Question 12.—­State what are the conditions favourable for the formation of dew.  Describe an instrument for determining the dew point, and the method of using it.

Answer.—­This is easily proved from question 1.  A body of gas as it ascends expands, cools, and deposits moisture; so if you walk up a hill the body of gas inside you expands, gives its heat to you, and deposits its moisture in the form of dew or common sweat.  Hence these are the favourable conditions; and moreover it explains why you get warm by ascending a hill, in opposition to the well-known law of the Conservation of Energy.

Question 13.—­On freezing water in a glass tube, the tube sometimes breaks.  Why is this?  An iceberg floats with 1,000,000 tons of ice above the water line.  About how many tons are below the water line? p 180

Answer.—­The water breaks the tube because of capallarity.  The iceberg floats on the top because it is lighter, hence no tons are below the water line.  Another reason is that an iceberg cannot exceed 1,000,000 tons in weight:  hence if this much is above water, none is below.  Ice is exceptional to all other bodies except bismuth.  All other bodies have 1090 feet below the surface and 2 feet extra for every degree centigrade.  If it were not for this, all fish would die, and the earth be held in an iron grip.

P.S.—­When I say 1090 feet, I mean 1090 feet per second.

Question 14.—­If you were to pour a pound of molten lead and a pound of molten iron, each at the temperature of its melting point, upon two blocks of ice, which would melt the most ice, and why?

Answer.—­This question relates to diathermancy.  Iron is said to be a diathermanous body (from dia, through, and thermo, I heat), meaning that it gets heated through and through, and accordingly contains a large quantity of real heat.  Lead is said to be an athermanous body p 181(from a, privative, and thermo, I heat), meaning that it gets heated secretly or in a latent manner.  Hence the answer to this question depends on which will get the best of it, the real heat of the iron or the latent heat of the lead.  Probably the iron will smite furthest into the ice, as molten iron is white and glowing, while melted lead is dull.

Question 21.—­A hollow indiarubber ball full of air is suspended on one arm of a balance and weighed in air.  The whole is then covered by the receiver of an air pump.  Explain what will happen as the air in the receiver is exhausted.

Answer.—­The ball would expand and entirely fill the vessell, driving out all before it.  The balance being of greater density than the rest would be the last to go, but in the end its inertia would be overcome and all would be expelled, and there would be a perfect vacuum.  The ball would then burst, but you would not be aware of the fact on account of the loudness of a sound varying with the density of the place in which it is generated, and not on that in which it is heard. p 182