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An English translation by Tait had recently appeared [Phil. Mag. 33: 485-512] of Helmholtz, H. 1858. Ueber Integrale der hydrodynamischen Gleichungen, welche den Wirbelbewegungen entsprechen. Journal für die reine und angewandte Mathematik 55: 25-55. William Thomson also makes mention of papers from Rankine (1849-50) on "Molecular Vortices". 2 Kragh, H. 2012. Niels Bohr and the Quantum Atom, Oxford University Press, Oxford. 3 Heilbron, J. L. 1981. Historical Studies in the Theory of Atomic Structure, Arno Press, New York. 5 C+( ,#6*'( #07( X#%410&$ H ( 7&'4$*C&'( JK( JK( L"1/'10R'( +18."28%( 7&61.*10( .1( b#QB&%%*#0( &%&4.$17+0#/*4'(#07(."&(/&4"#0*4#%(&."&$K( b1$&16&$9( b#QB&%%R'( %&E#4+( #'( ."&( 6*'*10#$+( 21807&$( 12( ."&( !#6&07*'"( h#C1$#.1$+(*0(!#/C$*7E&(*'(10&(12(."&(/#0+(."$&#7'(."#.(C*07(."&(."$&&(/#*0(#4.1$'( *0( ."&( '.1$+( ."#.( 21%%1B'K( ( L"*'( *'( ."&( -%#4&( B"&$&( L"1/'10( B#'( # 1*0.&7( #'( 7*$&4.1$( *0( G;;H9( B"&$&( N8."&$21$7( B1$F&7( # '( L"1/'10R'( 2*$'.( $&'&#$4"( '.87&0.( 2$1/(G;>](.1(G;>;9(#07(B"&$&()1"$('.1 &7(16&$(*0(G>GG(C&21$&(/16*0E(10(.1(g1*0( N8."&$21$7(#.(."&(50*6&$'*.+(12(b#04"&'.&$K((L"&$&(*'(#0(1%7(#7#E&( . "#.(/1'.(%*0&'(12( $&'&#$4"( *0( /17&$0( -"+'*4'9( B"&0( .$#4&7( C#4F( 2#$( &018E"9( B*%%( &6&0.8#%%+( %&#7( .1( J#/&'( !%&$F( b#QB&%%9( #07( ."*'( *'( 01( %&''( .$8&( B"&0( 7&%6*0E( *0.1( ."&( 1$*E*0'( 12( /&4"#0*4#%(/17&%'(12(."&(#.1/K( , ( 4 Davis, E. A. and Falconer, I. J. 1997. J. J. Thomson and the Discovery of the Electron, Taylor & Francis, London. 6 2, The,mechanical,atoms,of,J.,J.,Thomson( ( 2.1, Rings,of,Saturn,and,ethereal,vortices( ( L"&(*0.$1784.*10(.1(b#QB&%%R'(G;]T(&''#+9(S:0(."&(@.#C*%*.+(12(."&(b1.*10(12( @#.8$0R'( N*0E'9S( 410.#*0'( #( 4104*'&( '.#.&/&0.( 12( ."&( 4&0.$#%( ."&/&( 12( "*'( #0#%+'*'9( C8.(#%'1(."#.(12(#0(&0.*$&($&'&#$4"(-$1E$#/(+&.(.1(41/&(10(/&4"#0*4#%(/17&%'(12(."&( #.1/K( ( SY#6*0E( 21807( #( -#$.*48%#$( '1%8.*10( 12( ."&( &D8#.*10'( 12( /1.*10( 12( #0+( /#.&$*#%( '+'.&/9( .1( 7&.&$/*0&( B"&."&$( #( '%*E".( 7*'.8$C#04&( 12( ."&( /1.*10( *07*4#.&7( C+( ."&( '1%8.*10( B18%7( 4#8'&(#( '/#%%( -&$*17*4( 6#$*#.*109( 1$( #( .1.#%( 7&$#0E&/&0.(12(."&(/1.*10KS(kb#QB&%%(G;]>9(-K(]l( ( L"&( -$*Z&( 41//* &&( 21$( ."#.( +&#$( "#7( #'F&7( *2( ."&( %10E?.&$/( '.#C*%*.+( 12( @#.8$0R'( $*0E'(418%7(C&(&Q-%#*0&7(10(7+0#/*4#%(-$*04*-%&'9(807&$(."&(#''8/ *10(."&+(B&$&( &*."&$('1%*79(%*D8*79(1$(/#7&(8-(2$1/(-#$.*48%#.&(/# &$K((V0(#0'B&$(.1(."*'(4"#%%&0E&9( b#QB&%%('*/8%.#0&18'%+(C$18E".( .1(C&#$(#( 08/C&$(12(/#."&/#.*4#%( .&4"0*D8&'(\*0( -#$.*48%#$9( X18$*&$( #0#%+'*'( #07( h#E$#0E*#0( /&4"#0*4'_( .1( 2*$'.( '"1B( ."#.( #( 80*21$/%+( '1%*7( $*0E( B18%7( C&( &*-"0,!"//*( 1-+#"5/'9 ] ( #07( ."#.( #( %*D8*7( $*0E( /8'.