RULER, PARALLEL.. In its usual form, this instrument consists of two rectangular rulers connected by two cross-bars of equal lengths, which move on pivots in the rulers in such manner that the four pivots, two in each ruler, shall be the four points of a parallelogram. One ruler being held. fixed, and a line drawn with the edge of the other ruler in any position, then any motion given to the other ruler by the rotation of the cross bars gives, on the edge of the moving ruler, a line parallel to the first line. To give the instrument more extent, three rulers are sometimes put together, each connected with the next by cross-bars in such manner that the cross-bars connecting the first and second have an opposite revolution to those connect-' ing the second and third.
The rolling parallel ruler consists of an ordinary ruler of rectangular form, both edges of which are bevelled and divided into inches and tenths, or otherwise. Two short rollers of equal diameters, and connected by an axis of nearly the same length as the ruler, are let into perforations made in the latter, so that when the instrument is moved perpendicularly to its length on the paper, lines drawn along either of its bevelled sides are to one another. • Perpendiculars to a given line are drawn • by adjusting the ruler so that any division on a bevelled edge may travel on the given line.
RUM. This well known spirit is distilled from cane-juice, or the soummings of the juice from the sugar-boiling-house, or from treacle, or molasses, or from dander, the lees of former distillations. As the entire juice of the cane is not necessary for making rum, the distillation is carried on in conjunction with the manufacture of sugar. The best rum is made from the uncrystallised syrup called molasses. [Moussus.J The proportion of molasses made in crystallising a cwt. of sugar varies from 50 to 00 gallons, and depends both upon the climate and the season, being lowest in the Leeward Islands, which have a dry climate, and highest in Demerara and Trinidad, and it is in the latter that in fine seasons the proportion reaches 00 gallons per cwt. Nearly one gallon of proof rum may be made from one gallon of molasses. The best rum is from Jamaica ; the worst from the Leeward Islands. Tho consumption of rum in England is diminishing; its place being filled by gin and British brandy. In the finer qualities of Jamaica rum, slices of pine apple are put into the hogsheads ; and the liquor then obtains the name of pine apple ruin.
A few statistics relating to Rum will be found under Salm TRADE.