and  Registering  the  Force  and  Direction  of  the  Wind.       37 
wood  wheel  which  revolves  once  for  every  mile  of  wind.  This 
wheel  has  a  deep  rectangular  groove  cut  round  its  circumference  ; 
in  it  at  one  part  is  placed  an  inclined  plane  or  wedge  of  gentle 
slope  and  square  at  the  end;  as  the  wheel  revolves,  the  pointed 
end  of  the  wedge  goes  first.  The  height  of  the  plane  is  a  little 
less  than  the  breadth  of  the  groove.  Just  beyond  the  wedge,  at 
the  square  end  of  it,  a  little  piece  of  platinum  islet  into  the  bot- 
tom of  the  groove  and  connected  through  the  axis  of  the  disk  to 
a  binding- screw  on  the  base. 
Fixed  on  an  upright  is  a  lever  (shown  broken  in  the  drawing) 
carrying  a  platinum  pin,  which  dips  into  the  groove  and  can 
play  from  side  to  side  of  it.  An  armature  is  attached  to  the 
lever,  and  a  small  electromagnet  is  placed  near  it. 
In  the  registering  instrument  is  an  electromagnet,  whose  ar- 
mature can  slide  up  and  down  in  vertical  guides.  A  bar  passes 
downwards  from  the  armature,  and  terminates  in  a  point  just 
above  the  paper  and  between  the  two  type-wheels.  It  is  kept 
off  the  paper  by  a  spring. 
"When  the  contact-disk  revolves,  the  platinum  dot  travels  for- 
ward till  it  reaches  the  pin  attached  to  the  lever;  a  current  then 
passes  through  both  electromagnets.  In  the  registering  instru- 
ment a  dot  is  made  on  the  paper,  while  the  contact-breaker  mag- 
net draws  the  lever  across  the  groove  and  pulls  it  out  of  contact. 
V\  hen  the  disk  has  nearly  completed  another  revolution  the  pin 
comes  to  the  inclined  plane,  and  is  by  it  pushed  back  across  the 
groove  ready  for  another  contact.  By  this  method  no  work  is 
expended  in  raising  a  weight  or  spring  to  prevent  the  points  re- 
maining in  contact;  each  dot  on  the  paper  thus  represents  one 
mile  of  wind.  Thus  the  time,  force,  and  direction  of  the  wind 
are  printed  side  by  side.  A  specimen  of  the  record  is  shown  in 
fig.  4. 
Instead  of  the  two  papers  coming  out  together  (in  which  case 
the  record  is  hidden  by  the  black  paper  for  two  days  after  being 
printed),  the  black  paper  immediately  after  leaving  the  type- 
wheels  is  carried  upwards  back  over  the  top  of  the  instrument 
and  down  behind  the  reels,  where  it  passes  out  through  a  slot  in 
the  base.  The  papers  are  kept  tight  by  little  weights  attached 
to  their  ends  by  clips. 
I  cannot  conclude  this  paper  without  expressing  my  obliga- 
tions to  Mr.  Apps  for  the  skill  and  care  which  he  has  displayed 
in  the  manufacture  of  the  instrument. 
July  18/1. 
Note  added  November  12,  1871. 
Four  of  these  instruments  have  now  been  made,  two  printing 
and  two  simply  indicating.     They  all  act  exceedingly  well.     Of 
