To Find: Multiply the diameter in inches at the small end by one-half the number of inches, and again multiply this product by the length of the log in feet; this product divided by 12 will give the number of feet of one-inch boards the log will make. HORSE-POWER OF BOILERS. For horizontal, tubular and flue boilers, divide the number of feet of heating surface by 15; this will give the horse-power. A cord of pine wood weighing 2,000 pounds is about equal to 1,000 pounds of soft coal for steam purposes. Each foot of grate should burn 20 pounds of soft coal, or 40 of wood, per hour, with a natural draught. HORSE-POWER OF AN ENGINE. Multiply the area of the cylinder in square inches by the average effective pressure in pounds to the square inch, deducting three pounds per square inch for friction. Multiply this remainder by the speed of the piston in feet per minute, and divide by 33,000. The quotient will be the true horse-power. HORSE-POWER OF PELTON WHEEL. The Pelton wheel is in high favor with California miners. When the head of water is known in feet, multiply by 0.0024147 and the product is the horse-power that one miner's inch of water will give. ASSAYING. The muffle furnaces of the Morgan Crucible Company of Battersea are favorably known. The most useful size is that taking a "D" Muffle, 8-1/2 inches by 5 inches by 3-1/4 inches. A CHEAP "TESTING" OUTFIT. Sometimes the pioneer is forced to attempt a good many investigations with very simple apparatus. Should he possess the following, he can achieve much: A spirit lamp, candle, blow-pipe, magnet, a bottle of hydrochloric acid, quart glass jar, three test tubes with corks, two feet of glass tubing (hard glass), copper wire, two square inches of tin plate, forceps and test paper. Such an outfit could certainly be bought for $1. WEIGHT OF EARTH, SAND, GRAVEL, ETC. A ton of shingle averages 23 cubic feet. A ton of pit sand averages 22 cubic feet. A ton of earth averages 21 cubic feet. A ton of river sand averages 19 cubic feet. A ton of coarse gravel averages 19 cubic feet. A ton of clay averages 18 cubic feet. A ton of marl averages 18 cubic feet. A ton of chalk averages 14 cubic feet. WEIGHTS OF ORES AND ROCKS. Quartz, 162 pounds a cubic foot; silver glance, 455 pounds; ruby silver, 362; brittle silver, 386; horn silver, 345; antimony glance, 287; cinnabar, 549; copper pyrites, 262; gray copper, 280; galena, 461; zinc blende, 249; iron pyrites, 312; limestone, 174; clay, 162. CALIFORNIA PUMP.