Perspective and geometrical drawing adapted to the use of candidates for second and third-class teachers' certificates . om the eye. From long practice we are enabled to tell the height of ahill, breadth of a river, or capacity of a ship, though at a con-siderable distance. If we hold a rule of definite length closeto the eye, and then withdraw it six or eight feet away, wenotice that it is apparently smaller. Experience teaches usthat it is not really smaller, the apparent diminution beingonly the effect of distance. Perspective aims, then, at measuring and representingobjects as they appear
Perspective and geometrical drawing adapted to the use of candidates for second and third-class teachers' certificates . om the eye. From long practice we are enabled to tell the height of ahill, breadth of a river, or capacity of a ship, though at a con-siderable distance. If we hold a rule of definite length closeto the eye, and then withdraw it six or eight feet away, wenotice that it is apparently smaller. Experience teaches usthat it is not really smaller, the apparent diminution beingonly the effect of distance. Perspective aims, then, at measuring and representingobjects as they appear at a distance. The horizon always hounds our vision. If we look out upon a large lake we find that the sky andwater appear to meet; this line of apparent union is called 10 DRAWING. the horizon. No matter how large an object is, if it recedesfar enough from us on a lake, it would at length appearon the horizon as a point. If a person stands on a level plain he can see over a rangeof 60 degrees in every direction without moving his point on the horizon directly in front of him is calledthe Centre of Now, if we take this point as a centre, and join it with theeye of the observer, and draw lines at an angle of 30° with itfrom the observers eye, we shall form a hollow cone, whichrepresents his range of vision : thus, if the observers eye beat the point X, and AB represent the horizon, and 0 thepoint on it directly in front of X, if CX be joined, andAX, BX be drawn at an angle of 30 degrees with CX, AB INTEODUCTION. 11 will be the horizontal range of the spectators vision. If wedescribe a circle from centre C, and distance CA or CB, suchcircle will be called the base of the cone of visual rays; for itwill be observed that from point X the spectator can see justas far as the edge of this circle. The ground as a plane isgenerally supposed to extend to the horizon, and is markedfor sake of abbreviation, G. P. The horizontal line is un-limited in length, and is writte
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Keywords: ., bookcentury1800, booksubjectgeometricald, booksubjectperspective
