Curiosities of Heat

ubserve none of those uses to which it is now applied in the economy of Nature or in the works and arts of man. But heat passes from place to place with great facility, and by one meth

from body to body by 'conduction,'

nsel, by the 'con

tom and from particle to particle t

n Peter to give some illustrati

ole length of the pin and burns my fingers. The parts of a stove which touch the fire are first heated, and from them the heat spreads through the whole stove. A pine-wood shaving, kindled at one end, is heated by conducti

nd moistens the whole of it. We must remember that the transfer of heat is not a transfer of any substance, but a transfer of motion. One atom is set in motion, and strikes against another atom and sets that in motio

es are called good conductors, because heat permeates them so readily and rapidly;

he other. The child very soon learns to know the different feeling of a cotton night-gown from one of flannel, and the difference in apparent warmth between a linen pillow-case and a woolen blanket. After a room has been heated for a considerable time the various objects in it all become of the same temperature

we receive heat rapidly from it, it feels to us very hot. Or if it be colder than our bodies, it takes heat from our hands very rapidly, and gives the impression of

rs than fluids, and fluids are better conductors than gases, and among solids the metals are better conductors than organized bodies, like wood or flesh, and better than the loose and porous minerals. In bodies of loose, porous, or fibrous texture, the continuity of the conductory sub

n winter. Their roots reach down into the earth, which remains warm in the coldest weather. This heat of the earth travels along the fibres up through the tree, while the heat conducted across the fibres escapes much more slowly into the open air. The bark also, being a very bad conductor, hinders the escape of heat. O

hod by which heat passe

iated," re

t is rad

rom a hot body heat is passing off in straight lines in every dire

nd. It also follows the same general principles as light in all its motions. It is absorbed, reflected, or transmitted in the same m

ere are good and bad radiators of heat. The r

The higher the temperature, the more

. A dull, rough surface radiates heat more

and bright, some substances radiate heat much better than others. A surface

you can, explain the

adiation is conduction through that subtle e

bstances. Heat, light, and electricity are supposed to be all propagated through the same theoretical ether. Sir Isaac Newton estimated the density of the ether as seventy thousand times less than the density of our atmosphere, and its elasticity in proportion to its density as four hundred and ninety millions times gre

method by which heat pas

on," was

nt by convec

If I remove a hot iron or a kettle of hot water,

aining the water; as fast as the water at the bottom next the fire is heated, it rises and carries the heat to the top; cold water comes to take its place, and this in tur

ry heat enough to warm a continent, and the mighty ocean currents are still

stand. When radiant heat falls

according to the same principles by which light is reflected; or it may be transm

is reflected from a polished surface, such as a lamp reflector: heat is reflected in the same man

n like manner radiates through certain solids. Luminous heat is radiated through glass. Rock-salt transmits dark heat also. A plate of alum permits light to pass, but stops both luminous heat and dark heat. Remember that transmitted heat, as was said

s hold an inverse ratio to each other; the better the reflecting qualities, the worse the absorbing, and the worse the reflecting, the better the absorbing. Heat which is absor

el, which is absorbed by a bod

lled late

mon expression, but what

at, as you suggested in your first question, is that heat which

dies. We must not suppose, however, that this latent heat continues to exist in bodies as heat; latent heat is that heat which is converted into force or so

of ice water through one hundred and forty degrees, and by receiving that heat it is melted, but the water produced has the temperature of thirty-two degrees. It has received one hundred and forty degrees o

a gas. About one thousand degrees of heat is thus expended, but the steam which is produced has only the temperature of two hundred and twelve degrees. If the process be reversed, the steam gives up, as it is said, the one thousand degrees of heat in returning to the condition of water and the one hundred and forty degrees in resuming the crystalline structure of ice. The heat which was employed as force

t of the sun beams upon the ocean; the greater part of that heat is expended as force in overcoming the molecular attraction of water, thus converting it to vapor, and in raising tha

e 1

ave no better methods of kindling fire rub dry wood together till the sticks ignite. The force expended in overcoming the friction is changed to heat. In the combustion of coal beneath the steam boiler we see both processes going on. The atoms of carbon dash against the atoms of oxygen, and the force of the coll

many and various careful experiments, Dr. Joule demonstrated that 772 units of force are the equivalent of one unit of heat. A pound weight falling 772 feet, or 772 pounds falling one foot, and then arrested, produces heat sufficient to raise one pound of water one degree. The result is the same whatever the method by which the force is expended. If water be agitated or s

degree, sets free an amount of hydrogen which, when burned, raises exactly one pound of water one degree. Again, the same amount of electricity will produce an attractive magnetic force by which a weight of

e we explain the production of heat by compression and the loss of

s; if it be expanded, cold is produced. Since gases expand or yield to p

the operation be sudden or slow, but if the compression or expansion be slow, the heat or cold generated is less apparent; the hea

explain

n the gas, and appears again in the form of atomic heat motion. In the expansion of gases the operation is just the reverse; the atomic heat motion i

that is, specific heat. What is understo

nt substances require to raise their tempe

erature in five pounds of sulphur, or four pounds of air, or nine pounds of iron, or eleven pounds of copper, or thirty pounds of mercury, lead, or gold. This is what is meant by saying that one substance has a greater capacity for heat than another. The specific heat of water is greater than that of a

ific heat depends upon the number of atoms, that it holds an inverse ratio to their combining numbers, or, what is the same thing, a direct ratio to the number of atoms. This would ha

ng review of your academic studies has not wearied you of the very word heat and wor

e are not in the habit of becom

that the lessons to come will prove more interesting still. Next week we shall c

or others, that they might understand the wonderful works of God which we shall now proceed to examine. And, reader, do not forget that heat itself, that subtle motion and mighty force, with all its laws and principles, is one of God's works. Already have we been looking at the Creator's handiwork. Alrea