Piotr Leonidovich Kapitza, 9 July 1894 8 April 1984
Kapitza by B. Kustodiev (portrait owned by the Fitzwilliam Museum and at present on
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Kapitza by B. Kustodiev (portrait owned by the Fitzwilliam Museum and at present on loan to Darwin College, Cambridge). Sheffield U n iv e rs ity , d id p ro p o se th is m e th o d a n d in 1926 d e scrib ed e x p e rim e n ts g iv ing fields as h ig h as 200 k G (b u t fo r r a th e r s h o rte r tim es th a n K a p itz a ’s fields), u sin g a c a p ac ito r o f a b o u t 1 .4 m F ch a rg e d to 2 k V . H o w e v er, W a ll’s coils b u r s t in m o re e x tre m e c o n d itio n s an d he does n o t a p p e a r to h ave o v erco m e th e difficulty n o r c o n tin u e d th e e x p e rim e n ts. A t th e S olvay C o n g re ss in 1930 (28) K a p itz a re fe rre d to W a ll’s lim ite d success as evid en ce for th e u n s u ita b ility o f th e c o n d e n se r m e th o d , b u t th is is h a rd ly c o n v in c in g a n d K a p itz a ’s real reason for n o t try in g th e on November 29, 2017 http://rsbm.royalsocietypublishing.org/ Downloaded from 338 Biographical Memoirs c a p a c ito r m e th o d m ay have b e e n his d islike o f follo w in g a tro d d e n p a th . In fact, w ith th e d e v e lo p m e n t o f m o re reliab le c a p a c ito rs a n d e le c tro n ic m e th o d s o f sw itc h in g a n d re c o rd in g , th e c o n d e n se r m e th o d cam e in to its ow n spo n a fte r th e w a r (fo r a review see C o tti 1960). T h e d y n a m o sy ste m w as re p ro d u c e d a n d su ccessfu lly te s te d in 1939 by Y. T a n a b e at T o h o k u U n iv e rs ity in S e n d a i, b u t it w as d e s tro y e d d u rin g an air raid on 9 J u ly 1945 (see T a n a b e 1949). K a p itz a loved sh o w in g off th e special fe a tu re s o f his in sta lla tio n . E v e n th o u g h th e m a c h in e ry w as e la b o ra te ly m o u n te d to avoid tra n s m ittin g v ib ra tio n s , th e c o n sid e ra b le m e c h a n ic a l shock a sso ciated w ith a loss of 2 0 % o f th e k in etic e n e rg y o f th e d y n a m o m ig h t easily h ave u p s e t th e d elicate re c o rd in g in s tru m e n ts . T o av oid an y d is tu rb a n c e , th e coil a n d th e re c o rd in g in s tr u m e n ts w ere p laced a b o u t 20 m e tre s aw ay fro m th e m ac h in e so th a t th e seism ic w ave th ro u g h th e g ro u n d a rriv e d on ly a fte r th e e x p e rim e n t w as o v er, a n d th e n e c essa ry space w as p ro v id e d b y an o u tb u ild in g o f th e C h e m is try D e p a r tm e n t. L a te r, w h e n th e w o rk w as tra n s fe rre d to th e R oyal S o ciety M o n d L a b o ra to ry , th e long ‘m a g n e t h a ll’ b ecam e th e c e n tra l fe a tu re o f th e b u ild in g , w ith rese a rc h ro o m s on e ith e r side o f it. T h is tu rn e d o u t to be a very successfu l d esig n even a fte r th e h ig h field m a c h in e ry h a d go ne, b ecau se th e long hall p ro v id e d c o n v e n ie n t o p p o rtu n itie s for rese a rc h e rs to m ee t a n d e x ch an g e ideas. T o b rin g h o m e th e n o v e lty o f an e x p e rim e n t lastin g su c h a s h o rt tim e K a p itz a w as fo n d o f te llin g tw o little jo k es. O n e w as th a t j ^ q S was a very long tim e if you k n ow w h a t to do w ith it, a n d th e o th e r w as th a t he m u st c e rta in ly be th e h ig h e s t p a id s c ie n tist in th e w o rld since he receiv ed a full acad em ic salary for w o rk lastin g in to ta l only a few seco n d s in a year. O n one occasio n — a ra re o n e — K a p itz a w as u p sta g e d in sh o w in g off his h ig h field e q u ip m e n t. T h e o ccasion w as a v isit fro m R. W . W o o d , th e A m e ric a n p h y sic ist, h im s e lf fam o u s for his in g e n u ity a n d his sc ep ticism o f w h a t o th e rs co u ld show h im . K a p itz a p re p a re d a s trik in g d e m o n stra tio n o f th e g rea t s tre n g th o f his fields by sh o o tin g a glass ro d im m e rse d in liq u id o x yg en (stro n g ly p a ra m a g n e tic ) u p to th e ceiling, w h e re it s h a tte re d , w h e n th e im p u lsiv e field w as a p p lie d . W o o d w as a c co m p a n ie d by R u th e rfo rd a n d o th e r C a v e n d ish figures a n d th e y looked e x p e c ta n tly to see w h a t im p re ssio n h a d b