( 8%.*/#.&%+(C$&#F(#-#$.(*0.1(7*'4100&4.&7(7$1-%&.'K( ( L"&($&/#*0*0E(-1''*C*%*.+(B#'(21$(."&($*0E'(.1(C&(41/-$*'&7(12(*07&-&07&0.( -#$.*4%&'(\B"&."&$('1%*7(1$(%*D8*7_9(&#4"(/16*0E(807&$(."&(E$#6*.#.*10#%(*02%8&04&(12( ."&( 4&0.$#%( /#''9( #'( B&%%( #'( ."#.( 12( #%%( ."&( 1."&$( 1$C*.*0E( -#$.*4%&'K( ( b#QB&%%( # $1Q*/#.&7(#('*0E%&(-%#0&.#$+($*0E(#'(#(41%%&4.*10(12(-1*0.(/#''&'(7*'.$*C8 .&7(#.( &D8#%?#0E%&( *0.&$6#%'( #$1807( #( 4*$4%&9( 7&$*6&7( ."&( &D8#.*10'( 12( /1.*10( 21$( .B1( /#''&'( *0( '.#C%&( 1$C*.9( ."&0( '.&-B*'&( %&.( ."&( 08/C &$( 12( '#.&%%*.&'( E$1B( 80.*%( #$C*.$#$*%+( %#$E&K((5-10( 7&.&$/*0*0E( ."&( 4107*.*10'( 21$( '.&#7+?'.#.&( /1.*109( "&( 410'*7&$&7(."&(&22&4.(12(#0+('/#%%(7&6*#.*10(12(."&(-#$.*4%&'(2$1/(."&*$(1$C*.'9(*0(."&( 5 There would be an insufficient restoring force if the centers of mass for the uniform ring and the planet ever deviated from equilibrium, eventually leading the ring and planet to crash into each other. The only exception was most unlikely: an otherwise uniform ring would require an additional point mass located at its outer edge, equal to 0.82 of the mass of the total ring. [Maxwell 1859, p. 55] 7 $#7*#%(#07(.#0E &0.*#%(7*$&4.*10'9(#'(B&%%(#'(-&$-&07*48%#$(.1(."&(-%# 0&(12($1.#.*10K((V2( ."&( /1. *10( 12( ."&( -#$.*4%&'( B&$&( .1( C&( -&$/#0&0.9( ."&( '1%8.*10'( .1( ."&'&( '&.'( 12( 7*22&$&0.*#%(&D8#.*10'(B18%7("#6&(.1(#%%(C&('*08'1*7#%(\."&(-#$.*4%&'(B18%7(1'4*%%#. &( #C18.(."&*$( &D8*%*C$*8/(-1'*.*10'_j(&Q-10&0.*#%( '1%8.*10'( 41$$&'-107&7(.1( ."&($*0E( C$&#F*0E(#-#$.K((L"*'(-%#4&7(C#'*4(410'. $#*0.'(10(."&(-$1-&$.*&'(12(."&('+'.&/(^(/1'.( 01.#C%+9(."&(/#''(12(."&(4&0.$#%(C17+(B18%7("#6&(.1(C&('8C'.#0.*#%%+(%#$E&$(."#0(."&( '8/(12(."&(1$C*.*0E(/#''&'K(kb#QB&%%(G;]>9(-K(W]l( ( L"&(*02%8&04&(12(b#QB&%%(*'($&#7*%+(# #$&0.(*0(L"1/'10R'(1B0(G;;W(A7#/'( 3$*Z&(&''#+K((L"*'(.*/&9(."&(41//* &&("#7(4#%%&7(21$(#(SE&0&$#%(*06&'.*E#.*10(12(."&( #4.*10(8-10( &#4"( 1."&$(12( .B1( 4%1'&7(61$.*4&'( *0( #(-&$2&4.( *041/-$&''*C%&(2%8*79S(#( .1-*4( ."#.( B#'( 12( 48$$&0.( *0.&$&'.( .1( /#."&/#.*4#%( -"+'*4*'.'9( - # $.*48%#$%+( '*04&( b#QB&%%( "#7( 7&'4$*C&7( X#$#7#+R'( /,-'+( %6( 6%)!'( *0( .&$/'( 12( 61$.*4&'( *0( #0( &%&4.$1/#E0&.*4(/&7*8/K [ ((L"&(2807#/&0.#%('*/-%*4*.+(12(i&%6*0R'(/1$&($&4&0.(*7&#'( # &#%&7( .1( JK( JK( L"1/'109( ."#.( #%%( ."&( 6#$*18'( -$1-&$.*&'( 12( /#.&$*#%'( /*E".( C&( &Q-%#*0&7(*0(.&$/'(12(."&(7+0#/*4'(12(&."&$&#%(61$.*4&'K( ( SL"&(&D8#.*10'(B"*4"(7&.&$/*0&7(."*'(/1.*10(B&$&(F01B0(2$1/(."&(%#B'(12( "+7$17+0#/*4'9('1(."#.(*2(."&(."&1$+(B&$&( .$8&(."&('1%8.*10(12(."&(-$1C%&/(12( ."&( 80*6&$'&( B18%7( C&( $&784&7( .1( ."&( '1%8.*10( 12( 4&$.#*0( 7*22&$&0.*#%( &D8#.*10'9( #07( B18%7( C&( &0.*$&%+( #( /# &$( 12( 7&6&%1-*0E( /#."&/#.*4#%( /&."17'( -1B&$28%( &018E"( .1( 7&#%( B*."