180 W. P. Riddell on Soletl’s Saccharimeter. 
by means of the compensator; and the direction in whieh the 
compensator has to be moved determines the quality of rotation; 
the distance over which it has to be moved determines the quan- 
tity or amount of that rotation. | 7 
, plate of left-handed quartz, equivalent in thickness to the 
two plates of the compensator, G, when set at zero ; and its ob- 
ject is to equilibrate the opposite effect of said compensator. 
, Compensator, composed of two wedge-shaped plates of 
right-handed quartz, the thickness of whose sum may be var 
by sliding their thicker or thinner extremities together ; at zero 
their thickness is equal to that of F’. If the principal part has to 
moved to the right, and the vernier to the left, the specimen 
under examination exerts a rotary influence to the right, and 1s 
consequently right-handed, and vice versa. The scale and vet- 
nier of this compensator is shown separately at 8. 
H, Analyzer, being a double refracting prism. 
J, Eye-piece, with two adjustable lenses, to fit the focus to 
different eyes. ‘The progress of a ray of common light (@) stt- 
king upon A, is as follows:—By A it is polarized, so as to vibrate 
in only one rectilinear plane, (6,) as the vibrations in all other 
planes are smothered. By B this polarized ray (b) is resolved 
into two sets of rectangular vibrations, (c,) one of which is retal- 
ded: by C these again are resolved into two systems of rectilin- 
ear, rectangular vibrations, (d and e,) one set of each system be- 
ing retarded, hence colored rays, one of which (e) only is received 
through D, By E the tint of this colored ray is changed, ¢ 
must be restored by G. The effect of F and G, being equiva 
lent, and mutually neutralizing, may be counted as nothing: } 
H the color of the rays is made visible, by bringing the VIDIe 
tions in a position so as to interfere in the same plane, awhich 1s 
necessary for the production of colored light. hic 
On the seale of the compensator, G, the figures 1 and 2 “ 
respond to quartz of an opposite polarization, whose thickness 18 
land 2 millimetres, and are read 100 and 200 degrees. TI 
smaller divisions are read 10 degrees each, while single degrees 
are read by means of the vernier. The degrees therefore corres 
pond nearly to $° in the deviation of the plane of polarization. 
Among substances which exercise an influerice on the pol 
zing apparatus, the most important, according to Pereira, ate 
par tes oils (those of mustard and bitter almond excepted). 
Aqueous solutions of several kinds of swgar, dextrine, tartare 
acid and tartrates (tartrate of alumina excepted). 
jabetic urine. 
Albuminous urine. 
Alcoholic solutions of camphor and artificial camphor. oh 
Most vegetable juices, shia 8 itt ue 
