120 



THE POPULAR EDUCATOR 



was insisted on in those days, this objection of the opposing 

 parties was held to be fatal, and Sir David lost his patent. 



When a small object is placed as described, an harmonious 

 circular figure, consisting of eight sections, is apparent ; alto- 

 gether, the Magic Designer is not to be despised, and some 

 Very pretty effects aro produced by placing fern leaves, flowers, 

 bits of colourad worsted, paintings, mosaic drawings, on a sheet 

 of paper, and then placing the instrument upon them ; thereby, 

 as the "affiche" to the toy states, not only affording infinite 

 amusement to everybody, but being also of great value, as the 

 patterns may be copied at leisure. 



Continuing the optical amusements, it may be stated 

 that the Encyclopedic Me'thodique, of 1792, thus describes the 

 method of drawing a distorted figure on a plane surface, which, 

 when observed from a certain point, recovers its former shape 

 and true proportions : Having drawn correctly on a sheet of 

 paper the figure proposed to be designed, enclose it in a square, 



4he triangle E G H, and by drawing those parts of the outline 

 contained in the different squares of A B c D in the expanded 

 form in the corresponding trapeziums or perspective squares, the 

 portrait becomes distorted. It is, however, soon restored to the 

 right appearance if viewed through a hole K (Fig. 3), so hollowed 

 out in the piece of wood L that the hole looked through is the 

 apex of a cone, the base of which is directed towards the distorted 

 drawing. The piece of wood L is placed upright at the point H, 

 and its height must not exceed the distance between H and i. 



Hutton states that there was in the Convent of the Minimes, 

 in the Place Eoyale, Paris, the distorted picture of a Magdalen 

 at prayers, which could be restored to a perfect and beautiful 

 work of art if looked at in the manner already described. 



The Encyclopedic Methodique of Montucla, though presenting- 

 many ingenious optical illusions, is not quite to be relied on in 

 the philosophic explanation given of some of the effects, though, 

 Hutton, in his translation of this work, accepts fVifltn, Thus, 



as at A B c D (Fig. 3), and divide the latter into several other 

 small squares, by dividing the sides, say into seven equal parts, 

 and then drawing straight lines through the corresponding points 

 of division, just as the engravers do when they intend to make a 

 reduced drawing from a picture ; mark out on a board a paral- 

 lelogram, E B F Q, and divide one of the two shorter sides, as E G, 

 into as many equal parts as D c (one of the sides of the square 

 A BCD), and therefore into seven equal portions. From the 

 centre of the other side of the parallelogram B F, marked H, 

 draw straight lines to the points of division of the opposite 

 side E G, the outside lines of which will be H E, H G. Having 

 then assumed at pleasure, in the side B F, the point I, above 

 the point H, as the height of the eye above the plane of the 

 picture, draw from I to the point E the straight line E I, which 

 will cut those lines coming from the point H in the points 1, 2, 

 3, 4, 5, 6, 7. Through these intersecting points draw straight 

 lines parallel to each other, and to the base E G of the triangle 

 E G H, which will thus be divided into as many trapeziums (plain 

 figures contained, as Hutton says, under four right lines, of 

 which both the opposite pairs are not parallel) as there are little 

 equares in the square A B c p. 

 By transferring the portrait contained in the square ABCD to 



"faire qu'un objet vu distinctement, et sans 1'interposition 

 d'aucun corps opaque ou diaphane, paroisse renverse a 1'ceil nu ;" 

 i.e., in plain English, "to make an object, which can be seen dis- 

 tinctly without the interposition of any opaque or semi-trans- 

 parent body, appear to be inverted :" Cut a slip of card-board 

 (Fig. 4) three inches wide and twelve inches long, and bend up 

 the two ends, A B and c D, so that they each take up three 

 inches, leaving six inches in the centre. In the middle of the 

 end A B make a round hole, about a line and a-half in diameter, 

 and in the centre of it fix a pin, or the point of a needle, as 

 shown at E (Fig. 4). Exactly opposite to it in the other end c D, 

 make a hole F with a large pin. If the eye is now applied to E, 

 whilst turning the hole F towards the flame of a candle, or other 

 bright source of light, the head of the pin now appears to be in- 

 creased in size, and in an inverted position, as represented at G. 

 Montucla says, and Hutton tacitly approves by repeating it, that 

 " the reason of this inversion is, that the head of the pin being 

 exceeding near the pupil of the eye, the rays which proceed from 

 the point F are greatly diverged on account of the hole F ; and 

 instead" of a distinct and inverted image, there is painted at 

 the bottom of the eye a kind of shadow, in an upright position. 

 But inverted images on the retina convey the idea of upright 



