le in a m a g n e tic field, b u t th e lim ita tio n o f th is m e th o d w as th a t p a rtic le s o f low e n e rg y c o u ld n o t be d e te c te d . K a p itz a ’s m e th o d w as to m e a su re th e e n e rg y in a c o llim a te d b e a m o f a -p a r tic le s b y th e h e a tin g it p ro d u c e d in a p la te a tta c h e d to a B oys ra d io m ic ro m e te r. T h is p ro je c t w as b ro u g h t to a successfu l c o n c lu sion w ith a m a z in g ra p id ity . W ith in n in e m o n th s o f th e c o n c e p tio n o f th e idea he w as a lre ad y d ra ftin g a p a p e r fo r p u b lic a tio n a n d b y m id - J u n e th e p a p e r w as se n t off. O n 19 J u n e 1922 he w ro te to his m o th e r: ‘T o d a y th e C ro c o d ile s u m m o n e d m e tw ice a b o u t m y m a n u s c rip t. . . . I t w ill be p u b lis h e d in th e P ro c e e d in g s o f th e R oyal S o ciety , w h ic h is th e g re a te s t h o n o u r a piece o f re se a rc h can achieve h e re . . . . O n ly n o w have I really e n te re d th e C ro c o d ile ’s school . . . w h ic h is c e rta in ly th e m o st a d v a n ce d school in th e w o rld a n d R u th e rf o r d is th e g re a te st p h y sic ist a n d o rg a n ise r. I t is o nly n o w th a t I have felt m y s tre n g th . S u ccess gives m e w ings a n d I am c a rrie d aw ay b y m y w o rk .’ ‘C ro c o d ile ’ w as a n ic k n a m e K a p itz a in v e n te d for R u th e rfo rd early on an d m a n y y ears la te r he to ld R itc h ie C a ld e r (1951, p. 66): ‘In R u ssia th e c ro co d ile is th e sy m b o l for th e fa th e r o f th e fam ily a n d is also reg a rd e d w ith awe an d a d m ira tio n b ecau se it has a stiff n eck an d c a n n o t tu r n back. It ju s t goes s tra ig h t fo rw ard w ith g ap in g ja w s — like science, like R u th e r f o r d .’ A m o re fan cifu l b u t p ro b a b ly e n tire ly a p o c ry p h a l v ersio n , p o p u la r in th e C a v e n d ish , w as th a t it w as a fte r th e cro co d ile in P e te r P a n th a t sw allow ed an a la rm clock to give ad v ance w a rn in g of its so m ew h at frig h te n in g a p p e ara n ce . T h is v e rsio n finds som e slig h t s u p p o rt in an early le tte r (12 O c to b e r 1921): ‘R u th e rfo rd g reets m e in creasin g ly p lea sa n tly a n d asks how th in g s are g o ing w h en he sees m e. B u t I am a little afraid o f h im . I w ork alm o st n e x t d o o r to his office. T h is is b ad since I have to be very * * A m o re c o m p le te e d itio n o f th e s e a n d o th e r le tte rs is b e in g p re p a r e d b y M r s A. A. K a p itz a . T h e q u o ta tio n s in th is m e m o ir are m y o w n r a th e r fre e tr a n s la tio n s fro m th e R u ssia n . on November 29, 2017 http://rsbm.royalsocietypublishing.org/ Downloaded from 332 Biographical Memoirs c a re fu l w ith m y sm o k in g: its a m is fo rtu n e if he sh o u ld c a tc h you w ith a p ip e in y o u r m o u th . B u t th a n k G o d he has a h eavy tre a d a n d I can reco g n ize his fo o tste p s . . T h e p u b lis h e d p a p e r (7) sh o w s th a t K a p itz a ’s e n th u s ia sm a b o u t his e x p e rim e n t w as in d ee d ju stifie d . B oys (1923) said of his ra d io m ic ro m e te r th a t ‘its e x tre m e d elicacy of c o n s tru c tio n re q u ire s m o re th a n o rd in a ry skill on th e p a rt of th e u s e r ’ a n d K a p itz a n o t o nly d e m o n s tra te d th is skill an d e x p lo ite d his e x p e rien c e o f fine q u a rtz fibres b u t in c o rp o ra te d m an y in g en io u s fea tu re s to avoid v a rio u s stra y effects th a t in his p re lim in a ry e x p e rim e n ts c o m p le te ly sw a m p ed th e g e n u in e sm all h e a tin g effect o f th e a -p a rtic le s . H e w ro te to his m o th e r (4 D e c e m b e r 1921) th a t ‘. . . [his device] is so sen sitiv e th a t it can d e te c t th e flam e o f a can d le 2 v e rsts [ro u g h ly 2 km ] aw ay a n d re s p o n d to a te m p e ra tu re rise o f a m illio n th o f a degree! . . .’