and Directive Force of the Magnetic Needle. 27° 
At the summer solstice, we have, for the forenoon R+(e+z) 
=9'-69, for the afternoon, R— (e +2r)=3'80; whence R= 
6:74, and e+r=2'-94. The value found for R at the equi- 
noxes is 624, and of x, 0-92; hence to find ¢ at the summer 
solstice, we have the proportion 6°24: 6°74:: 0°92: 2= 0799, 
Thus e=2"94—2=1-95. If we make use of Table Il, we 
obtain R=7'-01, c=1"79, e=2'95—r=1' 16. At the winter 
solstice, in the forenoon, R+c—e=1" 15, in the afternoon R—z 
+e= whence “a 38, e—2#=0/ 23, To find z, 6724 
Attu; ¢=0° 21, -e=0’ Q342= 044. Table II gives R= 
2-56, 2=0''65, e=x—0’23=0/:42. It is to be observed that at 
the two solstices the ecliptic currents cross the meridian at right 
angles, at the hour of noon, and that therefore the values of e 
just determined show the effects of the ecliptic currents on the 
declination at 6 a.m. or at 6 p.m. At the equinoxes these cur- 
eR have but mane if any sensible effect on the declination at 6 
a.m. and 6 p. m., but cross the meridian obliqnely at noon, and 
rata the value of ¢ at the eqninoxes shows the effect of the 
a Ss currents on the declination at noon 
aving obtained these first approximations let us now proceed 
to a more minute investigation ;—taking into account the residual 
ecliptic as well as radial currents. 
Let R= deflection, in the semidiurnal interval, that would result 
from the variation in the intensity of the radial currents. 
i= effect, during same interval, of the variation of the ecliptic 
currents. 
r= effect at noon of the duets of the radial currents devel- 
oped during the foreno 
e= effect at noon of the reside of the ecliptic currents devel- 
oped during the forenoo 
7’= effect at 6 p.m. of the Tliao of the radial currents devel- 
NBs during thie afternoon. 
= effect at 6 p. m. of the residue of the ecliptic currents devel- 
aul during the afternoon. 
mr= portion of residual radial currents at noon that pass off 
in the afternoon. 
ne= portion ey peopel ecliptic currents at noon that pass off 
n the afterno 
ee (nearly) ; py (nearly). 
At the E'quinoves; in the forenoon, we have (from = 0; : 
Aut. Eq., R+r+E—e=8"65; Ver. Eq., R+r— 
Hence E=1’-49, R—7 ‘I6te=r. r>e, whence R<7':16. Fa the 
afternoon the equations are, Aut. Eq., R+E+mr—r’—ne—e¢ = 
7°89; Ver. Eq.. R—E+mr—r —ne—e=2"'78. From which we 
pies B=2'55, R=5'33—(mr—r'—ne—e)=5'33+-r(1—m)+ 
e(1+2), (nearly). No account has been taken of the residual 
