28 W. A. Norton on the Variations of the Declination a 
action at 6 a. m. of the nocturual currents, but this must be very 
slight, especially as the effect. of the ecliptic currents is reduced 
to zero at that hour. Since this action must be the same at one 
Its only effect will be to increase slightly the value of R. f 
the determination of 7, we have the equations R= 5’-33+r(1—m) 
1’'83—ne 
nae -- (1), R+r=7'16+e...(2); whence r=—>—— 
t the Summer Solstice ; for the forenoon, R+E+r—e=9" 
4), Shi the afternoon, R-E+ mr—r—ne—e=3''80 . Me 
Whence E=2"-94— ren Leoene ..(6), R=6"744+—— ot 
(7). To take account of residual action of the nocturnal ct 
reuts, at 6 let z denote the effect of the residual radial ¢ 
rents at thet tig and y that of the residual ecliptic currents: 
and y will each te 
therefore, supposing these currents to pass off entirely during t 
forenoon, instead of ory (4) we have R+E+r—e+r+y 
9-69... (8), and instead of (6) Ety=2'04 eet 
oh Be 
(9); also R=6-744——, + Or At the | 
ter Solstice, R-E+r—e= ‘: iss: tix R+E+mr—r—ne 
1-62...(12); and'thus B=0934 mine (18), a 
R=1- yenee el .(14). If we take account of 
residual nocturnal currents in action at 6 a.m, E+y=0/23+ 
= lect Bes me. (15), R= 1384 es aa 
If we a Pee eqs. (6) and (13), accenting the letters 
cee ae 
Since E and E’ represent the effects of the ecliptic currents 
on the declination at the hour of 6 a. m. at the summer and wi 
ter solstice, respectively, this formula should give the deflec- 
tion of the ‘needle at that honr, due to the ecliptic currents 
the interval between the solstices. T'o take account of the resid- 
ual nocturnal currents we must introduce into the formula the 
as r+z2’ 
2 
eq. (13), we obtain S=E+E/=3"-17— 
terms * The exact value of this expression cannot 
readily be found, but we know that it must be a very small 
quantity. In the calculations which follow it is neglected. 
