XXXVI INTRODUCTION. 
42. Vibration of the balance magnet in the vertical plane. 
The needle being in its usual position on the supports, the moveable wire of 
the left micrometer is made to bisect the spider cross ; the needle is then vibrated, 
by means of a small piece of iron, through an angle, varying from 10/ to 5’, and the 
periods of the cross passing the wire estimated. 
TABLE 16.—Values of T, the Time of Vibration of the Balance Needle in a Vertical Plane. 
Time of one Vibration. 
Number Adopted 
Date. of Mean. Remarks. 
Vibrations.) Observed. Adopted. 
a h 8. 3. 8. 
1841. 
July 6 0 10 10-72 10-60 10-6 
Adjustment, &c., after July 23°. 
Aug. 3 4 48 10-25) 
10-04 10-0 
Aug. 3 4 54 10-17 —_______|| {August 30°. Agate planes adjusted, and 
spider’s lines inserted instead of silver wires. 
Sept. 4 5 || 36 10-83 
Sept. 4 5 84 10:69 + 10-63 
Sept. 4 5 96 10-61 10-6 
Sept.27 5 || 44 10-69 get 
Sept. 27 5 66 aes aes 
Oct. 2° 24, Needle reversed to determine 
Oct. 2 4 42 11-07 11-06 the deviation of the crosses. 
Oct. 2 4 54 11-09 
Oct. 16 4 || 56 11-08 ae 
Oct. 16 4 34 11-03 11-0 
Oct. 29 4 50 11-03 11-00 
Nov. 20 3 80 10-99 10-97 
Dec. 3 4 18 11-00 
Dec. 3 4 60 eat igs 
1842. 
Jan. 1°, &c. Needle removed in order to 
Jan. 15 5 38 10-70 10-66 10-6 determine its temperature correction. 
Jan. 29 5 46 10-32 10-30 
Hebe 12 5 30 10 15 
Feb, 12 5 | 57 HA LOS 
Mar. 5 6 63 10-34 10-32 10-1 
Mar. 19 5 48 10-15 
Mar. 19 53) 42 eee roe 
March 22°. Needle vibrated excessively 
Apr. 2 6] 68 11-02 10-96 by iron brought near it by visitors. 
Apr. 9 5 56 10-94 10-94 11-0 
Apr. 16 0 60 11-02 10-96 
Apr. 23 0 36 10-77) 
Apr 23 0 36 10-72> 10-64 
Apr. 23 0|| 30 10-82 
June 20 6 50 10-65 
June 20 6 40 eel a 
June 25 8 30 10-58) 
June25 8|| 50 10-59) AUS 
July 16 6 50 10.46 10-42 10-5 
