AND ITS TEMPERATURE CORRECTION. 



77 



The first values of q shew that periods of a week are insiifiadent for very 

 accurate determinations. 



The mean for 1843 is almost identical with that for 1844. 



19. The differences for three periods were also summed without regard to 

 days, but paying attention to the sign of t-t,„. The following table contains 

 the results. 



Table VI. 



Determination of the Temperature Correction for the Balance Magnetometer, 



reo-ard being paid to the signs of the differences of temperature. 



The result No. 16, and the mean results in Tables V. and VI., for the whole 

 periods, agree very closely. As the value of one micrometer division, in parts of 

 the whole^ertical force, is about 0.00013, the greatest difference of the three 

 final results, 7.83, 7.90, and 7.81, is 0.0000012. 



The final results, from five days' observations, by the method of deflections, 

 were .000085, .000077, .000079, .000062, .000073, differing 0.000023. 



The results, from the comparison of daily observations, in parts of the whole 

 vertical force, will be about .000134, the time of vibration being about 9 seconds; 

 if 11 seconds were adopted, the result would be .000095 ; in either case consider- 

 ably more than the result obtained by deflections. 



20. The satisfactory determination of q for the Balance magnetometer, led me 

 to determine the correction for the Bifilar magnetometer by the same method. 



Besides the variation of the magnetic moment, temperature also affects 

 the length and interval of the suspending silver wkes ; it probably also affects 



their elasticity. 



The determination of the correction from the daily observations, at once sums 

 up aU the effects of temperature. When the suspending threads are of silk, these 

 sources of error are avoided; but I conceive that much gi-aver errors are intro- 

 duced, due chiefly to varying humidity affecting the torsion of the thread. 



I shall give simply the results of the comparisons of the daily observations for 

 the Bifilar magnetometer. 



VOL. XVI. PART I. ^ 



