i i i 
and Directive Force of the Magnetic Needle. 29 
The determination of the deflection produced by the ecliptic 
currents, in the interval between the solstices, from formula (17) 
admits of verification. We have seen (p. 201), that, for the 
hour of 6 a.m., the entire deflection in this interval is the sum 
of the effects of the ecliptic and radial currents, and that for the 
hour of 6 p. m. the deflection during the same interval is the dif- 
ference of the eflects of these two systems of currents. Now let 
E= effect of the ecliptic currents at 6 a.m. or 6p. m.; R= effect 
of radial currents at the same hours ; e and r the effects of the 
residual ecliptic and radial currents, respectively, at 6 a.m.; and 
e’, r’, the effects of the two systems of residual currents which 
are in action at6 p.m. Then, (by Table I,) E+ R+e+r=4"-90, 
e’—e r+r 
E—R-+é+r’=1'-46 ; whence, E+e=3"18-5-- a . (18), 
Tt will be seen, when we come to discuss the variations of the 
_ horizontal force, that the intensity of the ecliptic currents is 
twice as great, at the hour of noon, at the winter as at the sum- 
mer solstice; but on the other hand these currents pass off, from 
the vicinity of the zenith, about 44 p.m. It is probable, there- 
fore, that the effect of the residual ecliptic currents at 6 Pp. m. is 
nearly the same at the two solstices, and accordingly that e’, 
which is the difference between the individual effects at oe sol- 
ger 5 
_ stices, is a “small quantity in comparison with 7”. 3 mpd‘ g are 
a8 ere r 
also small quantities. If we neglect 3 and 5 we have D= 
E+e=3" 48-5 (nearly)... (19). This formula should give 
nearly the same value for the deflection as formula (17 
The following Table contains the results given by the formule 
which have just mee investigated, corresponding to certain as- 
sumed values of ma 
rer Summer — — Betstives | 
R é 8 al 
m=1,n=1 ileal as eh Pa a5 rai 0 i033 area '97 ‘65 
m=0, n=0 Verret 2 -02/0 -92/0 15,1 -53/0 0-15)2 45 2 82 
m=4,n= baile gale erlt jolatels 2110 4810-2510 1812 53 2 
m=3,n= = “41/6 5612-10) 1 -22/0 -20/ 1 -5510 -47/0 -27)0- le: 58 2 
The process of it a is as follows: It was first a, 
that at the equinoxes the wy effects of the residual radial - 
r into equ. (3), we obtain the value of e, and thence the value of 
R has nearly the same value at the summer solstice as at the 
