43.  APRIL  1872.  No.  286. 
Published  the  First  Day  of  every  Month. — Price  2s.  6d. 
THE 
LONDON,  EDINBURGH,  and  DUBLIN 
JPHILOSOPHICAL     MAGAZINE, 
AND 
JOURNAL  OF  SCIENCE. 
Being   a    Continuation   of  Tilloch's    'Philosophical   Magazine/ 
Nicholson's  'Journal/  and  Thomson's  'Annals  of  Philosophy.3 
CONDUCTED  BY 
SIR  ROBERT  KANE,  LL.D.  F.R.S.  M.R.I.A.  F.C.S. 
SIR  WILLIAM  THOMSON,  Knt.  LL.D.  F.R.S.  &c. 
AND 
WILLIAM  FRANCIS,  Ph.D.  F.L.S.  F.R.A.S.  F.C.S. 
FOURTH    SERIES. 
N°  286.— APRIL  1872. 
LONDON: 
PEINTED  BY  TAYLOE  AND  FEANCIS,  EED  LION  COUET,  FLEET  BTEEET, 
Printers  and  Publishers  to  the  University  of  London. 
Sold  by  Longmans,  Green,  Reader  and  Dyer ;  Kent  and  Co. ;    Simpkin,  Marshall  and 
Co. ;  Whittaker  and  Co. ;  and  H.  Bailhere,  London  :— and  by  A.  and  C.  Black,  and 
Thomas   Clark,  Edinburgh;     Smith  and   Son,  Glasgow: — Hodges    and    Smith, 
Dublin  : — Putnam,  New  York  : — and  Asher  and  Co.,  Berlin. 
