Fig. 55.
Fig. 56.
We come now to consider the claims of Mr. Bradley, Professor of Botany in the University of Cambridge. In a work, entitled, New Improvements in Planting and Gardening, published in 1717, this author has drawn and described Kircher’s apparatus as an invention of his own; and, instead of having in any respect improved it, he has actually deteriorated it, in so far as he has made the breadth of the mirrors greater than their height. An exact copy of the mirrors used by Bradley is shown in [Fig. 55], from which it will be at once seen, that it is precisely the same as Kircher’s, shown in [Fig. 54]. We are far from saying that Bradley stole the invention from Kircher, or that Kircher stole it from Baptista Porta, or that Baptista Porta stole it from the ancients. There is reason, on the contrary, to think that the apparatus had been entirely forgotten, in the long intervals which elapsed between these different authors, and there can be no doubt that each of them added some little improvement to the instrument of their predecessors. Baptista Porta saw the superiority of two mirrors, as a multiplying machine, to a greater number used by the ancients. Kircher showed the relation between the number of images and the inclination of the mirrors; and Bradley, though he rather injured the apparatus, yet he had the merit of noticing, that figures upon paper, which had a certain degree of irregularity, like those in [Fig. 56], could still form a regular figure.
In order that the reader may fully understand Bradley’s method of using the mirrors, we shall give it in his own words:—
“We must choose two pieces of looking-glass (says he), of equal bigness, of the figure of a long square, five inches in length, and four in breadth; they must be covered on the back with paper or silk, to prevent rubbing off the silver, which would else be too apt to crack off by frequent use. This covering for the back of the glasses must be so put on, that nothing of it may appear about the edges on the bright side.
“The glasses being thus prepared, they must be laid face to face, and hinged together, so that they may be made to open and shut at pleasure, like the leaves of a book; and now the glasses being thus fitted for our purpose, I shall proceed to explain the use of them.
“Draw a large circle upon paper; divide it into three, four, five, six, seven, or eight equal parts; which being done, we may draw in every one of the divisions a figure, at our pleasure, either for garden-plats or fortifications; as, for example, in [Fig. 55], we see a circle divided into six parts, and upon the division marked F is drawn part of a design for a garden. Now, to see that design entire, which is yet confused, we must place our glasses upon the paper, and open them to the sixth part of the circle, i.e., one of them must stand upon the line b, to the centre, and the other must be opened exactly to the point c; so shall we discover an entire garden-plot in a circular form (if we look into the glasses), divided into six parts, with as many walks leading to the centre, where we shall find a basin of an hexagonal figure.
“The line A, where the glasses join, stands immediately over the centre of the circle, the glass B stands upon the line drawn from the centre to the point C, and the glass D stands upon the line leading from the centre to the point E: the glasses being thus placed, cannot fail to produce the complete figure we look for; and so whatever equal part of a circle you mark out, let the line A stand always upon the centre, and open your glasses to the division you have made with your compasses. If, instead of a circle, you would have the figure of a hexagon, draw a straight line with a pen from the point c to the point b, and, by placing the glasses as before, you will have the figure desired.