The instrument constructed by Mr. Ruthven is also a Universal Kaleidoscope, which unites the properties of a Polyangular one with those of Annular and Parallel Kaleidoscopes. Its construction will be understood from Figs. 42, 43, and 44, where =A B E F G H= represents a frame of iron or brass, which slips into the tube. The two sides =A B=, =F H=, of this frame, are kept together by _four_ cross pieces, _a b_, _c d_, etc., the other two corresponding to these being invisible in the figure. The two reflectors, the ends of which are seen at =Aʹ O=, =Bʹ O=, are each fixed to a plate of metal _p p_, a section of which is seen in Fig. 44. Each plate of metal has four cylindrical pins, _p_, _p_, etc., both on its upper and under edge. The two pins nearest the ends of the reflectors pass through openings in the cross pieces _a b_, _c d_. On the top of the frame is placed a plate of brass =M N Q P=, in which are cut grooves _e f_, _g h_, _k l_, _m n_; _e f_ and _k l_, and also _g h_ and _m n_, being parallel to each other. This plate can be moved forwards and backwards between the cross pieces _a b_, _c d_, by means of a small screw =S S=, working in a female screw fixed upon the edge =N O= of the plate, and as the middle pins _p p_, attached to the plates which carry the reflectors, pass through the grooves, any change in the position of the plate =M Q=, produces a change in the distance, _p p_, of the pins, and consequently in the distance of the upper edges of the reflectors. By turning the screw =S S=, therefore, the upper edges of the reflectors may be either brought into contact, or separated to a distance regulated by the inclination of the grooves _e f g h_. A similar plate with a similar screw is placed upon the lower edges of the reflectors, so that we are furnished with the means of giving the plates any inclination to each other, or placing them at any distance within certain limits. For example, if the lower edges of the plates are in contact, we can vary the angle of their inclination by separating or closing their upper edges by means of the upper screw. By separating the lower edges, we give them the position for annular patterns, and by making the distance of the lower and upper edges the same, we obtain from them rectilineal patterns; and the figures of these annular and rectilineal patterns may be either contracted or expanded, by altering the distance of the plates when in this parallel position. [Illustration: FIG. 44.] CHAPTER XIII. ON THE CONSTRUCTION AND USE OF POLYCENTRAL KALEIDOSCOPES.