. Mathematics, compiled from the best authors and intended to be the text-book of the course of private lectures on these sciences in the University at Cambridge [microform]. boundary parallel to the substile, intersecting theline from the centre of the dividing circle in d. Then, byProb. XVI. of Geometry, find a fourth proportional to if, fa,and dc ; and set it from c to h. A line, drawn from thecentre of the dial through the point h, as aV in this exam-ple, will be the hour line required. Note 2. The stile may be a triangular plate similar toAED, placed perpendicular to the plane of the dial
. Mathematics, compiled from the best authors and intended to be the text-book of the course of private lectures on these sciences in the University at Cambridge [microform]. boundary parallel to the substile, intersecting theline from the centre of the dividing circle in d. Then, byProb. XVI. of Geometry, find a fourth proportional to if, fa,and dc ; and set it from c to h. A line, drawn from thecentre of the dial through the point h, as aV in this exam-ple, will be the hour line required. Note 2. The stile may be a triangular plate similar toAED, placed perpendicular to the plane of the dial on thesubstile ABba ; and the edge AD will show the stile may be lengthened or shortened by producing orcurtailing the side AD. Or the gnomon may be a perpen-dicular pin on E, and in height equal to ED ; and then theshadow of the top will point out the time. Note 3. When this dial is used, its plane must be hor-izontal, and the XII oclock line on a meridian line, withthe end B toward the north. Note 4. This dial shows all the hours of the artificialday at any season of the year. 352 MATHEMATICS. PROBLEM VII. To draw geometrically an erect direct south diaL. ITU \ \ \.UlJLA_\1 iirrir v i\i - 1. Take a convenient point A, and through A draw themeridian,or XII oclock line, AB ; and at the distance Aa,equal to the thickness of the stile, draw ab parallel to AB. 2. Make the angle BAD equal to the compliment ofthe latitude of the place. Assume a point E in the lineAD, and draw EF perpendicular to AB. Draw EG per-pendicular to AD, and through G draw the contingent lineHI perpendicular to AB, representing the equinoctial. 3. Make GK, gk, each equal to GE, and with any rad-ius, as GK, and K, k, as centres, describe the quadrartta CL, gl, and divide each into six equal parts. Through the DIALING. 353 points of division draw lines from the centres K, k, cuttingHI in the hour points m, m ; n, n, &c. Then lines, drawnfrom the centres A, a, through the points m, m ; n, n, &
Size: 1721px × 1452px
Photo credit: © Reading Room 2020 / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1800, bookidmathematicsc, bookyear1808
