Transactions . straight-edge, at the 6 feet mark, to bring the pointof the pencil into line with the true side, and to help keep it inplace. By carrying the bevelled end of the straight-edge around, and incontact with the walls of the furnace, and keeping the true sidealways against the needle, a curve was traced on the paper whichgave the exact distance from the centre of the furnace to any pointof the wall in the plane of section; for it is evident that if we drawany line passing through the centre, C, 3 (Fig. 9) for instance, thedistance from the centre to the circumference on that line is
Transactions . straight-edge, at the 6 feet mark, to bring the pointof the pencil into line with the true side, and to help keep it inplace. By carrying the bevelled end of the straight-edge around, and incontact with the walls of the furnace, and keeping the true sidealways against the needle, a curve was traced on the paper whichgave the exact distance from the centre of the furnace to any pointof the wall in the plane of section; for it is evident that if we drawany line passing through the centre, C, 3 (Fig. 9) for instance, thedistance from the centre to the circumference on that line is equal tothe fixed distance on the straight-edge, plus the portion of the lineincluded between the centre and the curve on the measurementsheet. To make the drawing, lines are drawn by means of a protractorthrough the centre of the measurement-sheet (by preference makingequal angles with one another), 0, 1, 2, 3, 4, 5, 6, 7, Fig. 9, andthe distances cut off on them from the centre to the curve are meas- FiG. Fig. 10. iwo/i/r ( ? ^yA * // \ XV\ \J/ ^^^^ BM IK ured and written down on them. Having selected the scale, draw acircle whose radius to scale is the fixed distance on the rod—in thiscase 6 feet (Fig. 10), and draw radii with the protractor correspond-ing to those drawn on the measurement-sheet. We have now onlyto lay off, to scale, on each radius (in Fig. 10) from the circumfer-ence of the circle, the distances previously found for it and writtenon the measurement-sheet, and to draw a line through the pointsthus found. It is important to have points, such as E (Figs. 9 and10), at which the distance from the centre is a maximum or minimum,fixed with precision. To do this, draw a circle on the measurement- 108 HYDRO-GEOLOGY. sheet with the same radius as the circle Fig. 10; draw a radiusthrough the point to be found, and measure the distance cut off onit by the measurement-curve. This radius is easily laid off on , by taking the distance from its intersection wit
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Keywords: ., bo, bookcentury1800, bookdecade1870, booksubjectmineralindustries
