520 MR JOHN ALLAN BROUN ON THE HORIZONTAL FORCE 
the torsion circle in October 1843; the position of the mean for November 1843 
relatively to that for January of the same year, has been assumed with some 
reference to Hobarton and Makerstoun. 
16. The variations from August 1841 till February 1843 tieiserda generally 
the corresponding variations at all the other places:* from November 1843 till 
April 1844, the movement resembles that at Makerstoun; after April the force 
increases continuously till December 1844, wanting wholly the inflection towards 
August and September which is shown at Makerstoun and Hobarton (see Plate 
XXIII.); from December 1844 till April 1845, the variation resembles that at 
Makerstoun again; after which, as in the previous year, the force increases con- 
tinuously (with a slight inflexion, however, in July) till December 1845. 
17. This movement (1843-5) at Toronto is very remarkable. It is small from 
November till April in each of the two years, resembling that at Makerstoun; it 
is large in the remaining part of each year, not resembling at all the movement 
at Makerstoun. It is impossible to determine whether this difference is real; but 
it is very difficult to suppose that an accidental cause of movement should operate 
at exactly the same epochs in each of two years. I have not in my possession 
the observations for 1846, &c., of the bifilar magnet, though the monthly means 
of the bifilar are given in vol. ii. of the Toronto Observations. From these, after 
an approximate correction, I am induced to believe that the difference shown in 
1844, 1845 (April to December), between the Toronto and Makerstoun movements 
is not shown in the following years.} 
18. Care or Goop Horr.—tThe series was interrupted in April and November 
1848, again in October 1844, when a new magnet was employed. The movement 
resembles generally that at Makerstoun and Hobarton from October 1841 to 
October 1843, but with a less secular increase after May 1842; from November 
1843 till March 1844, the force diminishes continuously, differing wholly from the 
other two places; but from March till September 1844, the law of movement 
resembles that at Hobarton and Makerstoun. At this time (October 1844) a new 
magnet was substituted, and the force increased rapidly and continuously from 
* It should be noted that the monthly means depend upon hourly observations, excepting in the 
following cases, which depend on two-hourly observations :—Toronto, 1841 till July 1842 ; St Helena, 
1841 till September 1842; Trevandrum, 1841 till February 1842; Singapore, till June 1842; and 
in the case of Makerstoun, where the monthly means 1841—2 depend on 4 three-hourly observations ; 
18438, on 9 two-hourly observations; 1846, on 9 two-hourly observations; 1847, on 5 three-hourly 
observations; and 1848-9, on two observations daily. For this reason the means at the different 
places are not strictly comparable. 
+ I have corrected the Toronto Observations for 1846, 1847, and till June 1848, at which date 
the observations stop in vol. iil. (received since this paper was written). These are added in Table 
VIL., and have been projected (Plate XXIII); they show so considerable a resemblance to the obser- 
vations at Hobarton and Makerstoun as to render it probable that the different character of the move- 
ment in 1844—5-6 was due to instrumental causes, a supposition which is rendered more probable 
by the great difference between the temperature coefficient derived from the usual observations and 
from hot and cold water experiments. 

