Identifier: encbritannica11macf (find matches)
Title: Encyclopædia britannica : or, A dictionary of arts, sciences, and miscellaneous literature : constructed on a plan, by which the different sciences and arts are digested into the form of distinct treatises or systems ..
Year: 1797 (1790s)
Authors: MacFarquhar, Colin, ca. 1745-1793 Gleig, George, 1753-1840
Subjects: Encyclopedias and dictionaries
Publisher: Edinburgh : Printed for A. Bell and C. MacFarquhar
Contributing Library: University of California Libraries
Digitizing Sponsor: Internet Archive

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e through whichit Is obferved. The dlftances are reckoned from theobjtct-glafs of the telefcope; and the anfwers obtainedbv the rules of this problem, though not exaclly true^are however fo little diirerent from the truth, that thediilerence feldom anioirnts to more than two or tUreeinches, which may be fafely neglcfted. Rule 1. If the angle-be exprciTed in minute--,fay, as the given angle is to 60, fo is (87.^5 to afourth proportional, which gives the aulwcr in inches.— 2. If the angle be exprefltd in feconds, fay, althe given angle is to 360:, fo is 687. jj to a fourthproportional, which exprcffes the anfwer in inches.—3. If the angle be exprcfled in minutes and fcico-.ids, turir it all into feconds, and proceed as a-bove. Example. At what diftance is a globe of onefoot in diameter when it fubtends an angle ot twofeconds ? 2 : 3600 : : 687,55 3600X687.55 _ = i23590 inches, or 10? 1324 feet, which is the anfwer required.I This M 1 (Mi () M F. TER ^7^, riatP CCXCAl. y ^^ -.y^^./^.
Text Appearing After Image:
-r-r-V-r-f-T-f-ri« * ,; /r If /J? A -/ ^« / * * ? * * ^^ ^y. /fr//,AfH //.rA /.^*^.A,/.W/r I Mia c 79; *f Thfs palculatipn nifty be (1;er;$;qp4 ( fof fipce twoof the three proportionals are fixed, thpip produft if?the f)rft cafe is 41253, an4 in the othgr twp csfeg t^4475! So ; f^ •^t ^^ i^ csfe, viz. wher) thg angleis fxpieflcd in minutes, yoj) need only djvida 41^53t)y the given angle t aqd in the other twQ caffs, viz,when the angle is exprefTed jn fecondg, divide f±-j^ioqty the given angle, and thg quotient in either pafe mthe anf\ver in inches. Problem 11. The angle, not exceedfjig one de,gree, which is fiibtcnded by any known ei^tenfion,teing given, to find its diftance frpn) the placg of oh-,fervation, Rule, Proceedasif the eKtenfion were of one footfjy Problem J, and call tha anf\7er B ; then, if theextenfion in queftion be esjprefled in inches, fay, as 12inches are to that CKtenfion, fo is B to a fourth pro-portional, which is the anfwer in inches j but if theextenfion in

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