Tempeeature Coefficient of the Balance Magnet. 



xlvii 



number of days compared are too few to give good results.* It is obvious, however, 

 that if we consider the equation 



?' = 



2 A y,. r a 



2 A L 



AL 



that the value of q' deduced from the quantity 



2 Ay^ 



2 A L 



alone will be too much or too 



little according as the sign of a tr is positive or negative ; whence, if a period of 

 moderate length be selected, throughout which the mean daily temperature increases 

 and diminishes considerably, we may neglect the sign of a t^ and the quantity a, as 

 in the summations the coefficients of the latter will nearly destroy each other. For 

 periods of moderate length, and free from disturbances, it is the fact, as may be 

 seen from the previous Table (with the exception of one day), that the signs of a y^ 

 and A t^ are always opposite. The latter method, then, will be found the easiest, 

 and, it is conceived, in general the most accurate. The mean results obtained for 

 the series, June — ^July, when t^ ^ and <^ t^^^, are indeed exactly the same, and 

 the partial results seem to indicate that the sign of a is itself so variable as to render 

 its total effect nugatory. The same remark applies to the series August — Septem- 

 ber 1844. 



The following Table contains a series of results obtained according to the latter 

 method. In each series each day is compared with every day following it to the 

 end of the series for the differences a y and a t : — 



Table 16. — Determinations of the Temperature Coefficient for the Balance Magnet 

 from Comparisons of the Daily Observations. 











Observed 





Period. 



2a(0 



2A(y) 



?' 



Time of 

 Vibration. 



Kemarks. 



1843. 



o 



Mic. Div. 



Mic. Div. 



B. 





Jan. 16 — Jan. 21 



525-3 



4315-3 



8-21 



9-7 



In 1843 there were 9 daily obser- 



Jan. 23— Jan. 28 

 Jan. 30 — Feb. 4 



817-7 

 576-0 



5723-5 

 4151-5 



6-99 

 7-21 



9-7 

 9-5 



vations, made at two-hourly in- 

 tervals, from 181^ till lOt. 

 Sept. 2, the needle was removed in 

 order to determine its tempera- 



Feb. 6— Feb. 11 



609-9 



4080-6 



6-69 



9-4 



June 1 — June 30 



14320-4 



114646-9 



8006 



9-7 



ture correction by the method of 



Sept. 6— Sept. 16 



1083-7 



8730-4 



8-04 



10-8 



deflections. 



1844. 













May 9 — May 24 



8415-4 



66621-7 



7-93 



8-6 



In 1844 there were observations 



Aug. 3— Sept. 6 

 For the series in) 



21696-9 



171460-5 



7-902 



8-5 



made at every hour of the day. 

 The needle was removed between 



17933-0 



141648-2 



7-898 



9-8 



September 1843 and February 



1843, ... J 











1844 for temperature experi- 



For all, . . . 



48045-3 



379730-4 



7-903 



8-5 



ments. 



The mean value of q' from the series in 1843 is 7-90, and from the tempera- 



* Such as these results are, however, their disagreement with the result obtained by deflection ex- 

 periments and vibration, is, in each case, even more than that of the adopted result. 



