n with increased pressure,
this effect will be more appreciable when the area and travel of slide
valve are in excess.

(15) J.M.T. asks: Is there friction between two bodies while at rest,
or only when one or both are in motion? A. Both when at rest and in
motion.

Why does a balloon rise in the air? A. See p. 64, vol. 32.

(16) S.J.S. asks: 1. How are augers twisted? A. By special machinery.
2. How are twist drills made, and are they single or double grooved?
A. They are double grooved or double twisted, and are cut out in a
milling machine.

Can weights, springs, or water from a tank be used to any advantage to
run a lathe? A. No.

How much do iron and brass, in rods or bands, expand in length when
heated to red heat? A. Iron about 1/8 inch per foot, brass 1/10 inch.

Is the pressure of the air to be added to the weight of water in the
bottom of a vessel in estimating the pressure on the bottom? A. No.

Does a watch or clock run faster when just wound up? A. No.

Is it not moisture in the air that makes it heavier, and so affects
the barometer? A. Yes.

Is the pressure in a siphon equal throughout, or is it greater in the
upper end? A. Equal throughout.

Will it take more power to run two millstones in opposite directions
than it will to run one at the same speed, the other being stationary?
A. Yes, it will take double the power.

1. How are common screws made? A. In lathes, with tools and dies. 2.
How can I make wooden screws perfectly smooth? A. By using keen tools.

What is the simplest way of cutting a square hole in a bar of iron? A.
Drill a round hole and square it out.

(17) G.E.C. asks: Could I have a brick range 2x3 feet, built on a
platform about 1 foot from floor, with two compartments, to be heated
with petroleum, the lower one to be used as an oven, the upper one to
have a stove top to set cooking utensils on, and have a ventilating
pipe run from each compartment of the oil receptacles into the place
in the chimney where the stove pipe usually goes, to carry away any
gas or smoke? I want the oil receptacles to be arranged to be drawn
out, to be filled and trimmed, and I would like four burners to heat
an oven 22 inches square, as hot as the same oven could be heated with
wood. A. We doubt the propriety or the economy of substituting oil for
wood, but something may be done to make the atmosphere of kitchens
more endurable in summer, and permanently so in warm climates. A
double faced rang