Curiosities of Heat

it was left the previous L

variety in the experience of life; the warmth of summer ripens the fruit and grain, and the cold of winter tones up the physical strength; nay, the winter's frost is a natural subsoiler, loosening up the hard earth and promoting vegetable growth. As for man's higher interests, no one can tell how much the world is indebted to winter evenings, to a period of darkness longer than is needed for sleep, and a period of cold during which the work of h

tation of the earth brings every place by turns under the influence of the sun's rays, and in turn withdraws it from t

e answered. "Mr. Hume, I should be g

during the day and the radiation of that heat during the night; and, secondly, t

ind the horizon; the supply of heat is cut off and the temperature begins to fall. Then all those objects which during the day were laying up heat in store begin to radiate heat into the air, and by their contact with it keep up its warmth. Commonly, the temperature falls so low that bodies radiate more heat than they absorb before the setting of the sun. In this process wat

vapor than to raise it from the freezing to the boiling point; that is, about one thousand degrees of heat are required to turn boiling hot water to vapor. The same amount of heat is required for the formation of vapor whatever the temperature of the water from which the vapor rises. There is only this difference-vapor from cold water is cold, while vapor from hot water is hot. Evaporation goes on more rapidly in proportion as the temperature

hundred and twelve degrees nearly thirty-four feet; that is, vapor at two hundred and twelve degrees has an elastic force of fifteen pounds to the square inch. Let us suppose that at sunrise the air has a temperature of thirty-six degrees, and that as much vapor is already formed as can sustain itself at that temperature. As the sun sheds down his rays the temperature rises and more vapor is formed. We will suppose that half an inch of water is evaporated. Some of this vapor will be carried by ascending currents of air into the higher regions and condensed into clouds, some will be carried by winds into drier and warmer regions, yet the amount of vapor will increase during the day. We will suppose that during the night the temperature falls again to thirty-six degrees; all the excess of vapor above two inches and two-thirds of water will be condensed and become dew or fog, and in this condensation the thousand degrees of heat absorbed in the formation of the vapor will be given out again. If vapor equal to one inch of water be condensed, heat is set free sufficient to boil a sheet of ice water, five and a half inches in thickness, extending over the whole region; that is, it would be all the same as if a fire were kindled on every square rod of land hot enough to boil during the night more than twenty barre

ver heard the 'dew

sir, I

w what is m

f temperature at which

oes the dew

ount of vapo

ld exist, any diminution of the temperature must, of course, cause dew to be

ir, I

er or goblet whose outer surface has been wiped perfectly dry, and polished. Into this set a common thermometer. Cool down this warm water by dropping into it small pieces of ice, and notice carefully when the polished glass begins to be dimmed as if it had

out the formation of dew which I do not under

r your questions, and wi

ar nights, but not very often on clou

ether cloudy nights or cl

er, I think, but I never could s

spread over a tomato vine ke

upon the paper instead

he dew-for frost is nothing but dew frozen as

dew fall upon t

ve the dew point, or till the vapor is so far exhausted that the dew point falls below the existing temperature. Dew is formed upon the upper surface and not upon the under, because the upper surface is cool and the under surface is warmer. Beneath the paper spread over the tomato vine, the earth is radiating heat and the paper is radiating it back again. If the paper were not there, the heat would be radiated into space and not returned again. The vine woul

r, "that clouds were of any grea

reat use in warming the earth in other ways, as well as by serving a

-I mean, is formed-on grass and lea

u ever see barefoot boys running in the cold dew stop

; I have don

ou stand u

arned that the ro

have but little heat, and that little they part with rapidly. The rocks and stones, on the other hand, are bulky, and contain a much larger store of heat, their radiating surface is comparatively small; only one s

day to night and from night to day. But upon the sea-coast and upon certain islands

Hume said: "I suppose, of course, that

warmer. Then a breeze springs up in the opposite direction; the cooler air of the land flows out upon the sea. By this means the air upon the land and the air upon the sea are daily commingled, thus securing a more even temperature upon the lan

being of his creatures. 'Day unto day uttereth speech and night unto night showeth knowledge. There is no speech nor language where their voice is not heard.' This care for the earthly well-being of men is but a type of his care for their spiritual happiness. The plan of salvation, and the ways of divine providence wo