INTRODUCTION AND RESULTS. 
247 
Lefroy, having occasion to return to England in the spring of 1846, brought with 
him from Toronto to Woolwich for that purpose. The particulars are contained in 
the subjoined Table ; the ratio resulting from them is identical with that obtained 
by the absolute method, viz. T835 to T372. 
Table V— Observations with Fox’s Circle to determine the relative Intensity of the 
Magnetic Force between Toronto and Woolwich. Needle C. 5 '= * 000 1 7. 
Station. 
1846. 
Angles of deflection. 
Thermometer. 
Intensity. 
Woolwich = 1-372. 
1*5 gr. 
2-0 grs. 
2-5 grs. 
3-0 grs. 
Toronto . . 
Woolwich. . | 
March 28. 
March 31. 
April 2. 
May 26. 
May 28. 
19 59-2 
20 02-8 
19 59-5 
27 03-2 
27 14-5 
27 44-7 
27 37-7 
27 39-6 
38 34-6 
38 33-8 
33° 19-7 
35 11-0 
35 13-5 
50 41*7 
50 53-2 
44 18*5 
44 13-5 
44 18-0 
69 42'5 
69 30-3 
42-6 
57-3 
69*0 
}68-4 { 
1 1-835 
j 1-372 
We have therefore three determinations of the total Force at Toronto expressed 
in the arbitrary scale, which are as follows : — 
By the statical method in 1842 T838 
By the absolute method in 1845-46 .... T835 
By the statical method in 1846 C835 
I have therefore concluded on taking T836 as the value in the arbitrary scale of 
the total Force at Toronto ; and as all the relative determinations discussed in this 
memoir were either originally made in reference to Toronto as a base station, or 
have become connected with it by subsequent comparison, they form one series, and 
the values expressed in this scale, in the general table, No. XLVIII., are all depen- 
dent on T836 as the Force at Toronto ; and will all require to be increased or di- 
minished should future investigations show that T836 has been incorrectly adopted. 
Having then the values of the total Force at Toronto, T836 in the arbitrary scale, 
and 13-896 in absolute measure, arbitrary values are convertible into absolute by 
the factor — — — r , and absolute into arbitrary by - The absolute values of the 
total Force in the general table, No. XLVIII., have been thus computed in all cases 
when the original determination was a ratio, either total or horizontal ; when the 
original determination was of the absolute horizontal Force, the absolute total Force 
computed therefrom is the product of the horizontal component and the secant of 
the observed Inclination. 
The simplest form, in which an approximate representation of the isodynamic ovals 
round the point of maximum, and within a limited distance of it, may be computed 
2 k 2 
