These can readily be made, if not provided, by cutting out a disc of cardboard to fit snugly either the spring collar just in front of a positive eyepiece or the eyepiece itself at the diaphragm, if an ordinary Huygenian. Rule two diametral lines on the circle struck for cutting the cardboard, crossing at the center, cut out the central aperture, and then very carefully stretch over it, guided by the diametral lines, two very fine threads or wires made fast with wax or shellac. [Illustration: FIG. 168.—Clark 5-inch with Tripod and Pier.] Now pointing the telescope at the most distant well defined object in view, rotate the spring collar or ocular, when, if the crossing of the threads is central, their intersection should stay on the object. If not shift a thread cautiously until the error is corrected. Keeping the intersection set on the object by clamping the tube, one turns attention to the finder. Either the whole tube is adjustable in its supports or the cross-wires are capable of adjustment by screws just in front of the eyepiece. In either case finder tube or cross-wires should be shifted until the latter bear squarely upon the object which is in line with the cross threads of the main telescope. Then the adjusting screws should be tightened, and the finder is in correct alignment. As to adjustments 1 and 3, in default of circles the ordinary astronomical methods are not available, but a pretty close approximation can be made by levelling. A good machinist’s level is quite sensitive and reliable. The writer has one picked out of stock at a hardware shop that is plainly sensitive to 2′ of arc, although the whole affair is but four inches long. Most mounts like the one of Fig. 168 have a mark ruled on the support of the polar axis and a latitude scale on one of the cheek pieces. Adjustment of the polar axis to the correct altitude is then made by placing the level on the declination axis, or any other convenient place, bringing it to a level, and then adjusting the tripod until the equatorial head can be revolved without disturbing this level. Then set the polar axis to the correct latitude and adjustment number 1 is complete for the purpose in hand. Lacking a latitude scale, it is good judgment to mark out the latitude by the help of the level and a paper protractor. To do this level the polar axis to the horizontal, level the telescope tube also, and clamp it in declination to maintain it parallel. Then fix the protractor to a bit of wood tied or screwed to the telescope support, drop a thin thread plumb line from a pin driven into the wood, the declination axis being still clamped, note the protractor reading, and then raise the polar axis by the amount of the latitude. Next, with a knife blade scratch a conspicuous reference line on the sleeve of the polar axis and its support so that when the equatorial head is again levelled carefully you can set approximately to the latitude at once.