TO DRAW A PLOT of this field, ACCORDING TO THE PRE

CEDING RULES.

Having drawn the side AB, according to the directions before given for laying off the first course and distance, compare the first and second courses together, and they will be found to be both north and both east; consequently, the angle between them is found by RULE 4, as follows: 16° 30′ the less course, and 98° the supplement of the greater being added, the sum is 114° 30', for the angle at B. Compare the second and third courses, and they will be found to be one north and one south, and both east; consequently, according to RULE 2, 82° the second course added to 17° the third course, the sum 99° is the angle at C. The third and fourth courses are both south, and one east and the other west. The angle between them at D is 126°; for 17o the third course added to 37° the fourth course is 54°, which subtracted from 180° leaves 126o, according to RULE 3. The fourth and fifth courses are one south and the other north, and both west. According to RULE 2, 37° the fourth course added to 49° the fifth course, the sum 86° is the angle at E.

A little practice will render this mode of protracting a field familiar and easy, and an attention to the courses will show in what direction the angle is to be made.

The above field may be protracted, and its area calculated according to the directions given in the preceding EXAMPLES.

SEVERAL FIELD BOOKS TO EXERCISE THE LEARNER IN PLOTTING FIELDS AND CALCULATING THEIR AREA.

TO SURVEY A FIELD FROM ONE STATION AT ANY PLACE WITHIN THE FIELD, FROM WHICH THE SEVERAL ANGLES MAY BE SEEN.

Take the bearing of the angles, and measure their distance from the station.

Draw a meridian line as N S.

From some point in that

line as a centre, lay off the bearing and distance to the sev eral angles, and draw lines from one angle to another, as

TO FIND THE AREA.

The Area may be calculated according to PROB. XII. by measuring diagonals and perpendiculars; or more accurately according to PROB. IX. RULE 4.

As the bearing and distance of the lines from the station to the several angles are known, two sides and their contained angle are given in each of the triangles into which the plot is divided; the area may, therefore, be readily calculated by the RULE above referred to.

NOTE. As in the operation, the logarithm of radius is to be subtracted from the sum of the other logarithms, it may be done by rejecting the left hand figure, without the trouble of putting down the ciphers and subtracting.