resultant vibrations in Polarized Light. 379 
(7.) The same, the axis inclined 45° to the left, and the atoms 
revolving from right to left. 
8 
tricity Ae vary to any degree, from the straight line on the one 
e circumference of a circle on the other. 
It is unnecessary to state what is the relation of the cams of 
the two axes, for presenting a 
these varieties of polarization; to 
escribe one or two is sufficient. 
Let a cam of the lower axis, Fig. 
3, be at its highest position, and 
3. 
night, about to commence its mo- 
tion to the left, as it descends; 
then the ball both descends by the 
first cam, and moves to the kt b 
second, at equal rates; and there- 
fore oscillates in a plane, which 
i) 
cams is at the highest point, the corresponding. upper one shall 
be also at the highest point; then, when the ball descends by the 
left, till a semi-cireumference is completed, and so on. This is 
right-hand circular polarization (4), provided the vibrations are 
propagated from particle to particle toward the observer. These 
and the other cases can be exhibited by the instrument in less 
lime than is required to describe them. 
{n one particular this instrument is inferior to Plucker’s. In 
ug, the balls in their com ponent motions, strictly describe straight 
Ines, in & vertical or a horizontal planes But in this, these mo- 
lecular motions, as exhibited by the balls, are obviously arcs of 
circles ; consequently, all the compound motions deviate from 
the lines which have been mentioned. As the radius, however, 
18 18 inches, and the are only about two inches, the curvature is 
hot easily noticed. Since the whole purpose of the instrument 
18 to produce motions which visibly agree with those determined 
by theory, in order to illustrate the subject to the mind of the 
pupil, the failure to fulfil the exact theoretical conditions is un- 
important, while the mechanical advantages of this mode of 
Producing the vibrations are obvious. 
‘A Mass, Oct, 4, 1861. 