. H is re su lts c o n v in c in g ly sh o w ed th a t th e e n e rg y fell steep ly to a n eg lig ib le value to w a rd s th e e n d of th e a -p a rtic le range. T h is p u b lic a tio n illu s tra te s several c h a ra c te ris tic fea tu re s o f m u c h of K a p itz a ’s late r w ork: his ab ility to w ork o u t in p ra c tic e r a th e r c o m p lic a te d sch em es d e sig n e d to give e x tre m e se n sitiv ity , his th o ro u g h g rasp of p o te n tia l p itfalls, his sp eed o f w o rk in g a n d his th o ro u g h n e s s in in te rp re ta tio n . A n o th e r in te re s tin g fe a tu re is K a p itz a ’s fo n d n e ss for re g a rd in g each p ro je c t as p a rt o f a la rg e r g ro u p o f in v e stig a tio n s, b u t th e n g e ttin g e x cited by a new idea a n d fo rg e ttin g a b o u t c o n tin u in g th e o rig in al p lan. T h u s th e p a p e r is d e sc rib e d as ‘P a rt I ’ a n d th e a b s tra c t m e n tio n s th a t fu rth e r w ork will be d e sc rib e d in a n o th e r p a p e r. H o w e v e r no P a rt II ever a p p e a re d , p ro b a b ly b ecau se K a p itz a h a d b e co m e c o m p le te ly e n gro ssed by a new idea th a t cam e u p at th a t tim e. T h is idea w as a p o ssib le new m e th o d o f stu d y in g how th e a -p a rtic le v elocity varied alon g its tra c k by m e a s u rin g th e tra c k c u rv a tu re in a m ag n e tic field. E x istin g m a g n e ts w ere n o t cap ab le of p ro d u c in g large e n o u g h stead y fields to cu rv e th e tra c k s sufficiently, an d K a p itz a ’s novel idea w as to use fields th a t w ere m u c h larg e r b u t lasted for only a very sh o rt tim e. T h is m a rk e d a tu rn in g p o in t in K a p itz a ’s career. O n ce th e large im p u lsiv e m ag n e tic fields h a d b een ach ieved he saw w hole new vistas o p e n in g u p for e x p lo itin g th e te c h n iq u e , an d th is led h im in to p io n e e rin g w o rk in solid state a n d low te m p e ra tu re p h y sics. I t w as also the b e g in n in g of th e tra n s itio n of th e C a v e n d ish fro m th e s trin g and sealing w ax tra d itio n to th e age of large m ac h in e ph y sics. O ne o f the basic p ro b le m s o f p ro d u c in g an im p u lsiv e field is how to p ro v id e a large sto re o f en e rg y th a t can be c o n v e rte d in to electrical p o w er an d rap id ly d isc h a rg ed th ro u g h a coil. A n o b v iou s c a n d id a te for su ch an en ergy sto re w as an electrical c o n d e n se r o f large cap acity ch a rg e d to a high voltage, b u t su ch a c o n d e n se r w o u ld have b een ex p en siv e an d K a p itz a chose in stead a ch em ical sto re, essentially a large a c c u m u la to r of special desig n , w h ich he co uld b u ild him self. on November 29, 2017 http://rsbm.royalsocietypublishing.org/ Downloaded from Piotr Leonidovich K apitza 333
H e w as e n c o u ra g e d b y R u t h e r f o r d ’s re a c tio n to his idea; as he w ro te to his m o th e r (15 J u n e 1922): ‘T h e C ro c o d ile is tak e n w ith m y idea a n d th in k s it w ill su cceed . H e h as a d e v ilish feelin g fo r e x p e rim e n t a n d if he th in k s th a t so m e th in g w ill co m e o u t o f it, th a t is a v ery g o o d o m en . H is a ttitu d e to w a rd s m e gets b e tte r a n d b e tte r . . .’ H e also m e n tio n e d th a t a ‘y o u n g p h y s ic is t’ (P. M . S. B lack ett, 3 y ears his ju n io r ) w as g o in g to w o rk w ith h im . B lack ett in tro d u c e d h im to th e su b tle tie s o f th e W ilso n clo u d c h a m b e r, w h ic h w as u se d fo r rev e a lin g th e a -tra c k s , b u t th e c o lla b o ra tio n d id n o t c o n tin u e b e y o n d th e in itial stages. A few day s la te r K a p itz a w ro te o f a n o th e r sig n ifican t sign of R u th e r f o r d ’s risin g esteem : ‘T h e C ro c o d ile ’s p e rm iss io n for L a u rm a n n to com e is th e b e st d e m o n s tra tio n o f h is k in d a ttitu d e to m e .’ E m il Y an o v ich L a u rm a n n (for som e b io g ra p h ic a l d etails see S h o e n b e rg 1954) w as an E s to n ia n w ho h a d c o lla b o ra te d w ith K a p itz a in P e tro g ra d an d w as re m a rk a b ly skilled in all so rts o f te c h n iq u e s su c h as electrical e n g in e e rin g , p h o to g ra p h y an d , m o st im p o rta n tly , th e h a n d lin g o f d elicate e q u ip m e n t. H e w as a little d e a f a n d v isito rs to th e la b o ra to ry w ere o fte n s ta rtle d b y K a p itz a ’s lo u d cries o f ‘B a ro n ’ w h e n he n e e d e d L a u r m a n n ’s assistance. B aro n w as a n ick n am e b a se d on a h a lf jo k in g tra d itio n in R u ssia th a t th e B altic p ro v in c e s w ere e n tire ly p o p u la te d b y n o b ility . A lth o u g h th e n ew p ro je c t w as tec h n ica lly m u c h m o re c o m p lic a te d a n d on a la rg e r scale th a n a n y th in g K a p itz a h ad tack led b efo re, K a p itz a ’s d riv e , b ack ed by R u th e r f o r d ’s s u p p o rt a n d L a u r m a n n ’s assistan ce p r o d u c e d re su lts v ery qu ick ly . A fte r som e early failu res he w ro te on 17 A u g u st, only 2 m o n th s a fte r s ta rtin g , ‘T h e p re lim in a ry e x p e rim e n ts w ere c o m p le te ly successful. I am to ld th a t th e C ro c o d ile speaks o f n o th in g else ju s t now . I have b een giv en a large room in a d d itio n to th e one I alread y w ork in, a n d for th e full scale e x p e rim e n t I have got p e rm issio n to s p e n d a fairly su b s ta n tia l su m o f m o n e y .’ [T h is w as £150!] an d on 2 S e p te m b e r: ‘M y e x p e rim e n ts are a ssu m in g a very b ro a d scope . . . I shall re m e m b e r m y last c o n v e rsa tio n w ith R u th e rfo rd as long as I live. A fte r a w hole lot o f c o m p lim e n ts he said ‘I sh o u ld be very h a p p y if I co u ld have th e p o ssib ility of c re a tin g a special lab o ra to ry for you in w h ic h you co uld w ork w ith y o u r ow n s tu d e n ts .’ . . . A m I really such an able p erso n? I feel un easy a n d alarm ed . W ill I be able to co pe?’ A n d th e n at last, on 29 N o v e m b e r, p re su m a b ly after th e c o n stru c tio n of th e W ilso n c h a m b e r as well as th e h ig h field e q u ip m e n t: ‘. . . F o r m e to d ay is to som e e x te n t a h isto ric day . . . In fro n t of m e is a p h o to g ra p h w ith n o th in g b u t th re e cu rv e d lines on it. B ut on November 29, 2017 http://rsbm.royalsocietypublishing.org/ Downloaded from
334 Biographical Memoirs th e se th re e lines sh o w th e tra c k s o f a -p a r tic le s in a m a g n e tic field o f terrific s tre n g th . T h e s e th re e lin es have co st P ro fe s s o r R u th e rfo rd 150 p o u n d s ste rlin g a n d h av e co st m e a n d E m il Y a n o v ic h 3 \ m o n th s o f e x tre m e ly h a rd w o rk . B u t h e re th e y are a n d e v e ry o n e in th e U n iv e rs ity is ta lk in g a b o u t th e m . S tra n g e : o n ly th re e c u rv e d lines! T h e C ro c o d ile is v ery p lea se d w ith th ese th re e c u rv e d lines. . . . M a n y p e o p le h av e co m e to look at th e se th re e c u rv e d lines an d a d m ire d th e m . N o w w e m u s t go f u rth e r a n d th e re is m u c h w o rk a h e a d .’ By M a rc h 1923, again o n ly n in e m o n th s a fte r s ta rtin g , a p a p e r h a d b e e n s u b m itte d th a t w as p u b lis h e d soon a fte r (10). T h is w as follo w ed a y ear late r, w h e n th e re se a rc h h a d b e e n c o m p le te d , by tw o f u rth e r p a p e rs (11, 12), th e first g iv in g d e ta ils o f th e im p u lsiv e field m e th o d a n d th e se co n d d e s c rib in g th e special d esig n o f th e W ilso n c h a m b e r, th e e la b o ra te sw itc h in g a n d tim in g d ev ices in v o lv e d a n d finally a d e ta ile d a c c o u n t of how th e c u rv a tu re of th e a -p a rtic le tra c k s v a rie d w ith p o sitio n alo n g th e tra c k . E ffectively th e c u rv a tu re m e a s u re d th e ratio o f v elo city to ch arg e a n d th e v a ria tio n o f th e average c h a rg e w ith p o sitio n c o u ld be d e d u c e d fro m o th e r e x p e rim e n ts a n d som e ap p eal to th e o ry . T h u s finally a g ra p h w as o b ta in e d o f v elo city a g a in st ran g e, ju s t as in th e h e a tin g e x p e rim e n t d e sc rib e d e a rlie r, a n d m u c h to K a p itz a ’s sa tisfa c tio n th e tw o ag re e d q u ite rea so n a b ly . W h ile all th is w ork w as p ro g re ssin g , K a p itz a ’s p o sitio n in C a m b rid g e w as ra p id ly b e in g c o n so lid a te d . I n J a n u a ry 1923 he w as officially a d m itte d as a rese a rc h s tu d e n t fo r th e P h .D . d eg ree, w ith b a c k d a tin g to O c to b e r 1921, a n d he o b ta in e d a y e a r’s re m issio n in view o f his R u ssian w ork. T h is m e a n t he co u ld c o m p le te his P h .D . in th e s u m m e r o f 1923. H e w as also a d m itte d as a m e m b e r of T r in ity C ollege a n d soon a fte r his P h .D . h e w as aw a rd ed a C lerk M ax w ell S c h o la rsh ip . H e c o n tin u e d to w rite ecstatically to his m o th e r a b o u t R u th e rfo rd : 18 M a rc h 1923— ‘. . . T h e o n ly th in g th a t eases m y w ork is th e C ro c o d ile ’s care, w h ic h can only be c o m p a re d w ith th e care o f o n e ’s ow n f a th e r .’ 15 J u n e 1923— ‘. . . Y e sterd a y . . . I m et th e C ro c o d ile ju s t as I cam e back fro m b e in g m ad e a D o c to r of P h ilo so p h y . I asked h im : “ D o n ’t y ou th in k , P ro fe sso r R u th e rfo rd , th a t I look w ise r? ” “ W h y s h o u ld y ou look w ise r? ” he rep lied , in trig u e d by m y so m e w h at u n u s u a l q u e stio n . “ I have ju s t b e e n m ad e a d o c to r ” I a n sw ered . H e im m ed ia te ly c o n g ra tu la te d m e a n d said, “ Y es, y o u do look a p p re c i ably w iser an d m o re o v e r y o u ’ve h ad y o u r h a ir c u t ” a n d ro a re d w ith la u g h te r. T a k in g su ch lib e rtie s w ith th e C ro c o d ile is g en erally very risky, since m o st o fte n he sim p ly sen d s y ou to th e devil an d I seem to be th e only one in th e la b o ra to ry w ho d a re s to try . . . . S u ch b e h a v io u r to w a rd s h im fro m a ju n io r is very u n u su a l. S o m e th in g like six tim es I on November 29, 2017 http://rsbm.royalsocietypublishing.org/ Downloaded from
Piotr Leonidovich K a p itza 335
h av e h a d c o m p lim e n ts fro m h im su c h as ‘fo o l’, ‘a s s ’ etc. M o s t o f th e la b o ra to ry is a s to n is h e d h o w su c h jo k e s are p o ssib le . . . .’ A n o th e r e x a m p le of th e k in d o f jo k e K a p itz a h a d in m in d was r e c o u n te d m a n y y e a rs la te r (G 5 5 ). K a p itz a h a d b e e n r a th e r sh o c k ed w h e n at th e s ta r t o f his C a m b rid g e c a re e r, R u th e rf o r d w a rn e d h im th a t he w o u ld n o t to le ra te his m a k in g C o m m u n is t p ro p a g a n d a in th e la b o ra to ry . W h e n a y e a r la te r K a p itz a ’s first m a jo r p a p e r a p p e a re d he trie d a m ild le g -p u ll: ‘I p re s e n te d R u th e rf o r d w ith a r e p r in t a n d I m a d e an in sc rip tio n on it th a t th is w o rk w as p ro o f th a t I h a d com e to his la b o ra to ry to do scien tific w o rk a n d n o t C o m m u n is t p ro p a g a n d a . H e go t e x tre m e ly a n g ry w ith th is in sc rip tio n , sw o re a n d gave m e th e r e p r in t b ack .