and Directive Force of the Magnetic Needle. Al 
“At Hobarton there is one decided minimum throughout the 
year, and in the winter of the southern hemisphere but one max- 
imum. ‘The minimum is at 7 a.m. in the summer, and at 9 a.m. 
in the Winter. The winter maximum falls at 3 p.m. In the sum- 
mer there are two maxima, at noon and at 6 p.™., the latter max- 
imum being rather superior. Intermediate between these two af- 
ternoon maxima, is a small secondary minimum. e range of 
the diurnal variation is nearly the same at both periods of the 
year, and amounts to about four parts in a thousand of the whole 
Boe al 
tosphere, by reason of which the law of variation of the intensity 
of the system of primary ecliptic currents excited at a given hour 
by the sun is modified at particular localities, or what is more 
probable, the currents which have been developed subside more 
rapidly at some stations than at others. Thus we may explain 
the phenomena at Philadelphia by supposing that the residual cur- 
rents pass off very rapidly in the afternoon but are particularly effect- 
ive in the forenoon. The residual currents having passed off, the 
nocturnal currents come into sensible action, producing a second- 
ary maximum at 2 a.m; but at Toronto and Hobarton these cur- 
rents serve only to modify the diminution of the vertical force, re- 
salting” rom the slow subsidence of all the currents which are in 
Operation at sunset, ; 
IRREGULAR VARIATIONS. 
of 
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s. 
systems of currents. The following are among the more promi- 
nent indications of the irregular action of the radial and ecliptic 
currents. 
always have this effect; 2. The westerly variations of declina- 
tion have a maximum both in number and value, at Toronto, 
6 
