IN THE MEAN EFFECTS OF THE LARGER MAGNETIC DISTURBANCES. 133 
For the purpose of making this examination, it appeared desirable to separate such 
a number of the larger disturbed observations occurring during the three years at 
Hobarton (commencing with the largest), as should bear nearly the same proportion 
to the body of the observations from which they were separated, as had been the case 
at Toronto. With this view it was necessary to approximate the line of separation at 
Hobarton more nearly to the mean or normal position of the magnet than at Toronto ; 
or in other words, to take a lower limit than at Toronto for the deflections of the de- 
clination magnet, either east or west of its mean position, which should be classed as 
belonging to the larger disturbances. The reason is twofold : first, the inclination at 
Hobarton is nearly 5° less than at Toronto (—70° 38' at Hobarton, and +75° 15' at 
Toronto), whilst the total magnetic force acting on the free needle is nearly the same 
at both stations ; an equal disturbing force will therefore produce a greater deflection 
of the declination magnet at Toronto, from mechanical considerations, than at Hobar- 
ton ; and second, that experience has fully shown that the disturbing causes them- 
selves act with greater energy, independently of the mechanical considerations re- 
ferred to, at Toronto than at Hobarton. It was soon found that a value taken at 
about two-thirds that at Toronto, viz. 3’4 scale divisions (or 2'*4 nearly in arc), would 
give nearly the same proportion of separated observations at Hobarton, as 5 scale 
divisions (or 3''6 in arc) at Toronto, and this value was accordingly taken. 
The number of observations thus separated was 1479; the system of observation 
being hourly, the total number of observations which should have been made in the 
three years (Sundays, Christmas days and Good Fridays excepted) is 22,392; the 
actual number was 21,436 ; the difference, 956, being occasioned partly by an inter- 
ruption of several days in June and July 1843, owing to the suspension-thread of the 
magnet breaking, and partly by observations being occasionally missed, as the hourly 
system was ratlier heavy for the establishment which had been left to carry it on. The 
proportion of separated observations is therefore 1479:21,436, or 1 : 14’5; the pro- 
portion at Toronto being 1 : 13’ 6. 
The 1479 disturbed observations are composed of 415 in 1843, 562 in 1844, and 
502 in 1845 ; showing, as at Toronto, 1843 to have been the least disturbed year of 
the three, and 1844 the most so. Taking the number in 1845 as unity, we have the 
numerical proportions as follows ; — 
Hobarton . 
1843 
0*83 
rl843 
0-84 
1844 
1-12 
Toronto . , 
• 
A 1844 
1-08 
1845 
1-00 
11845 
1-00 
This is quite as near an accordance in the proportion as it would be reasonable to 
expect, even on the extreme supposition of the disturbances being in all cases common 
to both stations, as, including the observations missed at Hobarton, between one-sixth 
apd one-seventh of the hourly observations at Toronto were without corresponding 
simultaneous observations at Hobarton : — 
