288 REPORT— 1851. 



4"'988 

 and — — — =0"4157=timeof one division of large dial or of one revolution 



of small, and — — — -=0"-01386; which differs from the preceding rating 



30 

 by first experiment only by 2 in the fifth decimal place. 



The same mode of rating was applied to Sharp's (the Observer's) chrono- 

 graph, on the 21st of October IB^Q,. thus : — 



Wound up 5 revolutions in every case. 



Rejecting experiments 4 and 5 therefore as probably inaccurate from the pre- 

 cise accordance of the others, we may take the time as 5 rev.=25"-00, and 



nrll 5" 



— =5"-00 time of one revolution of large dial and — -=0"'4166=value of 

 5 ° 12 



0"*4166 

 one division of large dial=l revolution of small, and therefore — 



30 



=0"'013887=value of one division of small dial. 



These determinations were made for the experiments which were found 

 abortive on the 25th of October 1849, and as it then became necessary to 

 bring both chronographs into town and alter their attachments, it Avas re- 

 quisite again to rate them before proceeding with the next trials ; this was 

 done as follows : — 



Wheatstone's Chronograph, 29th of October 1 849. 

 Seven revolutions ran down in all cases. 



// 

 Exp. 1. 7 revolutions made in 35-50 



2. 7 „ » 35-75 



3. 7 „ „ 36-00 



4. 7 » ,, 36-00 



5. 7 » „ 36-00 



6. 7 „ „ 36-00 



7. 7 „ „ 36-00 



8. 7 „ „ 36-00 



9. 7 ,, „ 36-00 



Rejecting experiments 1 and 2 as probably incorrect observations, we have 

 the time of 7 revolutions=36" or -— =5"-14286=time of one revolution 



of large dial, and therefore ^-l^M§^=o"-42857=time of one division of 

 o 12 



0"-42857 

 large dial=one revolution of small hand, therefore — =0"-014206 



= the time of one division of small dial. 



The rating of Sharp's chronograph was now performed by both the old 

 and new methods, as it was to be used at the observing end of the line, and 

 the utmost accuracy was there desirable. 