e e n m ad e on h im . H e , h o w ever, d id n o t seem p a rtic u la rly im p re sse d . In ste a d , he w alked up to th e coil, took o u t th e sm all vessel o f liq u id oxygen a n d calm ly d ra n k K a p itz a ’s health! T h e sp e c ta to rs, n o t fam iliar w ith th is r a th e r difficult trick , w h ich d e p e n d s on k e e p in g th e liq u id in th e sp h e ro id a l state, w ere r a th e r reliev ed to see W o o d sp it o u t th e liq u id again a fte r a few secon ds. K a p itz a ’s first m a jo r rese a rc h w ith th e n ew e q u ip m e n t w as an ex ten siv e stu d y o f how th e electrical resista n c e o f m etals increases w ith m ag n e tic field (17—21). T h is w as c h o sen p a rtly becau se it w as th e sim p lest k in d o f m e a s u re m e n t to m ake in a p u lse d field a n d p a rtly becau se it h ad b een relatively little e x p lo re d b efo re. A g en eral fea tu re o f th e re su lts w as th a t on November 29, 2017 http://rsbm.royalsocietypublishing.org/ Downloaded from Piotr Leonidovich K a p itza 339
th e re s is ta n c e , a fte r s ta r tin g o ff q u a d ra tic a lly in field, e v e n tu a lly c h a n g e d a s y m p to tic a lly to a lin e a r v a ria tio n , o fte n k n o w n as K a p itz a ’s law o f m a g n e to re s is ta n c e . H e w as a b le to fit h is re s u lts to a th e o r y b a s e d e s s e n tia lly o n th e ad hoc a s s u m p tio n th a t id ea lly th e b a sic law w as lin e a r b u t th a t th is id ea l b e h a v io u r w as d is tu r b e d b y th e p re s e n c e o f ra n d o m ly d ire c te d in te r n a l m a g n e tic fields s u p e rim p o s e d o n th e a p p lie d field. A lth o u g h th is b o ld a tte m p t to give a p h e n o m e n o lo g ic a l th e o r y o f m a g n e to re s is ta n c e a t a tim e w h e n th e e le c tro n ic th e o r y o f m e ta ls w as still in its in fa n c y w as u s e fu l in p r o v id in g a g u id e to f u r th e r e x p e rim e n ts , it h a s n o t s to o d th e te s t o f tim e . L a te r e x p e rim e n ts , p a rtic u la rly a t lo w e r te m p e r a tu r e s a n d w ith sin g le c ry s ta ls , c o u p le d w ith a b e tte r u n d e r s ta n d in g o f th e th e o r y , s h o w e d th a t K a p itz a ’s lin e a r law w as n o t re a lly b asic b u t a c o n s e q u e n c e p a rtly o f th e re la tiv e ly h ig h te m p e r a tu r e o f h is m e a s u r e m e n ts (o n ly d o w n to liq u id n itr o g e n te m p e ra tu re ) a n d p a rtly o f h is u se o f p o ly c ry s ta llin e sa m p le s in m o st o f h is e x p e rim e n ts (fo r a re c e n t d is c u s s io n see P ip p a r d 1979). K a p itz a h im s e lf re a liz e d th a t e x p e rim e n ts a t lo w e r te m p e r a tu r e s w o u ld p r o b a b ly b e e s se n tia l fo r a b e tte r u n d e r s ta n d in g o f m e ta ls a n d th is w as o n e o f th e m a in m o tiv a tio n s fo r h is w o rk o n h y d r o g e n a n d h e liu m liq u e fa c tio n so o n a fte r. T w o m o re re s e a rc h e s at h ig h field s, b o th a g a in o f a n e x p lo ra to ry n a tu r e , w e re th e n c a rrie d o u t. T h e s e w e re s tu d ie s o f th e m a g n e tiz a tio n o f a v a rie ty o f s u b s ta n c e s (30) a n d o f m a g n e to s tric tio n , m a in ly o f sin g le c ry s ta l b is m u th (33—35). A t th e h e a rt o f b o th s tu d ie s w as an in g e n io u s in s tr u m e n t (29) th a t c o u ld b e u s e d e ith e r as a b a la n c e to m e a s u re th e fo rc e o n a s a m p le in a n in h o m o g e n e o u s m a g n e tic field, a n d h e n c e th e m a g n e tiz a tio n , o r as a n e x te n s o m e te r to m e a s u re th e c h a n g e o f le n g th o f a ro d fixed a t its o th e r e n d . T h e id ea w as to a p p ly th e fo rce o r th e c h a n g e o f le n g th to a d ia p h r a g m se alin g th e b o tto m o f a sm all v essel c o n ta in in g oil a n d its e lf c o m p le te ly im m e rs e d in a b a th o f th e sam e oil. D is p la c e m e n t o f th e d ia p h r a g m s q u ir te d oil th r o u g h a sm all h o le b e tw e e n th e in n e r vessel a n d th e o u te r b a th a n d so tilte d a lig h t m ir r o r m o u n te d o n a p iv o t n e a r th e h o le. B y su ita b le d e s ig n th e d e fle c tio n o f a lig h t b e a m reflec ted b y th e m ir r o r c o u ld b e m a d e p r o p o rtio n a l to th e