( B"#.( B18%7( 01( 718C.( C&( 6&$+( 41/-%&Q(7*'.$*C8.*10'(12(61$.&Q(/1.*10(*0(."&(2%8*7K(knl(L"&(*06&'.*E#.*10(n( *061%6&7(%10E(#07(41/-%*4#.&7(/#."&/#.*4#%(#0#%+'*'(#07(.11F(#(%10E(.*/&K( (V.( +*&%7&79( "1B&6&$9( '1/&( *0.&$&'.*0E( $&'8%.'( #07( *7&#'( B"*4"( V( #2.&$B#$7'( 21807(6#%8#C%&(*0(4100&4.*10(B*."(."&(."&1$+(12(."&('.$84.8$&(12(."&(#.1/nS( kL"1/'10(G>=[9(-K(>H?]l( ( ( L"&(2*$'.(.B1(-#$.'(12(L"1/'10R'(&''#+(7&#%.(B*."(."&(/#."&/#.*4'(7&'4$*C*0E( #('*0E%&(61$.&Q(*0(#0(*7&#%(2%8*79(#07(."&0(.B1(61$.*4&'('&-# $#.&7(C+(#(7*'.#04&(%#$E&( 41/-#$&7( .1( ."&*$( $#7**9( B"*4"( #%10&( /*E".( "#6&( C&&0( '822*4*&0.( .1( '#.*'2+( ."&( 6 Maxwell 1861, p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kL"1/'10(G;;=#9(-K(G<T?;l( ( )&+107( /#."&/#.*4#%( &Q-&7*&04+9( L"1/'10R'( 4"1*4&( .1( B1$F( B*."( '+//&.$*4#%%+(7*'.$*C8.&7(61$.*4&'(418%7(C&(-"+'*4#%%+(/1.*6#. &7(B*."(#0(#0#%1E+(.1( ."&('.#.*4(#$$#0E&/&0.'(12(2%1#.*0E(/#E0&.'(807&$(."&(*02%8&04&(12(#(4&0.$#%(21$4&9(#'( $&-1$.&7(C+(A%2$&7(b# +&$(*0(G;T;K((b#+&$("#7('.84F(/#E0&.*Z&7(0&&7%&'(*0.1(-*&4&'( 12( 41$F( B*."( ."&( '18."( &07'( -1*0.*0E( 8-B#$79( '1( ."#.( ."&+( B&$&( #%%( /8.8#%%+( $&-&%%&79(C8.(&#4"(# $#4.&7(.1( ."&(01$."(&07( 12(#(C#$(/#E0&.(-%#4&7(#.(."&(4&0.&$K(( L"*'( 41/C*0#.*10( 12( -8'"( #07( -8%%( 4#8'&7( ."&( 2%1#.*0E( 0&&7%&'( .1( $&#$$#0E&( ."&/'&%6&'(*0.1($&E8%#$(-1%+E10'9(g8'. (%*F&(L"1/'10R'(61$.*4&'K(kX*EK(Gl(P*."(-(o(]9( #7%('.#.*4(#$$#0E&/&0.'(B&$&(-1''*C%&I(#(-&0.#E10(k]#l(#07(#('D8#$&(B*."(#(0&&7%&( #.(."&(4&0.&$(k]Clj(C8.(10%+(."&(-&0.#E10(B#'('.#C%&(#E#*0'.(&Q . &$0#%(-&$.8$C#.*10'K(( @.#.*4( $*0E'( 12( '*Q9( '&6&0( #07(/1$&( B&$&( -1''*C%&( B*."( #77*.*10#%( *0.&$*1$( 0&&7%&'9( B"*4"( ."&/'&%6&'( '& %&7( *0.1( '.#C%&( -# &$0'( #'( ."&*$( 08/C&$'( E$&B( \*K&K9( ."&( 4102*E8$#.*10(21$(]#(418%7(21$/(."&(41$&(12(-(o(GH9(B"&$&#'(]C(418%7(01._K(kb#+&$9((( -K(W]Gl(b#+&$("*/'&%2(."18E".(."&'&('*/-%&($8%&'(/*E".(-$16*7&(*0'*E". (*0.1(6#$*18'( /1%&48%#$(-$1-&$.*&'(\'84"( #'("//%#)%2*( #07(,+%0'),+0_9(C8.( *.(B#'(."&( 28.8$&(h1$7( i&%6*0( B"1( 2*$'.( /#7&( ."&( 4100&4.*10( C&.B&&0( ."&( '.#.*4( 4102*E8$#.*10'( 12( ."&( /#E0&.'(#07(."1'&(21$(61$.&Q(#.1/'(*0(#('.#.&(12(/&4"#0*4#%(&D8*%*C$*8/K T ( ( 7 Thomson, W. 1878. Floating Magnets. Nature 17: 13-14. 9 ( ( Figure 1. Static arrangements for n = 2 – 20 floating magnetic needles (all with their south poles oriented vertical), under the attractive influence of a central bar magnet. If multiple static configurations were possible for a given n, only those denoted by an "a" were stable against perturbations. [From Mayer, p. 248-9]( ( ( ( ( JK(JK(L"1/'10(#%'1(8'&7("*'(61$.&Q(/17&%(.1(&Q-%#*0(."&(4"&/*4#%(41/C*0#.*10( 12( &%&/&0.'9( C+( #''14*#.*0E( ."&( 08/C&$( 12( 2),0")*( 61$.