# The Description, Nature and General Use, of the Sector and Plain-scale: Briefly and Painly [sic] Laid Down. As Also a Short Account of the Uses of the Lines of Numbers, Artificial Sines and Tangents

T. Wright, 1746 - Mathematical instruments - 44 pages
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Page 4 - The circumference of every circle is supposed to be divided into 360 equal parts, called degrees ; and each degree into 60 equal parts, called minutes ; and each minute into 60 equal parts, called seconds ; and these into thirds, etc.
Page 2 - A chord (BD) is a right line drawn from one end of an arc to another, and is the measure of the arc. The chord of an arc of 60 degrees is equal in length to the radius of the circle of which the arc is a part. 17. The segment of a circle is a part of a circle cut off by a chord.
Page 3 - The SECANT of an arc is a right line drawn from the centre through one end of the arc to meet the tangent drawn from the other end ; thus CT is the secant of the arc AS.
Page 2 - The sine, or, as it is sometimes called, the right sine, of an arc, is a right line drawn from one...
Page 3 - K and PHQ are tangents. A tangent of a circle is at right angles to the diameter drawn through the point of contact. There may be tangents to other curve-lines as well as to circles.
Page 10 - Joint like a Carpenter's Rule ; fo that the faid Legs, together with certain right Lines, drawn from the Center of the jokit, contain Angles of different Quantities.
Page 9 - Miles make a Degree ; in the Latitude of 60 Degrees, 30 Miles make a Degree ; in the Latitude of 80 Degrees, 10 Miles make a Degree.
Page 9 - The graduated line of chords is necessary, in order to show the latitudes ; the line of longitude shows the quantity of a degree on each parallel in sixtieth parts of an equatorial degree, that is, miles. The lines of tangents, semitangents and secants serve to find the centres and poles of projected circles in the stereographical projection of the sphere. The line of sines is principally used for the orthographic projection of the sphere. The lines of latitudes and hours are used conjointly, and...
Page 9 - Latitude : As, in the Latitude of no Degrees, that is, under the Equator, 60 Miles make a Degree ; in . the Latitude of 40 Degrees...