fo rc e o r to th e e x te n sio n . T h e m a g n e tiz a tio n m e a s u re m e n ts d id n o t rev eal a n y th in g v e ry n o v el, fo r it tu r n e d o u t o n ce a g a in th a t th e law s e s ta b lis h e d a t lo w e r fields c o u ld safely b e e x tra p o la te d in to th e n e w ra n g e o f h ig h e r fields. T h e o b s e rv a tio n o f m a g n e to s tric tio n in b is m u th w as, h o w e v e r, th e first su c h o b s e rv a tio n o n a d ia m a g n e tic a n d K a p itz a also d e v e lo p e d th e th e o ry fo r s p e c ify in g h o w th e a n is o tro p y o f th e effect w as d e te r m in e d b y c ry sta l s y m m e try . K a p itz a ’s in te r e s t in th e s o m e w h a t a n o m a lo u s p ro p e rtie s o f b is m u th s ta r te d a tra d itio n th a t c o n tin u e d lo n g a fte r h e h a d left C a m b rid g e (see S h o e n b e rg 1978), a n d h is e m p h a s is o n th e im p o rta n c e o f c h e m ic a l p u r ity a n d sin g le c ry sta ls w as also a v a lu a b le legacy to th o se w h o fo llo w ed in h is fo o tste p s. I n th e c o u rse o f all th is w o rk , th e r e w e re sev eral im p o r ta n t on November 29, 2017 http://rsbm.royalsocietypublishing.org/ Downloaded from
340 Biographical Memoirs d e v e lo p m e n ts in K a p itz a ’s life a n d care e r. In J a n u a ry 1925 he was a p p o in te d to an official U n iv e rs ity p o sitio n , th a t o f A s sista n t D ire c to r of M a g n e tic R e se a rc h . In O c to b e r 1925 he w as ele c te d to a R e se a rc h F e llo w sh ip at T r in ity C ollege a n d he b e c am e a p o p u la r m e m b e r of th e H ig h T a b le , m ix in g easily w ith y o u n g a n d old of all sp ecialties. H e g rea tly v a lu e d his asso ciatio n w ith th e C ollege w h e re he lived u n til h e w as m a rrie d a n d w h e re he c o n tin u e d to d in e fre q u e n tly d u r in g th e rest of his tim e in C a m b rid g e . H e w as p a rtic u la rly p leased w h e n , m a n y y ears late r (in 1966), he w as ele c te d to an H o n o ra ry F e llo w sh ip . In th e s p rin g o f 1927 he w e n t to P a ris a n d on 27 A p ril w ro te to R u th e rfo rd (his sp e llin g has n o t b e e n c o rre c te d ): ‘I am g o ing to be m a rrie d . . . . W h a t do y o u th in k a b o u t it??!! I feer you are r a th e r an g rey . T h is is w h y I p ro p o se to have no h o n e y m o o n an d b rin g m y wife in a few d a y ’s tim e a fte r m y w e d d in g to C a m b rid g e . . . I h o p e you u n d e rs ta n d th a t I am a v ictim e o f m y ow n 300,000 gau sse a n d I have to confece th a t th e dose w h ic h I receiv ed is r a th e r a stro n g one. . . . Y o u see th a t even in m o re im p o rta n t q u e stio n s I have a q u ick d essisio n a n d g rea d sp eed o f a c tio n .’ T h e lady in q u e s tio n w as A n n a A lekseyevna, d a u g h te r o f th e A d m ira l K ry lo v m e n tio n e d earlier. A lth o u g h A n n a ’s fa th e r stay ed in R u ssia a fte r th e R ev o lu tio n h e r m o th e r e m ig ra te d to P a ris a n d it w as th e re th a t A n n a c o m p le te d h e r e d u c a tio n as an arch aeo lo g ist; she w as also an a c c o m p lish e d a rtist. R u th e r f o r d ’s rep ly (2 9 th A p ril) to K a p itz a ’s a n n o u n c e m e n t also d e serves q u o ta tio n : ‘I receiv ed y o u r le tte r at b rea k fa st th is m o rn in g a n d I rea d it w ith m u c h in te re st an d a m u se m e n t. . . . M y w ife a n d I u n ite in se n d in g o u r w a rm e st c o n g ra tu la tio n s. . . . T h e y say it is a b a d w ife th a t does n o t h elp a little, so I shall ex p ect y o u r w ork to m ake even faster p ro g re ss. . . . I am n o t s u rp rise d at th e new s as I h a d h e a rd ru m o u rs of y o u r m ag n e tic s u sc e p tib ility u n d e r in te n se a ttra c tiv e fie ld s.’ T h e m arria g e w as a very h a p p y one an d A n n a w as n o t only a c h a rm in g h o stess to th e ir m an y frie n d s, b u t a g reat s u p p o rt to P e te r in th e difficult tim es he h ad to go th ro u g h on several occasions later. T w o sons w ere b o rn in C a m b rid g e : S erg ei in 1928, a d istin g u is h e d p h y sic ist an d a v ery , successful p re s e n te r o f p o p u la r science o n S oviet television , an d A n d re i in 1931, a well k n o w n A n ta rc tic e x p lo re r an d g e o g ra p h e r. In 1929 K a p itz a w as e lected to F e llo w sh ip o f the R oyal Society at th e first electio n a fte r he h a d b een p ro p o se d . T h is in itself w as a rare d istin c tio n b u t even ra re r was th e electio n of a fo re ig n e r— fo r K a p itz a h ad alw ays reta in e d his S o viet c itiz e n sh ip . In fact th e S ta tu te s at th a t tim e d id n o t ex clu de th e electio n of a fo re ig n e r p ro v id e d th a t he w as an ‘in h a b ita n t of H is M a je s ty ’s d o m in io n s ’, b u t su ch electio n s w ere in d eed rare, th e on November 29, 2017 http://rsbm.royalsocietypublishing.org/ Downloaded from
Piotr Leonidovich K a p itza 341
p re v io u s o ne h a v in g b e e n in 1914! B u t to cap e v e ry th in g , his scientific d is tin c tio n w as a lm o st sim u lta n e o u sly rec o g n ize d in his ow n c o u n try by e le c tio n to C o rre s p o n d in g M e m b e rs h ip o f th e S o v iet A c a d e m y of S cien ces. E a rly in 1930 K a p itz a d isc u sse d w ith R u th e rfo rd th e p o ssib ility of s e ttin g u p a n ew la b o ra to ry th a t c o u ld h o u se n o t o n ly th e h ig h field e q u ip m e n t, b u t also p ro v id e c ry o g e n ic facilities to e x te n d his rese a rc h e s to m u c h lo w er te m p e ra tu re s . R u th e rf o r d b a c k ed th is idea e n th u sia stic a lly a n d p e rs u a d e d th e R oyal S o ciety to give £ 1 5 000 fo r b u ild in g su ch a la b o ra to ry . T h e m o n e y w as fo u n d fro m a b e q u e s t to th e R oyal S o ciety by L u d w ig M o n d a n d th e n ew la b o ra to ry w as called th e R oyal S ociety M o n d L a b o ra to ry . A t th e sam e tim e K a p itz a w as a p p o in te d to a R oyal S o ciety M essel P ro fe s s o rs h ip . A ll th e c o m p lic a te d n e g o tia tio n s b e tw e e n th e R o yal S o ciety , th e U n iv e rs ity a n d D .S .I .R . w ere c o m p le te d re m a rk ably q u ic k ly a n d sm o o th ly — p a rtly b e c au se o f th e d o m in a n t p o sitio n of R u th e rf o r d in all th re e b o d ies a n d p a rtly th ro u g h th e d riv e o f K a p itz a a n d C o c k c ro ft— a n d b y 1931 a h a n d s o m e m o d e rn b u ild in g d e sig n e d by th e a rc h ite c t H . C. H u g h e s w as g o ing u p in th e c o u rty a rd o f th e C a v e n d ish . T h e first ste p in th e a d v an ce to w a rd s lo w er te m p e ra tu re s w as a h y d ro g e n liq u e fie r th a t w as c o m p le te d b y K a p itz a in c o lla b o ra tio n w ith C o c k c ro ft sh o rtly b e fo re th e M o n d L a b o ra to ry w as read y (36). A difficulty in th e liq u e fa c tio n o f h y d ro g e n is th a t e x tre m e ly p u re h y d ro g e n m u st be u se d to avoid c o n d e n se d im p u ritie s b lo ck in g u p th e n a rro w -b o re re g e n e ra to r tu b e s . T h is difficulty w as in g en io u sly c irc u m v e n te d by u sin g only a sm all v o lu m e o f e x tre m e ly p u re h y d ro g e n in a closed c irc u it, w h ich cooled o rd in a ry c o m m e rc ial h y d ro g e n a n d allow ed th e im p u ritie s to se ttle at th e b o tto m o f th e h e a t e x c h an g e r w ith o u t any b lockage. A special fe a tu re of th e liq u efier ro o m w as a v ery lig h t ro o f d e sig n e d to blo w off a n d relieve th e p re s s u re in th e ev e n t o f an ex p lo sio n. K a p itz a w as fo n d of w a rn in g n e rv o u s v isito rs o f th is p o ssib ility , th o u g h in th e ev en t it n e v e r o c c u rre d . In c o n s tru c tin g a h e liu m liq u efier, K a p itz a as u sual chose a co m p letely o rig in al m e th o d (39, 40, P 10). In ste a d o f rely in g on coolin g w ith liq u id h y d ro g e n to get th e h e liu m belo w its J o u le - T h o m s o n in v ersio n te m p e ra tu re , th e m ain co o ling w as achiev ed by ad ia b a tic e x p a n sio n in a p isto n an d c y lin d e r en g in e. T h is of co u rse w as a well k n o w n p rin c ip le b u t u p to th e n th e p ro b le m o f how to lu b ric a te th e p isto n h ad n e v e r been solved. K a p itz a ach iev ed th is by th e in g en io u s e x p e d ie n t o f u sin g th e h e liu m gas itself as th e lu b ric a n t. T h e m ac h in e was c o m p le te d in 1934 and p ro v ed im p o rta n t n o t only in p ro v id in g liq u id h e liu m for over 10 years of C a m b rid g e