# The description, nature and general use, of the sector and plain-scale: briefly and plainly laid down. As also a short account of the uses of the lines of numbers, artificial sines and tangents

Printed for Tho. Wright; and sold by Tho. Heath mathematical instrument maker, next the Fountain Tavern in the Strand., 1721 - 44 pàgines

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### Continguts

 Secció 1 1 Secció 2 14
 Secció 3 44

### Passatges populars

Pàgina 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.
Pàgina 2 - The sine of an arc is a straight line drawn from one end of that arc, perpendicular to a diameter passing through the other end of the same arc. Thus FG is the sine of the arc BF, or it is the sine of the supplemental arc FAH¿>. The sine of an arc of 90° is equal to the radius, for AC is the sine of the, arc BA. The sine of an arc of 30° is equal to half the...
Pàgina 9 - Infpe&ion, how many Miles there are in a Degree of Longitude, in each feveral Latitude: As, in the Latitude of no Degrees, that is, under the Equator, 60 Miles make a Degree ; in the Latitude of 40 Degrees...
Pàgina 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...
Pàgina 5 - AB; from eveiy of which Degrees let fall Perpendiculars on the Semidiameter EB, which Perpendiculars will divide EB into a Line of Sines, to which you muft fet the Numbers io, 20, &c.
Pàgina 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.
Pàgina 5 - Quadrant AB, and they will divide the Semidiameter AE into a Line of Semitangents : But becaufe the Semitangents on Scales run to 160 Pegreesj continue out the Line AE, and draw L'". .: Lines fcihcs from the Point C, thro...
Pàgina 8 - And contrarywife, to meafure the Quantity of an Angle already laid down. The firft is done by...
Pàgina 6 - Arcs cutting the Chord AC, which will divide AC into a Line of whole Rhumbs ; and after the ^arne.
Pàgina 32 - As the Sine of the Angle BAG is to the Sine of the Side BC, fo is the Sine of the Angle BCA to the Sine of the Side AB fought.