.  43.  MAY  1872.  No.  287, 
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°  287.— MAY  1872. 
LONDON: 
PBINTED  BY  TAYLOB  AND  FRANCIS,  BED  LION  COTTBT,  FLEET  STBEET, 
Printers  and  Publishers  to  the  University  of  London. 
Jold  by  Longmans,  Green,  Eeader  and  Dyer ;  Kent  and  Co. ;   Simpkin,  Marshall  and 
I   Co.;  "Whittaker  and  Co. ;  and H.  Bailliere, 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. 
