14 THE ROYAL SOCIETY OF CANADA 
were (1) an ordinary electric are and (b) a Leyden jar discharge between 
cadmium terminals. The former gives a very bright continuous 
visible spectrum and the latter is rich in ultraviolet giving a decided 
continuous background, while the cadmium lines serve for reference 
marks. 
The light was polarised and anlaysed by means of fluorite plates 
placed parallel to one another and so arranged that the light was 
incident on each at the polarising angle tan—' A, (A=1-43). Fluorite 
was used on account of its transparency to the ultraviolet, and also on 
account of the fact that there is but little variation in its index over a 
large range of wave lengths. The light was received by a spectrograph 
and the spectrum photographed with this arrangement of apparatus, 
the blackened parts of the negative or the white part of the 
positive correspond to wave lengths for which the rotation had been an 
integral number of times 180°. 
Figure I shows two, photographs of the spectrum made in this way, 
the one made by a quartz spectroscopic system and the other by a 
Uviol glass system; and the values for the rotations for a series of wave- 
lengths are shown in the following Table:— 
No. of A Rotation No. of À Rotation 
band. x 107 mm. | per mm. band. x 107 mm.| per mm. 
Le, at 7252... |. + 14:03° PR ES VAE 2850 112-21° 
Deere 6460 | 18-70 VE AERAT ER ae A 2800 116-88 
ren aay 5670 23-38 Baek: POSE 2755 121-56 
As ee eee 5190 28-05 LS ME 2715 126-23 
iE ieah ee tet 4860 32-73 Die ene oes 2675 130-91 
Gas IN 4595 -| 37-40 DIE Sis A 2635 135-78 
(igus Miter? 4355 | 42-08 DREAM 2 2600 140-26 
Beets he ae 4155 46-75 ZA als gee hs 2565 144-93 
AO SAIT TOR 3980 51-43 BOT ee Gs 2535 149-61 
Oe ee ee 3830 56-10 ger ee ae 2505 154-28 
AGS At es 3700 60-78 EE aha tier 2480 158 -96 
MOS AISAE See 3590 65-45 SB ETES 2455 163 - 64 
Ue iar Mee 3480 70-13 ST eee ee 2430 168-31 
Te ie miami 3380 74-81 Do eaten 2405 172-99 
DOME EN 3290 79-48 BG PRE 2380 177-66 
chee ge RE 3210 84-16 das nuk tuipiavs 2355 182-34 
IY ip Cane 3140 88-83 ee ES 2330 187-01 
Ke PAPER CE CSA 3070 93-51 DO Ae 2310 191-69 
| a ee eae 3010 98-18 AD ER 2290 196-37 
AU ea aa a 2950 102-86 cn nae eae 2270 201-04 
7 | TS à 2900 107-53 
Various formulæ have been proposed to express the rotatory dis- 
persion of optically active substances. Two types in which the numbers 
refer to a quartz plate of thickness one millimeter are as follows:— 
