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GEODÆSIA Improved.

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CHAP. I.

Containing the DoBrine of plane Triangles.

T Rigonometry is that Part or Branch of the Mathematicswhich treats particularly about Triangles: It consists ofLines and Angles only, wherein having three Things given, viz.three Sides, two Sides and an Angle; and two Angles and aSide, a fourth may be obtained or found ; so that in a compa-rative Sense, it is not much unlike the Golden Rule, for theMiddle Number must be of the fame Name with the Thingsought or required.

In the geometrical Part of this Treatise, Chapter the 2d, thereare some Definitions relating to Trigonometry, but as they arenot sufficient for a Learner, whereby he may have a clear andthorough Knowledge thereof, it is therefore necessary to intro-duce the following

Definitions.

i. A Triangle is comprehended under three Lines, and con-sisteth of six Parts, viz. three Lines or Sides, and three Angles.

2. A plane Triangle is projected on a plane Superficies,and con-sequently its Sides are Right-lines. See Def 6, Page 71.

3. When two Sides crossing each other make the Angles onall Sides equal, then those Angles are Right-angles, and theLines are perpendicular.

4. A Degree is the 360th Part of the Periphery, or Circum-ference of a Circle, equal to 69 English Miles, and somethingbetter than an rfalf.

5. The Complement of any Number of Degrees, is what theywant of 90.

6. A