1. Set up vertically a stick of known length, and measure the length of its shadow upon a horizontal or other plane; measure also the length of the shadow thrown by the object whose height is required. Then it will be:--As the length of the stick’s shadow is to the length of the stick itself, so is the length of the shadow of the object to the object’s height. _By Reflection._ Place a vessel of water upon the ground and recede from it until you see the top of the object reflected from the surface of the water. Then it will be:--As your horizontal distance from the point of reflection is to the height of your eye above the reflecting surface, so is the horizontal distance of the foot of the object from the vessel to its altitude above the said surface. _Instrumentally._ Read the vertical angle, and multiply its natural tangent by the distance between instrument and foot of object; the result is the height. When much accuracy is not required vertical angles can be measured by means of a quadrant of simple construction, represented in Fig. 46. The arc AB is a quadrant, graduated in degrees from B to A; C, the point from which the plummet P is suspended, being the centre of the quadrant. [Illustration: FIG. 46.] _When_ the sights AC are directed towards any object, S, the degrees in the arc, BP, are the measure of the angle of elevation, SAD, of the object. TO FIND THE DEPTH OF A SHAFT. _Rule_:--Square the number of seconds a stone takes to reach the bottom and multiply by 16. Thus, if a stone takes 5 seconds to fall to the bottom of a shaft-- 5² = 25; and 25 × 16 = 400 feet, the required depth of shaft. DESCRIPTION OF PLAN FOR RE-USING WATER. Where water is scarce it may be necessary to use it repeatedly. In a case of this kind in Egypt, the Arab miners have adopted an ingenious method, which is shown in Fig. 47, and may be adapted to almost any set of conditions. At _a_ is a sump or water-pit; _b_ is an inclined plane on which the mineral is washed and whence the water escapes into a tank _c_; _d_ is a conduit for taking the water back to _a_; _e_ is a conduit or lever pump for raising the water. A certain amount of filtration could easily be managed during the passage from _c_ to _a_. [Illustration: FIG. 47.] COOLING COMPOUND FOR HEATED BEARINGS. Mercurial ointment mixed with black cylinder oil and applied every quarter of an hour, or as often as expedient. The following is also recommended as a good cooling compound for heavy bearings:--Tallow 2 lb., plumbago 6 oz., sugar of lead 4 oz. Melt the tallow with gentle heat and add the other ingredients, stirring until cold. CLEANING GREASY PLUMMER BLOCKS.