icycloidal 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.

Qualities of Building
Stone.--The principal qualities of a good building stone are--(1)
Strength, (2) hardness, (3) durability, (4) appearance, (5) facility
for working. There are also other mino