We have here an arrangement that enables us to photograph the moon, stars, and planets. M. Faye has proposed that for the transit circle also the photographic method should be applied, the chronograph registering the time of the instantaneous opening of the slide, instead of the time the star is seen to transit, so that the position of the star with respect to the wires is registered at a certain known time; therefore, not only for physical astronomy have we the means of making observations without an observer at all, but also for position observations. Every one knows sufficient of photography to be aware that, if we wish to secure the image of a faint object, such as a faint star or a faint part of the moon, we must expose the plate for some little time, as we have to do in ordinary photography if the day is dull, and therefore the larger the aperture of the telescope the more light passes; and the shorter the focus is, and the more rapid the process, the shorter will be the exposure; if the focus is short, the image will be small; but as we can magnify the image afterwards, rapidity becomes of greater moment, as the shorter the time of exposure is the less atmospheric and other disturbances and errors in driving the telescope come into play. Still, if we photograph the moon or other object, we do not wish to limit ourselves to the size of the original negative obtained at the focus. If the negative is well defined—that is, if it possesses the quality of enlargeableness—there is no difficulty in getting enlarged prints. The method of enlarging photographs is very simple; all that is required is a large camera, the negative to be copied being placed nearer the lens than the prepared paper, so that the image is larger than the original. Fig. 209 shows an enlarging camera: the body, A, can be made of wood, or better still, of a soft material, bellows-fashion, so that the length can be altered at pleasure. In the end, at B, is fixed a lens—an ordinary portrait lens will do, but a proper copying lens is preferable; and E is a piece of wood with a hole in its centre, over which the negative is placed, the distance of E to B being also adjustible; then, by altering the lengths of B E and B C, the image of the negative can be made to appear of suitable size. At the end, C, a piece of sensitive paper is placed, and the light of the sun being allowed to fall through the negative and lens, the paper soon becomes printed, and can be toned and fixed as an ordinary paper positive. The camera may be carried on a rough equatorial mounting, consisting of an axis pointing to the pole, and pulled round with the sun by attaching a string to an equatorial telescope, moved by clockwork; or a heliostat can be used with more advantage, thereby allowing the camera to be stationary; a good enlarging lens is a very desirable thing, for most lenses seem to distort the image considerably. [Illustration: