INTRODUCTION. XXXlli 
with scales, 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 seale, 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 
Micrometer| Scale. | Micrometer] Divisions || Micrometer| Scale. | Micrometer] Divisions 
Head. Head. in 60’. Head. Head. in 60’. 
Mie. Div. | Mie. Div. Mic. Div. Mice. Div. Mic. Div. Mic. Div. 
16-5 | 614-5 598-0 16-0 613-8 597-8 
116-5 714-5 598-0 116-0 713-9 597-9 
216-3 813-9 597-6 2151 813-4 598-3 
316-0 913-5 597-5 314-8 913-1 598-3 
416-0 1013-4 597-4 414.4 1013-0 598-6 
515-7 1113-0 597-3 514-3 1112.7 598-4 
Mean value of 1 Division, Left Micrometer, : i 071004 
wes Right ae : ‘ : 071003 
Another Series, August 30. 1841. 
Left Hand Micrometer. Right Hand Micrometer. 
Reading of Reading of | Micrometer Reading of Reading of | Micrometer 
Micrometer Micrometer} Divisions Micrometer Micrometer| Divisions 
Head. Head. in 40’. Head. Head. in 40’. 
Mic. Div. Mic. Div. Mic. Div. Mie. Div. Mic, Div. 
19-0 417-8 398-8 45-0 446-7 
117-5 517-4 399-9 | 145-2 547-1 
216-2 616-9 400-7 246-6 647-3 
319-1 716-3 397-2 | 345-0 747-8 
19-5 418-8 399-3 44-9 446-3 
117-4 518-2 400.8 145-9 547-6 
217-0 j 616-7 399-7 | 246-0 647.4 
319-4 716-3 396-9 345-9 747-8 
Mean value of | Division, Left Hand Micrometer, p : 071002 
ie 2 Right be : ; 07-0996 
Observations made Nov. 23. 1843, gave a mean value for both Micrometers 
1¢ = 071006; this was joined to the above, and the mean of the whole 14 = 01003 
adopted. 
MAG. AND. MET. OBS., VOL. I. 
2. 
