176 W. P. Riddell on Soleil's Saccharimeter. 
tions centrally together, without changing their planes, we have, 
as before, one ray of unpolarized light, produced by vibrations in 
two rectangular planes. Thus we have a distinct idea of t 
difference between polarized and unpolarized light. 
There are several ways in which we may thus separate these 
two planes and hence produce polarization: viz, by simple reflec- 
tion at certain angles (differing for different substances); by single 
refraction, as by means of a bundle of thin glass plates ; by double 
refraction, as by means of acrystal of Iceland or cale spar; by 
transmitting a ray through a plate of tourmaline, which. has the 
pro of smothering or absorbing the vibrations in one direc- 
tion and permitting only those of the other plane to pass through. 
Circular polarization is a condition slightly different from 
the above, and is produced only when rectilinear vibrations are 
w 
water be half an undulation behind another of equal size, they 
mutually destroy each other; while the same, if of equal veloci- 
ties, may vibrate én vertical, right angled planes, with no sensible 
interference ; so may we conjecture in regard to these waves © 
dight-bearing ether. 
It may ‘be shown in various ways, that the result of the inter- 
ference of these rectilinear vibrations will be curvilinear vibra 
tions, a Movement which may be likened to “that of the ex 
tremity of ‘the swinging pendulum,” or more aptly to the spiral 
course of a coiled wire. If then we can retard the vibrations 2 
one érection, then briag them centrally in contact with those of 
the other direction, they mutually interfere, and no longer, 4 im 
the case of simply polarized light, produce common light; they 
‘ no longer vibrate in rectilinear planes, but in a curvilinear plane, 
the result of the two forces acting in the original reetilineat 
planes. By varying the amount of this retardation, we may PI” 
duce circular or even elhiplical waves. If this retardation amount 
to the one-fourth of an undulation, the waves will be circular, as 
can be shown by means of a very simple apparatus devised by 
Professor Wheatstone, + ahs 
It is found that crystal quartz possesses in a high degree 20 
power of retarding one of the two sets of vibrations; thus allo’ 
ing, In connection with hight properly polarized, cireular bat 
zation. * species of quartz exhibit what is termed TS 
handed polarization, kence called dextrogyrate ; some, left-h 2 
polarization, hence called levogyrate; the distinction betwe? 
which being as follows: its 
if we place a plate of Iceland spar, cut perpendicular 0 
principal or prismatic axis, in the polariscope, the polarizing © 
analyzing plates being crossed, we shall observe a gorgeous 
