Q. _Why is the TOP of a MOUNTAIN COLDER than the VALLEY beneath, although it be two or three miles nearer to the sun?_ A. 1st--Because the air on a mountain is _less compressed_, than the air in a valley. 2ndly--It is _more rarefied_: and 3rdly--It is _less heated by reflection_. Q. _Why is air COLDER on a mountain "because it is LESS COMPRESSED?"_ A. As the air in a _valley_ is more compressed (by the mass of air above) than that on the top of a _mountain_, therefore _more heat runs out_; just as more water runs from a sponge, the closer it is _squeezed together_. Q. _Why is a mountain-top COLDER than a valley, "because the AIR there is MORE RAREFIED?"_ A. As the air is _more rarefied_, its heat is _diffused over a larger space_ and is _less_ intense; just as a candle would _show less light_ in a _large_ room, than in a _small_ one. Q. _Why is a mountain-top COLDER than a valley, "because the AIR there is LESS HEATED by REFLECTION?"_ A. Air is _not_ heated by the _sun_, but by _reflection from the surface of the earth_; and as there is _no earth_ round a _mountain-top_ to reflect heat, therefore the air there is intensely cold. Q. _Why does RUBBING our HANDS and FACES make them feel WARM?_ A. Chiefly because the friction _excites the latent heat_ of our hands and faces, and makes it sensible to our feeling. Q. _When a man has been almost DROWNED, why is suspended animation RESTORED by RUBBING?_ A. The vital heat of the body (which had become _latent_ by the action of the water) is _again developed by friction_: and, as soon as this animal heat can be excited, the vital powers of the body are restored. Q. _Why do two pieces of ICE (rubbed together) MELT?_ A. Ice contains 140 _degrees of latent heat_, and (when two pieces are _rubbed together)_ their _particles are compressed_, and this _latent heat_ rolls out and _melts the ice_. Q. _Are not FORESTS sometimes SET on FIRE by friction?_ A. Yes; when two branches or trunks of trees (blown about by the wind) _rub violently against each other_, their _latent heat is developed_, and sets fire to the forest. Q. _What is meant by COMPRESSION?_ A. The act of _bringing parts nearer together_; as a sponge is _compressed_ by being _squeezed in the hand_. Q. _Cannot HEAT be evolved from common air merely by COMPRESSION?_ A. Yes; if a piece of _German tinder_ be placed at the _bottom of a glass tube_, and the air in the tube _compressed by a piston_,[11] the tinder will catch fire. [11] In a common syringe or squirt, the _handle_ part which _contains the sucker_ (and is forced up and down), is called "The Piston." Q. _Why will the tinder catch fire?_ A. Because the _air is compressed_; and its _latent heat being squeezed out_, sets fire to the tinder at the bottom of the tube. CHAPTER IX. EFFECTS OF HEAT. 1.--EXPANSION. Q. _What are the principal EFFECTS of HEAT?_ A. 1.--Expansion. 2.--Liquefaction. 3.--Vaporization. 4.--Evaporation; and 5.--Ignition.