ATMOSPHERIC MAGNETISM — DIURNAL VARIATION— DIRECTION. 
61 
as they were for Hobarton ; and I may refer to the words then used, substituting- 
Fig. 13. 
Toronto for Hobarton, and north for south (2901.). As the sun comes up from the 
east in his course between the two places, he drives, by the altered atmosphere 
beneath him, the upper ends of their needles before him, and outwards from the line 
of his path, as if he were a north pole to the Hobarton magnet, and a south pole to 
the Toronto magnet. By 22 o’clock, the earth’s force, and the action of the air due to 
the sun’s position, permit a return to the east, though the inclination for a time in- 
creases (2902.) ; both swing rapidly round from west to east as he passes over the 
meridian, and then having attained their maximum position eastward, soon follow 
after him under the influence of the earth’s force, less and less counteracted by the 
retreating sun. So striking is the similarity between Hobarton and Toronto, that 
Colonel Sabine has already especially distinguished and described it*, and has shown, 
that, laying down the direction of motion in both cases by curves, and bringing the 
two curves together by their faces, they coincide almost exactly, with this single dif- 
ference, that the Hobarton changes precede those at Toronto by an hour, or rather 
more, of local time. 
2910. We cannot represent this day effect experimentally upon two such needles as 
those at Hobarton and Toronto by one pole of a magnet, though we can do it with 
each separately with different poles : but we see at once from the hypothesis, the 
reason why the sun acts in this manner (2877-), and how it is that the region of 
influential atmosphere that accompanies him in his journey round the globe, acts 
with one effect in the northern latitude and another in southern positions (2903.). 
The reasons also for the short time of the day journey and the lengthened period of 
the night return (2904.), are manifest. The occurrence of disturbances or secondary 
waves of power in the night time, and the condition both of the chief variation and 
the subordinate oscillations in summer and winter, will be considered hereafter. 
2911. Greenwich . — The following results are taken from the volume of Greenwich 
Observations for 1847- The latitude is 51° 31' N., and being removed nearly 80° in 
longitude from Toronto, the station is well contrasted with it and also with Hobarton. 
* Hobarton Magnetical Observations, 1850, p. xxxv. 