*4&'( *0( #0( #.1/( B*."( *.'( 6#%&04+(\&#4"(-$*/#$+(61$. &Q (418%7(g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kL"1/'10(G;;=#9(-K(GW<?WGl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b# Q B&%%R'(01.*10(12( #0(&."&$&#%(&,+2/"!'0'-#(!1))'-#_K(kL"1/'10(G;;=C9(-K(HW;?W>l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g&4.1$*&'( C+( #(/#E0&.*4( 2*&%7( '"1B&7( ."#.( ."&+( B&$&( 01.( %*F&(((( p?$#+'9( C8.( $#."&$( "*E"( 6&%14*.+9( 0&E#.*6&%+( 4"#$E&7( R41$-8'4%&'R( 12( /# &$K( kL"1/'109(G;>Tl( ( ( 2.2, A,corpuscular,theory ,of,ma tter( ( `A2.&$(%10E(410'*7&$#.*10(12(."&(&Q-&$*/&0.'(*.('&&/&7(.1(/&(."#.(."&$&(B#'( 01(&'4#-&(2$1/(."&(21%%1B*0E(4104%8'*10'I(\G_(L"#.(#.1/'(#$&(01. (*07*6*'*C%&9( 21$( 0&E#.*6&%+( &%&4.$*2*&7( -#$.*4%&'( 4#0( C&( .1$0( 2$1/( ."&/( C+( ."&( #4.*10( 12( &%&4.$*4#%( 21$4&'9( */-#4.( 12( $#-*7%+( /16*0E( #.1/'9( 8%.$#6*1%&.( %*E".( 1$( "&#.K((( 8 His first conceptions were in analogy with electrolysis. [Davis and Falconer, p. 77-8; see also p. 77-138 for details on the evolution in Thomson's thinking about gaseous discharge leading up to his discovery of the electron.] [...]...   deflection   ϕ1   due   to   a   uniform   sphere   of   positive   charge   would   be   directly   proportional to  N0  (the  number  of  charges  in  a  neutral  atom),  whereas  ϕ2  and  θ1  are   both  proportional to   N 0    This  implies –  for  atoms  with  a  large  value  of  N0 –  that   the  dominant  contribution to  the  total  scattering  would  be from  the  positive  sphere,... different atoms, from the inner rings (upper rows) to the outer rings (lower rows), where N represents the total number of charges in each atom The N = 3, 11, 24, 40 & 60 atoms would form a single vertical column in the Periodic Table, each member of the group derived from the previous member by the addition of a single ring [Adapted from Thomson 1904, p 257.]     In  a  similar  vein,  atoms  in  the... charges from inner rings (top rows) to outer rings (bottom rows) for the group of atoms containing N = 59 – 67 charges Each has 20 charges in its outermost ring, placing them all in a single horizontal row of the Periodic Table [From Thomson 1904, p 258]     With   additional   interior   charges,   successive   atoms   in   this   group   would   be   less  and  less  electropositive,21  eventually to. ..  no  choice  but to  concoct  a  hypothetical  smear   of   positive   atomic   charge,   which   he   likened   (crudely)   to   "a   liquid   with   a   certain   amount  of  cohesion,  enough to  keep  it from  flying to  bits  under  its  own  repulsion."10     Thomson   never   believed   in   the   literal   truth   of   his   mechanical   analogies,   and   preferred   to   de-­‐emphasize...   