New  Improved  Type  of  Chronor/rapJi.  395 
of  the  clock,  thus  describing  a  circle  round  the  drum.  A 
strip  projecting  from  the  spindle  forms  a  long  feather,  and  a 
corresponding  featherway  in  the  boss  of  the  pinion,  2  mm. 
wide,  renders  the  spindle  capable  of  axial  movement  with 
regard  to  the  pinion,  caused  by  the  screw  of  the  spindle  (/') 
and  the  half-nut  (S),  fixed  to  the  drum  and  insulated  from 
the  same  by  means  of  the  ebonite  strip.  Owing  to  this 
double  action  of  the  spindle,  the  writing-pen  describes  a 
spiral  on  the  drum.  The  instrument  shown  in  fig.  I.  gives  a 
spiral  50  x  60  =  3000  cm.  long,  the  circumference  of  the 
drum  being  60  cm.  Since  the  writing  pen  can  easily  make 
one  revolution  per  minute  or  in  10  seconds,  we  have  10  mm. 
or  60  mm.  for  registration  of  one  second.  The  line,  of  our 
pen  being  very  thin,  we  can  read  well  to  0'2  mm.  or  even 
less,  i.  e.  1/50  or  1/300  of  a  second,  provided,  however,  means 
are  found  to  make  electrical  contacts  to  the  same  degree  of 
accuracy ;  a  problem  which,  it  seems  to  us,  will  give  much 
trouble  if  a  conscientious  scientific  investigation  should  be 
properly  attempted.  Since  in  our  type  of  chronograph  the 
drum  is  stationary  and  a  great  extension  in  its  height  and 
width  means  only  an  extension  of  the  length  of  the  arm  of 
the  spindle,  which  means  only  a  small  increase  of  load  and 
almost  no  increase  in  the  friction  or  the  reaction  of  inertia, 
we  are  thus  able  to  construct  instruments  with  still  greater 
length  of  spiral  and  of  the  same  accuracy. 
The  boss  of  the  spindle  rests  on  two  little  friction  wheels  (w) 
fixed  to  the  support  (o),  and  is  kept  in  position  by  the  slight 
exterior  circumferential  groove  on  the  boss  with  which  the 
friction  wheels  engage  ;  the  friction  of  the  spindle  at  this 
end  is  thus  reduced  to  two  points  only.  The  screw  end  of 
the  spindle  has  only  to  guide  the  pen  which  writes  with 
almost  no  friction  (the  spindle  must  be  naturally  placed 
exactly  in  the  centre  of  the  drum).  It  is  made  thin  for  this 
reason,  and  the  half-nut  (s)  contains  only  a  little  more  than  a 
line  of  the  thread  just  sufficient  to  move  the  spindle  securely 
forward.  In  this  manner  the  friction  at  this  end  of  the 
spindle  was  also  reduced  to  the  smallest  possible  amount. 
It  will  be  perceived  that  the  wheel  (K)  is  not  fixed  to  the 
spindle.  This  enables  us  to  exchange  without  trouble  one 
pair  of  wheels  for  another  giving  a  smaller  or  greater  speed 
(say  one  revolution  of  the  spindle  in  one  minute  or  in  ten 
seconds),  so  as  to  get  the  speed  which  is  most  suitable  for  the 
investigation  of  the  given  physical,  physico-chemical,  physio- 
logical or  meteorological  phenomenon,  &c.  To  allow  of  the 
use  of  the  exchange  wheels  an  adjustable  fly  is  provided  for 
the  instrument. 
2D  2 
