394 
Mr.  Mond  and  Dr.  Wilderman 
on  a 
-with  writing-pens,  we  keep  them  all  stationary  and  only 
move  the  light  spindle  with  the  writing-pen,  thus  diminishing 
the  load  upon  the  clock  arising  from  the  work  transmitted  by 
the  clock.  (2)  We  reduce  the  friction  of  the  different  parts 
in  motion  to  that  of  the  moving  spindle  only,  and  further 
reduce  that  by  the  use  of  friction  wheels  or  balls,  &c.  (3)  We 
avoid  the  reactions  of  inertia,  as  far  as  possible,  by  a  perfect 
balance  of  the  moving  part  of  the  instrument — the  spindle. 
Experiments  for  several  years  showed  the  intricacy  and  the 
minuteness  of  conditions  to  be  carried  out  simultaneously  in 
the  construction  of  a  chronograph  for  high  speeds  before  a 
satisfactory  result  could  be  obtained.  We  shall  for  this 
reason  describe  and  explain  all  those  details  upon  which  the 
successful  construction  and  use  of  our  chronograph  depends. 
Figure  I.  (k  PI.  VIII.  fig.  1)  represents  a  horizontal  type  of 
our  chronograph,  as  made  for  us  by  Messrs.  Sanger,  Shepherd 
and  Co.  d  is  the  driving  clock,  a  is  the  stationary  drum  60  cm. 
circumference  fixed  (in  exact  horizontal  position)  to  the 
bracket  (C).  The  horizontal  spindle  (/)  carrying  the  pen- 
arm  (]i)  of  the  writing-pen  (c)  and  the  electromagnet  (i)  is 
counterbalanced  by  the  nut  (v)  which  is  adjustable  on  the 
screw  (?<).  The  horizontal  spindle  passes  at  one  end  through 
the    boss  of  a  pinion  wheel  (K),  driven    by  the  wheel  (l) 