* I h a d fo re se en th is a n d I h a d a n o th e r r e p r in t in reserv e w ith an e x tre m e ly a p p ro p ria te in sc rip tio n w ith w h ic h I im m e d ia te ly p r e s e n te d h im . . . . R u th e rf o r d h a d a c h a ra c te ris tic a lly h o t te m p e r b u t co o led d o w n ju s t as q u ic k ly ’. T h e p a p e r o n a -tra c k s in s tro n g m a g n e tic fields w as K a p itz a ’s last re se a rc h in R u th e r f o r d ’s p e rso n a l area o f in te re s t. F ro m th e n on he a p p lie d th e im p u lsiv e field te c h n iq u e to o th e r p ro b le m s an d e x te n d e d it to p ro d u c e still h ig h e r fields. T h e first a p p lic a tio n w as a stu d y o f th e Z e e m a n effect in fields u p to 1 3 0 k G f (13, 14) in c o lla b o ra tio n w ith H . W . B. S k in n e r. T h e h o p e w as th a t s o m e th in g new m ig h t tu r n u p at su c h h ig h fields— ty p ic a lly 3 o r 4 tim e s h ig h e r th a n had ever b een u sed b e fo re . H o w e v er, in sp ite o f th e in g e n u ity o f th e te c h n ica l a rra n g e m e n ts (see P I , P 2, P 3), p a rtic u la rly as re g a rd s p ro d u c in g an in te n se lig h t so u rce at ex actly th e rig h t m o m e n t, n o th in g v ery new d id tu r n u p . It w as, of c o u rse , a g re a t feat to m ak e e v e ry th in g w o rk p ro p e rly at th e sam e tim e b u t th e re su lts at th e h ig h fields p ro v e d to be m ain ly no m o re th a n rea so n a b le e x tra p o la tio n s o f w h a t h a d b e e n o b se rv e d b e fo re at low er fields.
A t a b o u t th is tim e K a p itz a s ta rte d an even m o re a m b itio u s p ro je c t for th e p ro d u c tio n o f stro n g im p u lsiv e fields. T h e a c c u m u la to r m e th o d was in p ra c tic e lim ite d to fields o f little m o re th a n lO O kG in a reaso n ab le e x p e rim e n ta l v o lu m e a n d , m o re o v e r, th e a c c u m u la to r re q u ire d difficult re p a irs a fte r c o m p a ra tiv e ly few d isc h a rg es. T h e idea o f a new m e th o d was co n ceiv ed by K a p itz a in 1924 in th e co u rse o f d isc u ssio n s w ith a R u ssian electrical en g in e e r, M . P. K o ste n k o , w h o c a lcu lated th a t it sh o u ld be p ra c tic a b le to d esig n a large d y n a m o th a t on sh o rt c irc u it th ro u g h a su ita b le coil co u ld g e n e ra te v ery h ig h p o w er for a v ery sh o rt tim e an d so p ro d u c e a field o f o rd e r 106 G . T h e sto re d en erg y w o u ld be th e kinetic en e rg y o f ro ta tio n of th e d y n a m o ra th e r th a n th e ch em ical en erg y o f th e a c c u m u la to r. * T h e o rig in a l in s c rib e d r e p r in t is in th e C o c k c ro ft a rc h iv e at C h u rc h ill C o lle g e , C a m b rid g e . t 1G = 1 0 _4T . on November 29, 2017 http://rsbm.royalsocietypublishing.org/ Downloaded from
336 Biographical Memoirs O n c e again K a p itz a w as e n th u sia stic a lly s u p p o rte d by R u th e rfo rd . B ut th e ex p en se in v o lv ed w as o f a b ig g e r o rd e r o f m a g n itu d e th a n co u ld be p ro v id e d fro m C a v e n d ish fu n d s, an d R u th e rfo rd h a d to tu rn to th e D e p a r tm e n t o f S cien tific a n d In d u s tria l R e search ( D .S .I .R .) to realize th is first ste p in to th e ‘m a c h in e a g e ’. A g ra n t o f £ 8 0 0 0 w as m ad e , s p re a d ov er 4 years, an d yet again in e x tre m e ly s h o rt tim e, th e c e n tre piece o f th