Level, an instrument by means of which a line may be drawn parallel to the horizon, in order to determine the height of one place with respect to another; for laying grounds even, conducting water, regulating descents, draining fens, etc.
There are various kinds of levels, adapted to different purposes, of which we shall notice only such as are of a simple construction, and in general use.
1. The Carpenters' and Paviors Level consists of a long ruler, in the centre of which is fixed, at right angles, another somewhat larger, and at the top of which is fastened a line, that shews the base to be horizontal.
2. The Masons'Level is composed of three rules, so joined as to form a rectangle, somewhat similar to the letter A; from the top of which a plummet is suspended, by means of a thread that passes over a perpendicular line marked in the middle of the base, if the object to which the level is applied be horizontal ; but which deviates from such mark, in case one side be lower than the other.
3. The Water Level, which shews the horizontal line by means of water or any other fluid, is founded on the principle that water is always level. The most simple instruments of this kind are made of a long wooden trough or canal, the sides of which are parallel to the base; so that, when it is equally filled with water, its surface points out the actual degree of declivity. Or, it may be made with two cups-fitted to each end of a pipe, three or four feet long, and about one inch in diameter, so that the water may communicate from one cup to the other : and, as this pipe is moveable on its stand, by means of a ball or socket, when the two cups become equally filled with water, their surfaces shew the line of level.—Instead of cups, however, two short glass cylinders, three or four inches in length, may be fixed to both extremes of the pipe, with wax or mastic. Some water, either plain or coloured, is now poured into the pipe, when the liquor appears through the cylinders, and thus the horizontal line is determined. This contrivance is very simple, and of great service for taking the level of small distances.
There are various other kinds of water levels, which have been designed with a view to ascertain declivities, for the purpose of irrigating land : as these, however, are either too complicated, or otherwise defective, we refer the reader to p. 31, of the present volume, where he will find an account of a more simple contrivance, illustrated with a cut, by Dr. Anderson ; and which is calculated to remove these difficulties.—Lastly, though we have several other instalments for taking levels in particular situations, yet, as their application requires a previous knowledge of mathematics, and is not strictly connected with domestic economy, our limits do not admit of farther descriptions.