76 MR BROUN ON THE BALANCE MAGNETOMETER, 
The differences, when ¢,>t,,, were too irregular and too few, on some days, 
to give a good value of a. 
17. It is very rare that periods of such magnitude can be found free from 
considerable irregularities. In general, however, it is conceived that smaller pe- 
riods will give equally good results, and by a shorter method. 
If we consider the equations 
_ Yo — Yprr ra 
=e ae a EY 
Se dy te ds 5p eee ae 
Ynrr— 4 ra 
q — Yor Yp de : fy tees 
lpr 3 b lor = tp 
it is obvious, that if the temperatures rise and fall considerably throughout the 
period selected, and no attention be paid to the sign of ¢,—¢,,, in the summations 
of the differences, the coefficients of a will nearly destroy each other. 
18. In the following cases the sums for each day have been compared with the 
sums of all the days after it in the period selected. By this means irregularities 
in the force upon any day have their effect on the final result to a considerable 
extent destroyed, as it is probable that the results will be as much too great in 
some cases, as they are too small in others. 
The whole differences have been summed without regard to days, and the 
signs of ¢,—¢,,, have been disregarded. 
The equation is, therefore, simply 
ZA(y) _ 
LA) 

TABLE V. 
Determinations of the Temperature Correction for the Balance Magnetometer, 
from comparisons of the Daily Observations at different periods. 













Time of 
PERIOD. ZA (t) ZA (y) q aa REMARKS. 
: 50° Fahr. 
1843. ° Mice. Div. Mic. Div. s 
Jan. 16—21. 525.3 4315.3 8.21 9.20 In 1843, there were 9 daily observations 
23—28. 817.7 5723.5 6.99 9.20 made at two-hourly intervals, from 
Jan. 30—Feb. 4. 576.0 4151.5 7.21 9.02 5 aM. till 9 P.M. 
Feb. 6—11. 609.9 4080.6 6.69 9.25 Sept. 2, the needle was remoyed, in or- 
June 1—30. 14320.4 |114646.9 8.006 9.28 der to determine its temperature cor- 
Sept. 6-—16. 1083.7 8730.4 8.04 9.92 rection by the method of deflections. 
1844. 
May 9—24. 8415.4 66621.7 7.93 8.38 In 1844, there were observations at 
Aug. 3—Sept. 6. 21696.9 | 171460.5 7.902 8.06 every hour of the day. 
For the series in The needle was removed between Sep- 
1843. \ BOS LSI ee 7.898 tember and February for temperature 
For all, 48045.3 | 379730.4 7.903 correction deflections. 

From the above table it would appear that neither the removal of the needle 
and readjustment, nor the alteration of the time of vibration, has affected the 
temperature correction. 