e sch em e, th e big d y n a m o , h a d b e e n d e sig n e d , b u ilt a n d te s te d at M e tro p o lita n -V ic k e rs in M a n c h e s te r. O n 7 J u ly 1925 K a p itz a w as able to w rite to K o sten k o : ‘. . . T h e m a c h in e has b e e n q u ite a success. . . . I t has b e e n teste d a n d is alre ad y in sta lle d in C a m b rid g e . All th is has tak en a lot o f w ork an d e n erg y , b u t as you see in th e 1 year a n d 4 m o n th s since w e first co n ceiv ed th e idea o f th is m a c h in e it has b een b u ilt a n d in sta lle d . T h a t ’s n o t b a d . . . ’. T h e d y n a m o w as p a te n te d (P4) in th e n a m e s o f K a p itz a a n d K o ste n k o , b u t som e difficult p ro b le m s h a d to be tack led b e fo re it c o u ld be u se d to g e n e ra te large fields. T h e s e to ok y ears to solve, an d a d e ta ile d a c c o u n t of th e w h o le sch em e a p p e a re d in 1927 (16). T h e m o st c h a llen g in g p ro b le m s w ere th e sw itch th a t h a d to close an d o p e n exactly s y n c h ro n o u sly w ith th e d y n a m o cycle, d u rin g w h ich it h a d to c a rry as m u c h as 30 kA an d th e coil th a t had to be m ad e stro n g e n o u g h to w ith s ta n d th e e n o rm o u s m a g n e tic stresses. 1 he d e ta ile d d esig n o f th e coil w as w o rk e d o u t by C o ck cro ft (1928) a n d th e p ro b le m is v ividly illu s tra te d in a le tte r K a p itz a w ro te to R u th e rfo rd on 12 D e c e m b e r 1925 w h en R u th e rfo rd was on his w ay h o m e fro m a trip to th e A n tip o d e s. ‘I am w ritin g to y o u in C airo to tell you th a t w e have alread y o b ta in e d fields o f m o re th a n 270,000 G . . . . W e c o u ld n ’t go f u rth e r b ecause th e coil b u r s t w ith a d e a fe n in g b a n g w h ic h I am su re w o u ld have given you m u c h p lea su re. T h e coil h a d n o t b een e x te rn ally re in fo rc e d and th is we now in te n d to do. . . . I am very h a p p y th a t on th e w hole all w e n t well a n d n ow y ou can be a ssu re d th a t 98% o f th e m o n ey has n o t b een w asted . . . . T h e ac cid e n t w as th e m o st in te re s tin g p a rt o f th e e x p e rim e n t an d finally s tre n g th e n s o u r b elief in success, since we now k n ow exactly w h a t h a p p e n s w hen th e coil b u rsts . W e also now k no w w h a t an arc o f 13,000 A looks lik e .’ A lth o u g h th e h ig h field m ac h in e w o rk ed su ccessfu lly an d en a b le d K a p itz a to o p en u p several new a n d fru itfu l fields of rese a rc h o v er th e n ex t few years, it is p u z z lin g th a t he sh o u ld have c h o sen th e d y n a m o m e th o d ra th e r th a n w h a t w ith h in d sig h t w o u ld seem to have b een sim p le r and c h e ap e r n am ely sto rin g th e en e rg y in a large c ap acito r. In his e arlier p a p e r on th e a c c u m u la to r m e th o d (11) he m e n tio n s th is as a p o ssib ility b u t dism isses it w ith o u t any v ery c o n v in c in g a rg u m e n t. It is tru e th a t large cap acito rs at th a t tim e m ay n o t have b een as reliab le or as ch eap as on November 29, 2017 http://rsbm.royalsocietypublishing.org/ Downloaded from Piotr Leonidovich K a p itza 337
th e y h av e b e c o m e sin ce, b u t a c a p a c ito r o f o rd e r lO m F th a t c o u ld b e c h a rg e d to 2.5 kV w o u ld p ro b a b ly h av e b e e n c h e a p e r a n d s im p le r th a n th e d y n a m o . D is c h a rg e o f s u c h a c a p a c ito r th ro u g h a coil c o m p a ra b le to th a t u se d b y K a p itz a c o u ld h av e p r o d u c e d fields c o m p a ra b le to th o se a c h ie v e d w ith th e d y n a m o . I n d e e d T . F . W all (1924), an e n g in e e r at
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