Defcription, Nature, and General Use

OF THE

SECTOR

AND

PLAIN-SCALE

Briefly and Painly laid down.

ÁS ALSO

A Short ACCOUNT

·

OF THE

USE S

OF THE

Lines of Numbers, Artificial Sines,
and Tangents.

Stous, k

-The FOURTH EDITION.

LONDON:

Printed for THO. WRIGHT, Mathematical Inftrument
Maker to His MAJESTY, at the Orrery, near
Water-Lane, in Fleet-Street, 1746.

ADVERTISEMENT.

TH

HE great Encouragement Mr. WRIGHT has had for above feventeen Years paft, in making large ORRERYS, with the Motions of all the PLANETS and SATELLITES, and the true Motion of Saturn's Ring, has made him fo ready and perfect, that Gentlemen may depend on having them made reasonable and found, not liable to be out of Order:

As may be seen by one he made for Mr. Watts's Academy in Tower-Street.

Another for His MAJESTY at Kenfington. Another for the New Royal Academy at Portf mouth.

Another for his Grace the Duke of Argyle, (late Lord Ila.)

And feveral other large ones for Noblemen and Gentlemen.

He has also great Choice of Mathematical Inftruments ready made; as Cafes in Silver, Brass or Ivory, Surveying Inftruments, Sun-Dials, Weather-Glaffes, Reflecting-Telescopes of dif ferent Lengths, &c.

Sothern Hist. of 11-22-28 18513

THE

PREFACE.

OMETHING concerning the DeScription and Use of the Sector and Plain-Scale being at this time very much wanted, and fo I prefume will be very acceptable, therefore I have compiled this fmall Treatife of them; in which is briefly contained, their Defcription, Nature, and General Ufe.

S

In the first Chapter is contained, not only the Defcription of the Lines upon the Plain-Scale, but likewife their Construction and Nature are therein bewn: As also a fhort Account of their Ufe. In the fecond Chapter is contained, the Defeription of the Sector, and the Lines now commonly placed thereon.

In the third Chapter is fhewn, the Ground and General Ufe of the Sector. From this Chapter it appears, that the Sector ferves as a Scale to all Radius's, not greater than its Length, when A 2

quite