Extract from Stereometry; or the Art of GAUGING made easie, by the Help of a Sliding-Rule by Tho. Everard (1727) pp 42-43

Sect. III.

The use of the Rule in mesuring of Superficies; and first, of a Circle.

The Area or Superficial Content of a Circle is found by the Diameter or Circumference; I shall therefore first shew how by either of these to find the other.

Problem. I.

The Diameter, or Circumference of a Circle, either being given, to find the other.

The Circumference of that Circle whose Diameter is Unity (or 1) is* 3.1415926536 but for our purpose 3.141592 will suffice: Therefore, as 1 is to 3.14159, so is the Diameter of any Circle to the Circumference: By the Instrument thus:

     Set 1 on the Line A, against 3.141592 on the Line B, then against any Diameter on the Line A, you have the Circumference on the Line B; and the contrary, thus: Against

  { 20 }   { 62.851 }
 These Dia-  { 30 }  you have these  { 94.247 }
meters { 40 }  Circumferences,  { 125.663 }
  { 50 }   { 157.079 }

Or, Contrariwise, against

  { 20 }   { 6.366 }
 These Circum-  { 30 }  you have these  { 9.549 }
ferences { 40 }  Diameters,  { 12.732 }
  { 50 }   { 15.915 }

And so of any other.

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This page was last updated on 29 March 2000.