ON A CHARCIED ELECTPJC CONDENSER MOVING THROUGH SPACE. 
1G9 
fZE 
the couple tending to increase xjj is — which is 
N (-Y sin 2xp - 
\ V 
1 -f- ( - j cos^ ijj 
clN 
dxjj 
If we assume N independent of xff, the couple is N sin 2xfj. 
2 
V 
dN .T 
If N changes so that couple is always zero, = N [ —j sin 2ifj {neglecting small 
\ V 
quantities of 4th order). Suppose « is the velocity of the earth’s way through 
space, represented by OD (fig. 3). Let plane of con¬ 
denser be yZ, and OZ the axis of suspension. Let plane 
ZOD cut plane xy in OH ; let X be the ZOD and fx the 
angle yOH. 
Now component of velocity along axis of suspension 
cannot rotate condenser about OZ, so that effective 
component is u sin X, and the expression for the couple 
1 becomes 
N {sin® X sin 2y,. 
A’ 
The experiment can be so arranged that X = 90° and y = 45°, and the couple 
reduces to N 
N 
Tlte best Conditions for Experiment. 
The following considerations show clearly the best conditions for making the exper 
ment, in respect to time of day, time of year, 
and azimuth of the plane of the condeii.ser. 
(i.) The variation of the direction of drift 
with time of year. 
Consider the celestial sphere (fig. 4). Let 
2 be the position of the sun on the ecliptic 
Tt. If Q be a point such that SQ = 
then OQ will be the direction of the drift past 
the earth. 
Let SNQ = 
Let QY = y, the declination of the point Q. 
If w = obliquity of the ecliptic, 
« = right ascension of the sun. 
Tan tQ cos 26 ’ = tan tY 
tan tQ = — cot tS, since SQ = 
= — cos ?c/tan a, 
Fig. 4. 
VOL. ecu. — A. 
Z 
