the end of its tube and examined. Should the examination lead to the detection of bubbles or even scratches in the glass (quite likely the latter if the instrument be second-hand), these need not unduly vex its owner's soul. They do not necessarily mean bad performance, and the amount of light which they obstruct is very small, unless the case be an extreme one. But on no account should the two lenses of the object-glass itself be separated, for this will only result in making a good objective bad and a bad one worse. The lenses were presumably placed in their proper adjustment to one another by an optician before being sent out; and should their performance be so unsatisfactory as to suggest that this adjustment has been disturbed, it is to an optician that they should be returned for inspection. The glass may, of course, be carefully and gently cleaned, using either soft chamois leather, or preferably an old silk handkerchief, studiously kept from dust; but the cleaning should never amount to more than a gentle sweeping away of any dust which may have gathered on the surface. Rubbing is not to be thought of, and the man whose telescope has been so neglected that its object-glass needs rubbing should turn to some other and less reprehensible form of mischief. For cleaning the small lenses of the eye-pieces, the same silk may be employed; Webb recommends a piece of blotting-paper, rolled to a point and aided by breathing, for the edges which are awkward to get at. Care must, of course, be taken to replace these lenses in their original positions, and the easiest way to ensure this is to take out only one at a time. In replacing them, see that the finger does not touch the surface of the glass, or the cleaning will be all to do over again. [Illustration: FIG. 8. _a_, O.G. in perfect adjustment; _b_, O.G. defectively centred.]