The light from a gas burner enters at the extremity of the instrument and first passes through the “regulator A,” which consists of the double refracting Nicol’s prism _a_ and the quartz plate _b_, it being so arranged that it can be turned round its own plane, thus varying the tint of the light used, so as to best neutralise that possessed by the sugar solution to be examined. The incident ray now penetrates the polarising Nicol’s prism B, and next meets a double quartz plate C (3·75 millimetres in thickness). This quartz plate, a front view of which is also shown in the figure, is divided in the field of vision, one half consisting of quartz rotating to the right hand, the other half of the variety which rotates to the left hand. It is made of the thickness referred to owing to the fact that it then imparts a very sensitive tint (purple) to polarised light, and one that passes very suddenly into red or blue when the rotation of the ray is changed. Since the plate C is composed of halves which exert opposite rotary powers, these will assume different colours upon altering the rotation of the ray. After leaving the double quartz plate the light, which, owing to its passage through the Nicol’s prism B is now polarised, enters the tube D containing the solution of cane sugar under examination; this causes it to undergo a right-handed rotation. It next meets the “compensator” E, consisting of a quartz plate _c_, which has a right-handed rotary power, and the two quartz prisms _d_, both of which are cut in a wedge shape and exert a left-handed rotation. They are so arranged that one is movable and can be made to slide along the other, which is fixed, thus causing an increase or decrease in their combined thickness and rotary effect. The ray of light then passes through the analysing Nicol’s prism F, and is finally examined by means of the telescope G, with the objective _e_ and ocular _f_. Fig. 3 gives a perspective view of the Ventzke-Scheibler polariscope. The Nicol’s prism and quartz plate which constitute the “regulator” are situated at A and B, and can be rotated by means of a pinion connecting with the button L. The polarising Nicol’s prism is placed at C, and the double quartz plate at D. The receptacle _h_ contains the tube P filled with sugar solution, and is provided with the hinged cover _h´_, which serves to keep out the external light while an observation is being taken. The right-handed quartz plate and the wedge-shaped quartz prisms (corresponding to _c_ and _d_, Fig. 2) are situated at G, and at E and F, and the analysing Nicol’s prism is placed at H. When the wedge-shaped prisms have an equal thickness coinciding with that of the quartz plate _c_ (Fig. 2) the left-handed rotary power of the former is exactly neutralised by the right-handed rotary power of the latter, and the field of vision seen at I is uniform in colour, the opposing rotary powers of the two halves of the double quartz plates C (Fig. 2) being also equalised.