32      Mr.  J.  E.  Gordon  on  a  new  Anemometer  for  Indicating 
abstract  of  it  will  appear  in  the  '  Report '  for  1871.  My  reason 
for  publishing  it  in  ewtenso  at  the  present  time  is  that  I  propose 
to  make  use  of  the  results  relating  to  the  variations  of  atmo- 
spheric pressure  due  to  the  moon's  attraction  in  a  discussion  of 
the  hydrodynamical  theory  of  magnetism,  and  was  desirous  of 
previously  exhibiting  the  mathematical  reasoning  by  which  the 
results  are  obtained.  In  my  work  on  the  Principles  of  Ma- 
thematics and  Physics  (pp.  662-665),  I  have  attempted  to  ac- 
count for  the  lunar  diurnal  variation  of  terrestrial  magnetism 
by  attributing  it  to  the  gradations  of  the  pressure  of  the  earth's 
atmosphere  caused  by  the  moon's  gravitation ;  but  at  that  time 
I  was  not  acquainted  with  the  proper  method  of  ascertaining 
theoretically  the  laws  of  the  moon's  disturbance  of  the  atmo- 
sphere. This  problem  having  been  subsequently  solved  by  the 
method  explained  in  this  communication,  I  then  found  that 
the  resulting  laws  and  amount  of  the  variation  of  the  atmo- 
spheric pressure  fail  to  account  for  the  observed  laws  of  lunar 
diurnal  variation  of  magnetism.  The  consequent  necessity  of 
abandoning  this  mode  of  explaining  the  phenomena  has  led  to 
a  considerable  modification  of  the  views  contained  in  the  same 
work  (pp.  670-676)  respecting  the  causes  of  cosmical  magnetism, 
the  particular  reasons  for  which  I  hope  to  be  able  shortly  to  ex- 
plain in  the  course  of  a  general  review  of  the  Hydrodynamical 
Theory  of  Magnetism. 
Cambridge,  December  8,  1871. 
IV.  Description  of  a  new  Anemometer  for  Indicating  and  Regis- 
tering the  Force  and  Direction  of  the  Wind  at  any  distance  from 
theVane,  fyc,  the  communication  being  made  by  means  of  Elec- 
tric Wires  and  without  the  aid  of  Shafting.  Invented  by  J.  E. 
H.  Gordon,  late  of  King's  College,  London*. 
[With  a  Plate.] 
THE  object  of  this  instrument  is  to  do  away  with  the  neces- 
sity of  the  shaft  hitherto  required  for  anemometers  indi- 
cating at  a  distance.  Several  anemometers  for  communicating 
force  by  electricity  have  been  invented  in  the  last  year  or  two ; 
but  this  is,  I  think,  the  first  time  that  direction  also  has  been 
communicated  and  printed  by  the  electric  current  f. 
*  Communicated  by  the  Author. 
f  Since  the  above  was  in  type  the  Rev.  S.  J.  Perry  has  had  the  kind- 
ness to  send  me  a  description  of  Padre  Secchi's  Meteorographe,  which  con- 
tains an  electrical  anemometer.     In  this  (to  quote  Padre  Secchi's  descrip- 
tion)»  .      ,  ,y 
.  ..."  La  direction  du  vent  est  enregistree  par  quatre  telegraphes. 
Elle  est  obtenue  au  moyen  d'une  girouette  a  la  prouede  laquelle  on  donne 
une  forme  angulaire  afin  de  diminuer  les  oscillations.    Au  pied  de  la 
