Book IV. 



IMPLEMENTS OF AGRICULTURE. 



375 



233 



SuBSECT. 2. Instruments of Science. 



2496. Scientific instruments are not much required in agriculture ; the principal are for 

 levelling, boring, and measuring. 



2497. The level is frequently required in agriculture, for arranging surfaces for irri- 

 gation, tracing strata in order to cut off springs, well-making, and a variety of other 

 purposes. The simplest form is the common road or mason's level, and the most com- 

 plete the spirit level, with a telescope and compass, such as is used by land-surveyors ; but 

 when operations of only moderate extent are to be performed, very convenient and 

 economical substitutes, and if used with care, equally accurate instruments, may be 

 found in Parker's level, the road or common level, water level, the triangular and the 

 square level. 



2498. Parker s level {fig. 233.) consists of two 

 cylindrical receivers of about five eighths of an 

 inch in interior diameter, and full three inches 

 high each, for holding quicksilver, fixed at right 

 angles upon a wooden stand, and about eighteen 

 inches asunder. A small groove is cut lengthwise 

 in the stand, and closely covered over, through which channel a communication is 

 effected between the two cylinders ; and consequently the surfaces of the quicksilver in 

 the cylinders must be on a level with each other. The two floats are equal to each other 

 as to weight and length, and the surfaces (about five eighths of an inch in diameter) 

 which rest on the quicksilver in each cylinder ; and consequently the tops of the floats 

 must also be on a level with each other. The different parts of the level are closely 

 fitted, and the whole rendered portable by screwing up the floats into the caps of their 

 respective cylinders. About three minute grooves are cut in the lower, or hemispherical 

 ends of the floats, through which the quicksilver rises upon a slight pressure of the floats, 

 and falls back again under the floats as soon as the pressure is taken off. The tops of the 

 cylinders are a little concave, for saving any particles of quicksilver which may lodge in 

 the screws, when the instrument has been shaken in the carriage. Constructed and sold 

 by Mr. Appleton of Drury Lane, London, turner: price 145. each; staff with cords and 

 pulleys, 8s., and three legs five feet high, 45. 



2499. The common level (Jig. 234.) is in general use among masons and bricklayers, 



234 



4= 



and for the purposes of road-making and irrigation it is furnished with plates of iron with 

 adjusting screws, for the purpose of determining the slopes of surfaces. 



2500. The water-level is that which shows the horizontal line by means of a surface of 

 water or other fluid ; founded on this principle, that water always places itself level or 

 horizontal. The most simple level of this kind is made of a long wooden trough or 

 canal, which being equally filled with water, its surface shows the line of level. It is also 

 made with two cups, fitted to the two ends of a straight tube, about an inch in diameter, 

 and three or four feet long, by means of which the water communicates from the one cup 

 to the other, and this pipe being movable on its stand by means of a ball and socket, 

 when the two cups shew equally full of water, their two surfaces mark the line of level. 

 It may also be made with two short cylinders of glass, three or four inches long, fastened 

 at each extremity of the pipe with wax or mastic. The pipe is filled with common or 

 coloured water, which shows itself through the cylinders, by means of which the line of 

 level is determined ; the height of the water with respect to the centre of the earth being 

 always the same in both cylinders. This level is very simple and commodious for level- 

 ling small distances. 



2501. The American or triangular level iJig.235. a) is formed of two pieces of thin wood joined by a cross bar, 

 the whole in the form oftiie letter A. The manner of using it is simply thus : At the place from which the 

 level is to be taken, drive a wooden peg into the ground, close in to the top, upon which one of the legs of the 

 frame or A may rest ; then bringing round the other leg till it touch the ground, there drive in a second peg, 

 turning round the other leg as before ; and where it touches the ground again, drive in another peg, and so 

 on along the whole line to be levelled. Thus, with very little trouble, and with as much accuracy as with the 

 finest spirit-level, may the course of a drain be easily ascertained. But as it is necessary that a drain 

 should have sufficient dechvity to allow the water to run freely, it will be requisite, in taking the level, 



B b 4 



