AND ITS TEMPERATURE CORRECTION. 71 
The following short series, taken at random from a great number of observa- 
tions, at once prove the truth of this conclusion. From a comparison of a few of 
the observations, it was found that an increase of 1° Fahr. was equivalent to an 
increase of 0.076 in the time of vibration. 
The last column for each series gives the times corrected by this quantity to 
50° Fahr. That the correction obtained is only approximate, will, together with 
errors of observation, account for much of the discrepancies in the corrected 
quantities. 
TABLE III. 
Observations for the Time of Vibration of the Balance Needle in the Vertical 
Plane at different Temperatures. 





















é Time of . Time of 
Time of Observed time | Temperature BnolVabeation Time of posersed time Temperature BHOnURbration 
Observation. | yitration. Magnet Bee eae  ObReRERiton Vibration. Wiseatcts per a 
Geb May 8 ) s s ° 8 
Jan. 2 22 8.91 31.4 10.32 (eal 35.4 8.32 
3 2 9.48 40.0 10.24 8.38 46.3 8.66 
3°44 9.80 43.5 10.29 7.42 35.9 8.49 
3) 9%) 9.96 45.2 10.32 6.72 27.0 8.47 
3 22 9.74 41.4 10.39 6.42 21.5 8.59 
7.64 38.7 8.50 
April 30 22 8.97 6.93 32.6 8.25 
May 1 8 SHCULEg 64.1 8.70 7.49 38.9 8.33 
1 22 9.28 56.3 8.80 
2 21 9.13 55.2 8.73 9 22 7.43 41.0 8.11 
3.8 9.81 64.4 8.72 12 23 6.87 31.6 8.27 
3 23 9.02 53.6 8.75 13 22 7.08 31.9 8.46 
16 22 6.82 31.2 8.25 
23 23 8.07 45.6 8.40 
April 1 11 8.10 8.20 


It should be remarked, that the series for January 1844 is not comparable 
with the following series, as an adjustment of the instrument occurred in that 
month; neither, indeed, are the other series comparable with each other, from the 
circumstances given in Table I. 
7. To take one of the most marked cases from this table, it will be seen that 
the observed times of vibration on January 23d and 31st 1845, differ nearly two 
seconds, while the corrected times do not differ one-tenth of a second. 
8. While an inequality in the expansion of some parts of the needle would 
alter its sensibility by elevating the centre of gravity, it seems very doubtful 
if there is any thing in the form of the needle which is at all likely to render 
this supposition sufficient. An alteration in the position of the centre of motion 
would produce a like effect; and as the position of the needle depends, to some 
extent, on its temperature, it is necessary to shew whether position or tempera- 
ture only is the cause of the differences in the times of vibration. Had the read- 
ings for the position of the needle been given with Table IIT., it would have been 
evident from these alone that the differences were not due to differences of posi_ 
