Next comes the question of testing the quality of the objective. (The stand is meanwhile assumed, but will be spoken of later.) Point the telescope to a star of about the third magnitude, and employ the eye-piece of highest power, if more than one goes with the instrument--this will be the shortest eye-piece of the set. If the glass be of high quality, the image of the star will be a neat round disc of small size, surrounded by one or two thin bright rings (Fig. 8, _a_). Should the image be elliptical and the rings be thrown to the one side (Fig. 8, _b_), the glass may still be quite a good one, but is out of square, and should be readjusted by an optician. Should the image be irregular and the rings broken, the glass is of inferior quality, though it may still be serviceable enough for many purposes. Next throw the image of the star out of focus by racking the eye-piece in towards the objective, and then repeat the process by racking it again out of focus away from the objective. The image will, in either case, expand into a number of rings of light, and these rings should be truly circular, and should present precisely the same appearance at equal distances within and without the focus. A further conception of the objective's quality may be gained by observing whether the image of a star or the detail of the moon or of the planets comes sharply to a focus when the milled head for focussing is turned. Should it be possible to rack the eye-tube in or out for any distance without disturbing the distinctness of the picture to any extent, then the glass is defective. A good objective will admit of no such range, but will come sharply up to focus, and as sharply away from it, with any motion of the focussing screw. A good glass will also show the details of a planet like Saturn, such as are within its reach, that is, with clearness of definition, while an inferior one will soften all the outlines, and impart a general haziness to them. The observer may now proceed to test the colour correction of his objective. No achromatic, its name notwithstanding, ever gives an absolutely colourless image; all that can be expected is that the colour aberration should have been so far eliminated as not to be unpleasant. In a good instrument a fringe of violet or blue will be seen around any bright object, such as Venus, on a dark sky; a poor glass will show red or yellow. It is well to make sure, however, should bad colour be seen, that the eye-piece is not causing it; and, therefore, more than one eye-piece should be tried before an opinion is formed. Probably more colour will be seen at first than was expected, more particularly with an object so brilliant as Venus. But the observer need not worry overmuch about this. He will find that the eye gets so accustomed to it as almost to forget that it is there, so that something of a shock may be experienced when a casual star-gazing friend, on looking at some