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a brass tube, containing the regulator with its nicol near the 

 opening and the quartz plate behind it. The rotation of the 

 tube is effected by the wheel and pinion worked by the rod and 

 milled head. 



The ocular part of the instrument contains, next to the 

 trough, the quartz plate of the compensator, and next to this 

 on the other side from the trough, two quartz wedges. Each 

 wedge is cemented to a similar wedge of glass so as to form two 

 piano-parallel plates, which are set in brass frames. One of 

 these plates is fixed while the other has a horizontal sliding 

 motion for which purpose it is provided at the bottom with a 

 side to side rack and pinion motion worked by the milled head 

 underneath. The frame on the upper edge of the movable plate 

 carries the divided scale and that of the fixed plate a vernier. 

 For reading the latter an inclined mirror throws the image of 

 the scale along the axis of the small tube above, fitted with an 

 eye piece. 



The remainder of the ocular part contains the analyser and 

 telescopic lenses, the eye-glass being movable. 



The small screw-head, projecting to the right of this part, 

 admits of the analyser being adjusted to its proper position in 

 relation to the fixed polariser. It is only used in the original 

 adjustment or re-adjustment of the instrument, i.e., when we 

 cannot by any movement of the quartz wedges bring a uniform 

 tint into the two halves of the field. To re-adjust, both wedges 

 together with the fixed plate are removed, and the screw turned 

 until a uniform tint prevails. To fix the zero another screw is 

 attached to the quartz wedge frame carrying the scale, and allows 

 a certain amount of adjustment of the latter. The length of the 

 solution tube must be accurately known. 



In using the polarimeter, it is set up at least two inches from 

 a gas or paraffin lamp with a metal chimney having a side 

 opening. 



A tube empty or filled with water is laid in the instrument, 

 and the eye-piece of the telescope drawn out until the 

 joining line bisecting the circular bi-quartz appears sharply 

 defined, the movable quartz wedge is then adjusted by the 

 milled head underreath, until both halves of the field have a 

 uniform tint. The regulator is then moved by the milled head 

 fixed on the long horizontal rod so as to bring into view that 

 sensitive tint, which, with the slightest displacement of the 

 movable quartz wedge, produces the most distinct colour 

 differentiation in the two semi-circles. For most eyes the best 

 tint is the nearest approach to white. 



Having decided upon the sensitive tint the quartz wedge is 

 adjusted to give the greatest similarity in colour in the two 

 halves, and the reading on the scale noted. This should be 

 repeated several times, the mean being taken as the zero of the 

 instrument. If the zero of the scale does not coincide with this 



