The Largest Wheel of Its Kind Ever Made in the World.—­The greatest wheel of its kind in the world, a very wonder in mechanism, was built for the Calumet and Hecla Mining Company of Lake Superior, Mich., for the purpose of lifting and discharging the “tailings,” a waste from the copper mines, into the lake.  Its diameter is 54 feet; weight in active operation, 200 tons.  Its extreme dimensions are 54 feet in diameter.  Some idea of its enormous capacity can be formed from the fact that it receives and elevates sufficient sand every twenty-four hours to cover an acre of ground a foot deep.  It is armed on its outer edge with 432 teeth, 4.71 inches pitch and 18 inches face.  The gear segments, eighteen in number, are made of gun iron, and the teeth are machine-cut, epicycloidal in form.  It took two of the most perfect machines in the world 100 days and nights to cut the teeth alone, and the finish is as smooth as glass.  The wheel is driven by a pinion of gun iron containing 33 teeth of equal pitch and face and runs at a speed of 6OO feet per minute at the inner edge, where it is equipped with 448 steel buckets that lift the “tailings” as the machine revolves and discharges them into launders that carry them into the lake.  The shaft of the wheel is of gun iron, and its journals are 22 inches in diameter by 3 feet 4 inches long.  The shaft is made in three sections and is 30 inches in diameter in the center.  At a first glance the great wheel looks like an exaggerated bicycle wheel, and it is constructed much on the same principle, with straining rods that run to centers cast on the outer sections of the shaft.  The steel buckets on either side of the gear are each 4 feet 5-1/2 inches long and 21 inches deep, and the combined lifting capacity of the 448, running at a speed of 600 feet per minute, will be 3,000,000 gallons of water and 2,000 tons of sand every twenty-four hours.  The mammoth wheel is supported on two massive adjustable pedestals of cast iron weighing twelve tons each, and its cost at the copper mines before making a single revolution, $100,000.

Strength of Brick Walls.—­The question of strength of brick walls is often discussed, and differences of opinion expressed.  The following is one of the rules given:—­For first-class buildings, with good workmanship, the general average should not exceed a greater number of feet in height than three times its thickness of wall in inches, and the length not to exceed double the height, without lateral supports of walls, buttresses, etc., as follows for safety: 

      THICKNESS; SAFE HEIGHT; LENGTH.

8-1/2 inch walls; 25 feet; 50 feet. 13 inch walls; 40 feet; 80 feet. 17 inch walls; 55 feet; 110 feet. 22 inch walls; 66 feet; 130 feet. 26 inch walls; 78 feet; 150 feet.

Where the lengths must exceed these proportions, as in depots, warehouses, etc., the thickness should be increased, or lateral braces instituted as frequently as practicable.