single   atomic   encounter   was   directly   proportional   to   the   atomic   weight   A     To   do   this,   he  defined   a   scattering   coefficient   K   as   the   most   probable   deflection   angle   for   a   thickness   of   material   with   stopping   power   equivalent   to   one   centimeter   of   air     Geiger   claimed   that   K   should   be   proportional   to   the  ...  inside  a  fixed  angle  ϕ,  which   he   then   used   to   calculate   the   total   number   of   charges   per   atom   N0   according   to   both   of  Thomson’s  proposals  [Table  V]     Assuming   the   positive   charge   to   be   uniformly   distributed   in   a   sphere   of   atomic   radius   (Theory   A)   resulted   in   a   nearly   constant   value   for   all   the   scattering... [Crowther, p.229-33] 25 “…the  positive  electricity  in  an  atom  is  not  in  a  state  comparable to  that  of  the   electron,  but  …  occupies  such  comparatively  large  volumes  as to  be  capable   of   being   considered   as   uniformly   distributed   over   the   whole   atom.”   [Crowther  1910,  p  240]     N 0   N 0 Atomic weight   Atomic   φ t m   weight   A   B   A   B   Carbon*... 1908a, p 156] 30 had to  be  an  integral  multiple  of  the  fundamental  unit,  the  evidence  was  strongly  in   favor   of   the   former   over   the   latter,   in   particular   because   a   charge   of   2e   would   correspond   to   the   α-­‐particle   having   an   atomic   weight   of   3.84,   very   close   to   the   atomic  weight  of  helium  at  3.96     “Taking  into  account  probable... according   to   the   atomic   weight   of   the   reflector   [Geiger   and   Marsden,  p  495-­‐7;  see  Table  VII]       Figure 6 Setup used by Geiger and Marsden to study the reflection of α-particles from a metal surface The lead plate P is situated between the α-source AB (an active glass tube) and the detecting screen S (observed with microscope M) The only path from source to detector was by reflection... increases with the increasing atomic weight of the scatterer The anomalous data for lead was attributed to suspected impurities in the metal [From Geiger and Marsden, p 497] 1  Metal   2 Atomic  weight,   A   34 They  next  found  that  the  number  of  scintillations  they  observed  depended  on   the   thickness   of   the   reflector,   in   a   way   that   was   similar   to   reflection   experiments . 1 Early Atomic Models – From Mechanical to Quantum (1904-1913) !"#$%&'()#*%+( ,&-#$./&0.(12(3"+'*4'( 50*6&$'*.+(12(!1%1$#71( )18%7&$9(!:(;<=<>?<=><9(5@A( ( Abstract( ( A(. continued to refer to negative atomic charges as “corpuscles” throughout the article, and for many years after. George Stoney claimed in 1894 to have coined