rese a rc h , b u t in s u p p ly in g th e basic idea for a facto ry b u ilt h e liu m liq uefier d esig n e d by S. C. C o llin s (1947) at the M a ssa c h u setts In s titu te o f T e c h n o lo g y ( M .I .T .) . T h e co m m ercial availab ility o f these C o llins m ac h in es rev o lu tio n ize d low te m p e ra tu re physics by m ak in g on November 29, 2017 http://rsbm.royalsocietypublishing.org/ Downloaded from 342 Biographical Memoirs liq u id h e liu m easily accessib le all o v e r th e w o rld , r a th e r th a n at o n ly a few sp ecialized c e n tre s. K a p itz a h a d h o p e d th a t C a m b rid g e w o u ld h av e th e first liq u id h e liu m in E n g la n d , b u t he w as u p s ta g e d by F . A. L in d e m a n n at O x fo rd , w h o b ro u g h t M e n d e ls s o h n o v e r fro m G e rm a n y w ith one o f S im o n ’s m in ia tu re liq u efiers a n d tr iu m p h a n tly a n n o u n c e d (L in d e m a n n & K eeley 1933) th e first liq u id h e liu m in E n g la n d a y e a r ah e ad o f K a p itz a . H o w e v er, K a p itz a c o u ld claim th a t his w as th e first liq u id h e liu m th a t c o u ld be loo k ed at (th e O x fo rd liq u id w as h id d e n in a m eta l vessel). T h e
first liquid helium in the Royal Society Mond Laboratory, 21 April 1934. T h e o p e n in g o f th e M o n d L a b o ra to ry by S ta n le y B ald w in , th e n C h a n c e llo r o f th e U n iv e rs ity , w as a g rea t occasio n w ith a lu n c h e o n at C o rp u s C h risti C ollege h o ste d b y th e V ic e -C h a n c e llo r, follo w ed by sp eech es in th e A rts S ch o o l, a n d finally th e o p e n in g its e lf w ith a g ild e d c ro c o d ile -sh a p e d key a n d a v isita tio n o f th e la b o ra to ry . B a ld w in ’s speech a c ce p tin g th e R oyal S o c ie ty ’s g ift to th e U n iv e rs ity cau se d som e a m u se d p u z z le m e n t, fo r m u c h o f it w as a lm o st id en tic a l w ith w h a t R u th e rfo rd h a d said e a rlie r in th e p ro c e e d in g s. I t seem s th a t R u th e rfo rd h a d fo rg o tte n he h a d alre ad y u se d his re m a rk s in b rie fin g B aldw in! D u rin g th e la b o ra to ry v isit K a p itz a p ro v id e d a nice ex am p le o f his style of irre v e re n t teasin g . H e w as o v e rh e a rd rep ly in g to a q u e ry fro m B aldw in: ‘Y es in d ee d . Y o u can believe m e, I ’m n o t a p o litic ia n ’. In th e co u rse of th e o p e n in g , a lifesize c a rv in g o f a cro co d ile on th e w all ju s t o u tsid e th e m ain e n tra n c e an d a b a s -re lie f o f R u th e rfo rd h im self, in sid e th e foyer, b o th by E ric G ill, w ere rev ealed for th e first tim e; th e b a s -re lie f gave rise to som e c o n tro v e rsy a b o u t th e sh ap e of R u th e r f o r d ’s nose (see O lip h a n t 1972).
S o m e th in g sh o u ld now be said a b o u t o th e r asp ects o f his w ork an d leisu re in C a m b rid g e . T h e K a p itz a C lu b (see p. 346) re p re s e n ts his m ajo r c o n trib u tio n , alb eit in fo rm a l, to te a c h in g activ ities. H is o th e r tea c h in g on November 29, 2017 http://rsbm.royalsocietypublishing.org/ Downloaded from Piotr Leonidovich K a p itza 343
to o k th e fo rm o f s u p e rv is in g re s e a rc h s tu d e n ts a n d so m e le c tu rin g . T h e la tte r c o n s is te d o f e ig h t w eek ly le c tu re s o n ‘R e c e n t re se a rc h e s in m a g n e t is m ’ a n d I h av e lively m e m o rie s o f a tte n d in g th is c o u rse in 1932. I fo u n d it fa s c in a tin g n o t o n ly fo r its c o n te n t, b u t also fo r th e in trig u in g p re s e n ta tio n . H is s tro n g R u ssia n a c ce n t a n d r a th e r h ig h -p itc h e d voice, h is p e c u lia r E n g lis h c o n s tru c tio n s a n d his h a b it o f w ritin g on th e b la c k b o a rd s o m e th in g q u ite d iffe re n t fro m w h a t he h a d said, w ere e n te rta in in g , b u t s o m e tim e s m a d e it difficult to follow . O n c e I cam e u p a fte r th e le c tu re a n d asked h im to clarify a c o n tra d ic tio n in m y n o tes. H is rep ly w as ‘I f I m ake e v e ry th in g so c le a r th a t th e re are no c o n tra d ic tio n s , th e re is n o th in g left fo r y o u to th in k a b o u t.’ H e also gave m an y sem i- p o p u la r le c tu re s a n d o n ce d e s c rib e d h is te c h n iq u e : ‘I try to p itc h it so th a t 9 5 % u n d e rs ta n d 5 % a n d th a t 5% fu lly u n d e rs ta n d 9 5 % . I alw ays tell a jo k e in th e first 5 m in u te s a n d if th e y lau g h I k n o w th e y are u n d e rs ta n d in g m y E n g lis h w ell e n o u g h .’ K a p itz a s u p e rv is e d o nly a few re se a rc h s tu d e n ts . T h e e a rlie st w ere J. D . C o c k c ro ft, s u b s e q u e n tly fam o u s fo r his n u c le a r p h y sic s w ork, a n d W . L . W e b s te r, w h o d id som e p io n e e r w o rk on fe rro m a g n e tis m . T h e o n ly o th e rs b e fo re th e m ove to th e M o n d w ere D . S. K o th a ri, w h o late r m ad e d is tin g u is h e d c o n trib u tio n s to a stro p h y sic s in In d ia , a n d A. G . H ill w h o jo in e d K o th a ri b riefly. A t th a t tim e th e u su al p ra c tic e in th e C a v e n d ish w as fo r th e C a v e n d ish P ro fe sso r to be th e official su p e rv is o r of all th e re se a rc h s tu d e n ts , th o u g h th e d e ta ile d su p e rv isio n w as o fte n d o n e by R u th e r f o r d ’s lie u te n a n ts. H o w e v er, a fte r th e m ove to th e M o n d , K a p itz a w as n a m e d as th e official su p e rv is o r o f tw o m o re rese a rc h s tu d e n ts : m y self, in 1932, a n d C. J. M iln e r, la te r P ro fe sso r o f A p p lie d P h y sics at th e U n iv e rs ity o f N ew S o u th W ales, in 1933. B o th M iln e r a n d I recall K a p itz a ’s s tim u la tin g su p e rv isio n a n d his o rig in a l w ay o f h e lp in g to o v e rc o m e o u r e x p e rim e n ta l difficulties. I was p u t on to th e m e a s u re m e n t o f th e tra n s v e rs e m a g n e to s tric tio n o f b is m u th c ry sta ls in th e field o f an o rd in a ry e le c tro m a g n e t. T h e e x p e cte d ch an g e of le n g th w as v ery sm all, o n ly o f o rd e r 1 0 ~ 7 cm , an d w h e n I w as feeling a b it d e s p e ra te b ec au se th e a p p a ra tu s w as still 100 tim es too in sen sitiv e, K a p itz a w o u ld p o in t o u t h a lf a d o zen sim p le im p ro v e m e n ts, each of w h ich s h o u ld give a fa c to r 2 im p ro v e m e n t a n d th e n th ro w in p e rh a p s tw o r a th e r u n o rth o d o x su g g e stio n s, each of w h ich s h o u ld give a fac to r 3. So th e p ro b le m seem ed to be solved, w ith even a b it in h a n d , since 2 6 x 3 2 is n e a rly 600. B u t w h e n he h ad g one an d I s ta rte d try in g his ideas, th e fac to rs o f 2 p ro v e d to be o n ly p e rh a p s 1.2 a n d th e facto rs o f 3 p e rh a p s 1.5 so th a t th e gain w as only p e rh a p s 6 r a th e r th a n 600. H o w ev er, I w as th a t m u c h n e a re r m y goal a n d read y for th e n e x t b a tc h of su g g estio n s. M iln e r w as also im p re sse d by th e fe rtility o f K a p itz a ’s in v en tiv e n e ss, th o u g h he g rad u a lly le a rn t th a t m an y of K a p itz a ’s in g en io u s su g g estio n s c a rrie d som e fatal flaw. B u t even if on ly p e rh a p s one in five p ro v ed so u n d , this one m ig h t well h it th e ja c k p o t an d o verco m e th e difficulty. on November 29, 2017 http://rsbm.royalsocietypublishing.org/ Downloaded from 344 Biographical Memoirs K a p itz a h a d m an y in te re s ts an d skills o u tsid e his scientific w ork. O n e o f his early e n th u s ia sm s w as th e in te rn a l c o m b u s tio n en g in e. S oo n a fte r his a rriv al in C a m b rid g e he b o u g h t a m o to r-c y c le a n d on 16 A u g u s t 1921 he w ro te to his m o th e r: ‘E v e ry th in g w e n t v ery well a lth o u g h we w e r e n ’t g o in g slow ly, b u t th e n we h a d a spill. T h e r e are six b ru ise s an d sc ra tch e s o n m y b o d y b u t th e w o rst is m y face. If y ou co u ld only see it! . . . W h e n I cam e in to th e lab. I c re a te d q u ite a se n sa tio n . N o w I shall be m u c h m o re c a re fu l.’ B efore long he g ra d u a te d to a car (first a L a g o n d a , th e n a T r iu m p h an d later a V au x h all, c h o sen b ecau se full w o rk in g d ra w in g s w ere available) an d a c q u ire d a re p u ta tio n for r a th e r reckless d riv in g . W h e n he w as go in g p a rtic u la rly fast he w o u ld re a ssu re a n e rv o u s p a sse n g e r b y sayin g th a t his h ig h s p e e d o m e te r re a d in g was in k .p .h . r a th e r th a n m .p .h . O n one occasion he solved th e p ro b le m o f o v e rta k in g a slow car o b se rv in g th e sp eed lim it in R ic h m o n d P a rk by g o in g off th e ro ad on to th e g rass an d p assin g rap id ly on th e w ro n g side. P e rh a p s th e b e st sto ry is of his T r in ity frie n d , th e R e v e ren d F. A. S im p so n , s ittin g b e h in d h im on a c o u n try driv e. As th e y a p p ro a c h e d a d a n g e ro u s c o rn e r K a p itz a p re sse d th e a c ce lera to r an d tu rn e d ro u n d to say ‘P ra y G o d S im p so n , p ra y G o d ’. It seem s th e p ra y e rs w ere effective. H e h ad, in d ee d , r a th e r a w eakn ess fo r teasin g clerg y m en ; a n o th e r ex am p le w as w h e n a c le rg y m a n , a g u est d in in g in H all, asked K a p itz a w ho E d d in g to n w as an d w as to ld ‘H e know s far m o re a b o u t th e H e a v e n s th a n yo u d o ’. As alread y m e n tio n e d , he w as skilled at c o n s tru c tin g a n d h a n d lin g d elicate e q u ip m e n t a n d he loved any activ ity in v o lv in g fine m ec h a n ism s. O ne of his h o b b ies, d a tin g fro m his schooldays, w as re p a irin g w atch es and clocks an d m ak in g th e re p la c e m e n t p a rts him self. A n o th e r h o b b y in v o lv in g m an u a l skill w as c o n ju rin g . S ergei K a p itz a recalls how fasci n a te d he w as as a sm all boy seeing his fa th e r a p p e a r to sw allow tab le knives an d b ite b its off ch in a p lates. E. T . S. W a lto n re m e m b e rs a tra in jo u rn e y w h en K a p itz a sh o w ed off th e th re e -c a rd tric k ( ‘find th e la d y ’) as co n v in cin g ly as any p ro fessio n al tric k ste r. In his m em o irs (1968) th e fam ou s, b u t ra th e r staid , a p p lie d m a th e m a tic ia n T im o s h e n k o recalls K a p itz a ’s glee in m ak in g v a rio u s e m in e n t sc ie n tists look a little silly by in v olv in g th e m as stooges in his d e m o n s tra tio n s . A ra th e r d iffe re n t ty p e of skill at w h ich K a p itz a excelled w as chess an d S m y slo v , th e R u ssian o n e -tim e w o rld c h a m p io n , said th a t he co u ld n o t take a gam e w ith K a p itz a lightly. F inally, som e c o m m e n ts on K a p itz a ’s p e rso n a lity an d style as re m e m b e re d by th o se w ho knew h im in his C a m b rid g e days. A t tim es he cou ld be alm o st a te x t-b o o k ex am ple o f the a b s e n t-m in d e d p ro fe sso r. I f a q u e stio n w as a d d re sse d to h im at su ch a tim e his typ ical reactio n w ould be ‘W h a t you say?’ an d only a fter several re p e titio n s o f th e q u e stio n and on November 29, 2017 http://rsbm.royalsocietypublishing.org/ Downloaded from Piotr Leonidovich 345
h is ‘W h a t y o u sa y ? ’ w o u ld h e d e a l w ith th e q u e s tio n — th o u g h s o m e tim e s h e m ig h t s im p ly w a lk off le a v in g th e q u e s tio n u n a n s w e re d . O c c a sio n a lly th is m a y h a v e b e e n a p lo y to g ive h im s e lf tim e to th in k , b u t u s u a lly it w as g e n u in e a b s e n t- m in d e d n e s s , o r r a th e r a n in d ic a tio n th a t h is m in d w as fu lly o c c u p ie d b y s o m e th in g else. I n d e e d w h e n h e w as try in g o u t a n e w id e a in th e la b o r a to r y h e w o u ld b e c o m e so c o m p le te ly a b s o rb e d as to lose all se n se o f tim e a n d s o m e tim e s A n n a w o u ld h a v e to c o m e in to re m in d h im th a t th e y w e re e x p e c tin g g u e s ts to d in n e r . H e p a id little a tte n tio n to h is p e rs o n a l a p p e a ra n c e a n d a C a m b rid g e le g e n d is th a t h e w as on ce re fu s e d a d m is s io n to a fo rm a l g a th e r in g a t th e S e n a te H o u s e b e c a u se he w as w e a rin g a b la z e r a n d c a rp e t s lip p e rs r a th e r th a n th e o b lig a to ry d a rk s u it a n d b la c k sh o e s. B u t m o re o fte n h e w as c h e e rfu l a n d o u tg o in g , a g re a t c h a rm e r a n d v e ry g o o d c o m p a n y . H e lo v ed an a rg u m e n t, he fo u n d s o m e th in g in te r e s tin g to say o n a lm o s t a n y s u b je c t a n d h e w as an e x c e lle n t r a c o n te u r w ith an e n o rm o u s re p e r to ire o f a n e c d o te s, o fte n o f th e sh a g g y d o g v a rie ty , b u t u s u a lly w ith a R u s s ia n tw ist. O c c a sio n a lly th e p o in t o f