When the camera is made for the express purpose of taking Kaleidoscope pictures, it becomes a very simple instrument and may be constructed easily and cheaply. It requires no lens excepting the small one =L L= of rock crystal or of glass, a quarter of an inch in diameter. The aperture required for this lens is so small that the spherical and chromatic aberration cannot injure, in any sensible manner, the distinctness of the picture. The difference between the chemical and luminous focus, which cannot be made to coincide with a single lens, may be easily determined by experiment, or in order to avoid this, the small lens may be made achromatic.[16] [16] A thin lens of rock crystal will transmit more of the actinic rays than one rendered achromatic. The form of the camera as fitted up with one of Mr. Bate’s Kaleidoscopes, with metallic reflectors, is shown in the annexed figure, where =M C D N= is the body of the camera, _m n o p_ the tube which is moved out and in by a milled head attached to the pinion which drives the rack on the tube _m n o p_. The Kaleidoscope =A B L L=, exhibiting the figure which is to be copied, is temporarily fixed in this tube by pieces of cork or wood, so that its axis, or the line of junction of the reflectors, may be perpendicular to the surface of the grey glass _p q_, which can be taken out, so as to allow the collodion or paper slide to be placed in the same groove. [Illustration: FIG. 53.] The pictures should always be taken, when it is possible, by sunlight incident obliquely upon the object-box, or with the illuminators already described. When this cannot be done, artificial light, containing the actinic or chemical rays, may be thrown upon the object, as shown in Fig. 52. The light of coal gas, which may be condensed for any length of time upon the objects in the object-box, will be found to answer the purpose; but if a more rapid process is required, we may, as proposed by Mr. Moule, use the Bengal lights, which contain a large quantity of the actinic rays.[17] These lights are composed of _six_ parts of _nitre_, _two_ of _sulphur_, and _one_ of _the sulphuret of antimony_. The powder is made up in the shape of a cone, which is ignited at the top; but it would be better to spread it out widely, in order that it may be condensed upon the object-box. The lime-ball light may also be employed, but the Bude light, which is a coal gas flame, rendered more intensely luminous by a stream of oxygen, is preferable to any other artificial flame. In using it, or any other of the lights already mentioned, for obtaining Kaleidoscope figures, it must either be placed very near the object-box, or condensed upon it by a large lens, on account of the small size of the aperture at the eye-end of the Kaleidoscope. [17] See the _Journal of the Photographic Society_, vol. iv. p. 137.