Inteoduction. 



XXXlll 



with scale?, at the same distance from the centre as the spider's crosses in the mag- 

 net, and graduated to 10', was placed on the agate planes of the support, and the 

 moveable wires brought to coincide with the graduated lines of the scale, the mi- 

 crometer heads being read at each coincidence. 



Table 13. — Determination of the value of one division of the Micrometer Heads 

 of the Balance Magnetometer, June 21. 1841. 



Left Hand Micrometer. 





Right 



Hand Micrometer. 







Reading of 





Reading of 



Micrometer 





Reading of 





Reading of 



Micrometer 



Scale. 



Micrometer 



Scale. 



Micrometer 



Divisions 



Scale. 



Micrometer 



Scale. 



Micrometer 



Divisions 





Head. 





Head. 



in 60'. 





Head. 





Head. 



in 60'. 



' 



Mic. Div. 



' 



Mic. Div. 



Jlic. Div. 



' 



Mic. Div. 



' 



Mie. Div. 



Mic. Div. 







16-5 



60 



614-5 



598-0 







16-0 



60 



613-8 



597-8 



10 



1165 



70 



714-5 



5980 



10 



116-0 



70 



713-9 



597-9 



20 



216-3 



80 



813-9 



597-6 



20 



215-1 



80 



813-4 



598-3 



30 



316-0 



90 



913-5 



597-5 



30 



314-8 



90 



9131 



598-3 



40 



4160 



100 



1013-4 



597-4 



40 



414-4 



100 



1013-0 



598-6 



50 



515-7 



110 



11130 



597-3 



50 



514-3 



110 



1112-7 



598-4 



Mean value of 1 Division, Left Micrometer, 



Right 



0'-l004 

 0'-1003 



Another Series, August 30. 1841. 





Left Hand Micrometer. 







Right 



Hand Micrometer. 







Reading of 





l^eading of 



Micrometer 





Reading of 





Reading of 



Micrometer 



Scale. 



Micrometer 



Scale. 



Micrometer 



Divisions 



Scale. 



Micrometer 



Scale. 



Micrometer 



Divisions 





Head. 





Head. 



in 40'. 





Head. 





Head. 



in 40'. 



' 



Mic. Div. 



' 



Mic. Div. 



Mic. Div. 



/ 



Mic. Div. 



/ 



Mic. Div. 



Mic. Div. 







19-0 



40 



417-8 



398-8 







45-0 



40 



446-7 



401.7 



10 



117-5 



50 



517-4 



399-9 



10 



145-2 



50 



547-1 



401-9 



20 



216-2 



60 



616-9 



400-7 



20 



246-6 



60 



647-3 



400-7 



30 



319-1 



70 



716-3 



397-2 



30 



345-0 



70 



747-8 



402-8 







19-5 



40 



418-8 



399-3 







44-9 



40 



446-3 



401-4 



10 



117-4 



50 



518-2 



4008 



10 



145 9 



50 



547-6 



401-7 



20 



217-0 



60 



616-7 



399-7 



20 



246-0 



60 



647-4 



401-4 



30 



319-4 



70 



716-3 



396-9 



30 



345-9 



70 



747-8 



401-9 



Mean value of 1 Division, Left Hand Micrometer, 



Kiaht 



0'-1002 

 0'-0996 



Observations made Nov. 23. 1843, gave a mean value for both Micrometers 

 \^ = 0'-1006; this was joined to the above, and the mean of the whole 1*^ = 0^-1003 

 adopted. 