th e s to ry w o u ld b e o b s c u re to so m e o n e n o t fa m ilia r w ith R u s s ia n tr a d itio n s o r b e c a u s e o f K a p itz a ’s p e c u lia r E n g lis h , b u t h is la u g h te r o v e r h is o w n jo k e w as so in fe c tio u s th a t th o se a ro u n d h im fo u n d th e m se lv e s jo in in g in , e v e n if th e y h a d n ’t a lto g e th e r u n d e rs to o d th e jo k e . I t w as p e rh a p s th e c o m b in a tio n o f h is o u tg o in g p e rs o n a lity , h is g e n u in e in te r e s t in p e o p le a n d his c u rio s ity a b o u t w h a t m a d e th e m tick th a t e n a b le d h im to o v e rc o m e sh y n e ss a n d re se rv e a n d m ak e frie n d s o f p e o p le like th e r a th e r re s e rv e d C h a d w ic k , th e ta c itu r n C o c k c ro ft, th e u s u a lly sile n t D ira c a n d e v en th e a u s te re A . E. H o u s m a n o f T r in ity . T h e s e q u a litie s also e n a b le d h im to g a in th e f rie n d s h ip a n d s u p p o rt o f R u th e rf o r d , th o u g h h e re , as d isc u s s e d b y W ilso n (1983), o th e r fa c to rs w e re also re le v a n t. R u th e r f o r d seem s to h av e b e e n c a p tiv a te d b y K a p itz a ’s b o ld n e s s , b o th his b o ld n e s s o f scien tific v isio n a n d his b o ld n e ss in tr e a tin g R u th e r f o r d w ith m u c h less re v e re n c e a n d re s p e c t th a n th e g re a t m a n w as a c c u s to m e d to fro m h is ju n io r s , w h ilst a t th e sam e tim e o p e n ly sh o w in g his a d m ira tio n o f R u th e rf o r d ’s g en iu s. A su b je c t o f jo k in g in th e C a v e n d ish w as R u th e r f o r d ’s fo n d n e s s fo r u s in g b lu n t s tu b e n d s o f p e n c il, a n d o n R u th e r f o r d ’s 6 0 th b irth d a y K a p itz a p re s e n te d h im w ith a silv e r p ro p e llin g p e n c il a c c o m p a n ie d b y a fa c e tio u s c o n g ra tu la to ry le tte r. R u th e rf o r d seem s to h av e e n jo y e d th is k in d o f lig h th e a rte d tea sin g , th o u g h K a p itz a ’s g ift d id n o t w e a n h im fro m h is s tu b e n d s. W h e n K a p itz a h a d s e ttle d in M o sco w so m e y e a rs la te r, R u th e rf o r d w ro te h ow m u c h h e m isse d th e ir e v e n in g w alks a fte r S u n d a y d in n e r in T r in ity . T w o o th e r a sp ec ts o f K a p itz a ’s p e rs o n a lity w ill b e e v id e n t fro m m u c h o f w h a t h as b e e n said: h is fo n d n e ss o f b o a s tin g a n d e x a g g e ra tio n a n d h is e n o rm o u s se lf-c o n fid e n c e . H o w e v e r, u su a lly th ese w e re d isp la y e d in a so m e w h a t to n g u e -in -c h e e k m a n n e r w h ic h e n d e a re d r a th e r th a n rep e lle d . F o r in sta n c e N . K u r ti, recalls th a t w h e n K a p itz a v isite d B e rlin in 1930 a n d F . E . S im o n (w ho lik ed p re c isio n ) asked fo r his ex act E n g lish on November 29, 2017 http://rsbm.royalsocietypublishing.org/ Downloaded from 346 Biographical Memoirs a d d re ss, he said w ith a c h u c k le ‘K a p itz a , E n g la n d ’ w ill do. H e loved ab o v e all to achieve s o m e th in g th a t w as u n iq u e o r at least e x c e p tio n a l. T h u s he w as p r o u d o f his u n iq u e d is tin c tio n o f b e in g b o th an F .R .S . a n d a S o v iet A c a d e m ic ia n a n d o f his e x tre m e ly rare s ta tu s o f re m a in in g a S o v iet c itiz e n y et h o ld in g an im p o r ta n t p o st in E n g la n d . H is self- co n fid e n ce w as b ased on rea listic a sse ssm e n t o f th e p ro b le m in h a n d , an d u su a lly th is self-c o n fid e n c e p ro v e d ju stifie d by th e successfu l o u tc o m e of w h a te v e r he w as try in g to ach iev e. R u th e rf o r d w as c e rta in ly im p re ss e d to see th a t K a p itz a ’s c o n fid en ce in h is in g e n io u s a p p ro a c h to his a -ra y p ro b le m s w as ju stifie d b y th e su ccessfu l re su lts he o b ta in e d so q u ick ly . T h is m a d e R u th e rfo rd all th e m o re read y to a c ce p t K a p itz a ’s p e rsu a siv e a rg u m e n ts a b o u t th e p o te n tia l im p o rta n c e o f h ig h m a g n e tic fields a n d low te m p e ra tu re s a n d to give his full b a c k in g in d e v e lo p in g a new b ra n c h of p h y sic s o u tsid e his o w n field.
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