PLO1 TING, among surveyors, is the art of .aping down on paper, &c. the se veral angles and lines of a tract of ground surveyed by a theodolite, &c. and a chain. In surveying with the plain table, the plotting is saved ; the several angles and distances being laid down on the spot, as fast as they are taken. See PLAIN. TABLE. But, in working with the theo dolite, semicircle, or circumferentor, the angles al e taken in degrees ; and the dis tances in chains and links, so that there remains an after-operation, tor educe these members into lines, and so to form a draught, plan, or map ; this operation is called plotting. Plotting, then, is per formed by means of two instruments, the protractor and plotting scale. By the first, the several angles observed in the field with a theodolite, or the like, and en tered down in degrees in the field book, are protracted on paper in their just quan tity. By the latter, the several distances measured with the chain, and entered down in the like manner in the field book, are laid down in their just proportion.— See SURVEYING.
PLOTTING-scale, a mathematical in strument, usually of wood, sometimes of brass, or other matter ; and either a foot or half a foot long. On one side of the in strument are seven several scales, or lines, divided into equal parts. The first divi Dion of the first scale is subdivided into ten equal parts, to which is prefixed the number 10, signifying that ten of these subdivisions make art inch ; or that the divisions of that scale are decimals of incites. The first division of the second scale is likewise subdivided into 10, to which is prefixed the nhmher 16, denot ing that sixteen of these subdivisions make an inch. The first division of the third scale is subdivided in like manner into 10, to which is prefixed the number to that of the fourth scale is prefixed the number 24; to that of the fifth, 32 ; that of the sixth, 40; that of the seventh, 48; denoting the number of subdivisions-equal to an inch, in each, respectively. The two last scales are broken off to make room fur two lines of chords. There is, also, on the back side of the instrument a diagonal scale.
As to the use of plotting, if we were required to lay down any distance upon paper, suppose 6 chains 50 links : draw an indefinite line ; then setting one foot of the compasses at figure 6 on the scale, e. gr. the scale of 20 in an inch, extend
the other to five of the subdivisions, for 50 links : this distance, being transferred to the line, will exhibit the 6 chains 50 links required.
If it be desired to have 6 chains 50 links take up more or less space, take them off from a greater or lesser scale, 1. e. from a scale that has more or fewer divi sions in an inch.
To find the chains and links contained in a right line, e. gr. that is just drawn, according to any scale, e. gr. that of 20 in an inch. Take the length of the line in the compasses, and applying it to the given scale, you will find it extend from the number 6 of the great divisions to 5 of the small ones : hence the given line contains 6 chains 50 links.
pLoTus, the darter, in natural history, a genus of birds of the order Anseres. Generic character : bill strait, pointed toothed; nostrils, a slit near the base ; face and chin without feathers ; legs short ; toes four, and all webbed. There are three species. P. anhinga, or the white bellied darter, is ache size of a mal lard, but measures nearly three feet in length. It is found in Brazil ; builds in trees and roosts in them at night, though living chiefly on fishes. In catching these its manner resembles that of ser pents. Drawing up its neck, it darts on its prey with its bill, and catches it in its claws. It is rarely seen on the ground, and, when not on the water in the pursuit of its food, it is to be seen on the most elevated trees, where it sits with its head drawn in between the shoulders. Its flesh is rank and oily. The black bellied anhinga is found in Ceylon and Java, and darting its long neck through the low shrubs immediately over the water, is, on the first view, mistaken frequently for some venomous reptile, and excites cor responding agitation and terror. The Surinam darter is of the size of a teal, and feeds on flies as well as fishes and water insects ; and in every att« mpt at destroying a fly by the dart of its bill it has been observed to succeed for a long continued time. It is often domesticated, and is called the sun-bird, from the cir cumstance, probably, of its often deve loping at once its tail and wing-s, and thus exhibiting a circular appearance of plumage, which, however, is certainly by no means glowing and ardent.