13. A straight line drawn from any point in the axis of the cylinder, at right angles to the same, to meet the pano ramie surtiice, is called the distance of the picture.
1.1. The centre of a plane parallel to the axis, is the point where a straight line from the eye perpendicular to the plane meets it.
15. The panoramic centre of e plane parallel to the axis, is the point where a straight line drawn from the eye perpcn dicula• to the plane, cuts the picture.
10. The station point, is the point where the axis inter sects the original plane.
17. The centre of en original line, is the point where a straight line, drawn from the station point perpendicular to the original line, cuts the original line, 18. The panononic centre if an uriyinal line, is the point where a straight line, drawn fiom the station point purpen. dieular to the original line, cuts the picture.
19. The distance of an original plane parallel to the axis pout the picture, is the straight line drawn from the pano ramic centre to the centre of the original plane.
20. The distance of an original 'line front the picture, is the straight line drawn from the panoramic centre to the centre of the original line.
21. The distance of en original plane, is the straight line drawn fnon the eye to the centre of the original plane.
2..2, distance of on original line, is the straight line drawn from the station point to the centre of the line.
An original line parallel to the axis of the panorama has no vanishing points.
An original plane putallel to the axis of the panorama has two vanishing lines.
The vanishing line of a plane perpendicular to the axis of the panorama, is a circle on the panoramic picture; but if the panoramic surface be extended upon a Idalle, it becomes a straight line.
The vanishing lines of all planes inclined to the axis are ellipses, and when extended upon a plane become sinical curves, which are termed panoramic curves, as being the only kind of curve the cylindric picture produces when developed.
Pnotn.Em 1.—P/ute 1.—J'igure 1.—To describe the pano ramic curve to given dimensions.-1,et A 13 be the length of the curve ; bisect A 13 111 c, draw c n perpendicular to A a ; make c a, to the deflection of the :ire from the chord A 13 ; front the point c, with the distance c n, describe the quadrant u K; divide the arc n E into any number of equal parts, (say flow) also divide either half', c 13, into the same (1011• of equal parts ; let 1, i, y, be the points of in the quadrantal are ; draw 1 i q t. perpenill. cular to A u, cutting it at A', hi,/',' and let K, 11, It, he the points of division in c n ; druw K L, 11 1. F e, perpendicular to A a ; make K L, n 1, F c. respectiYely equal to A- 1, ; con struct perpendiculars upon c A, in the same manner; through all tire points 0, L, D, describe a curve, which will be that of t he panorama.
The curve A u B is that which would be found by cutting a semi-it\ tinder, whose eireurvfigcnye is A B. at an altitude, c D. distant on the surface from a plane perpendicular to the at a quadrant distance from the point A or 13 in the extremity of the diameter of the plane perpendicular to the axis. 'Isiterctitre the whole panoramic curve will be double the length of A is ; the other part being a similar and equal curve above the line A B, produced, and consequently a curve of enntrary flexure.
The panoramic curve takes place when the cylinder is cut by a plane at oblique angles to the axis.