Joseph C. Martindale

“ What is a vacuum?
A vacuum is a place that does not contain anything, not even air.
When a vessel contains water and we pour the water out, does that produce a vacuum?
No; because air passes in and fills the vessel.
How then can a vacuum be produced?
A vacuum in any place, can be produced only by drawing the air out of it.
When a vacuum is produced, what does the surrounding air try to do?
It tries to get in so as to fill the vacuum.
With what force does the air try to fill a vacuum?
With a force of fifteen pounds on every square inch of surface. ”

“ What effect does warm air have on sound?
Sound travels more rapidly in warm air.
How much does heat increase the velocity of sound?
The velocity of sound is increased one foot in a second of time, for every degree of heat added to the air; so that sound travels eleven hundred and twenty feet in a second, when the temperature is at sixty-two degrees, which is nearly one mile in five seconds.
Does light travel more rapidly than sound?
Yes; light comes from the moon to the earth, a distance of two hundred and forty thousand miles, while sound moves eleven hundred and twenty feet. ”

“ Why does a person standing up in a wagon fall when the wagon is suddenly stopped?
Because the feet, being in contact with the wagon, are suddenly stopped, while the body still moves forward, thus throwing the line of gravity ahead of the feet; hence, the person must fall, unless supported.
Why do animals with four feet stand firmer than those with only two feet?
Because the four feet afford a larger base to stand upon than the two feet do, and, therefore, support the centre of gravity better. ”

“ Why are sounds heard better at night than in the day?
Because the air at night is condensed by cold, and becomes a better conductor of sound; also, because the nights are stiller, and fewer sounds take our attention.
Why is moist or damp air a better conductor of sound than dry air?
Because the particles of water in the damp air increase its power of conduction.
Why is sound heard farther when over the water?
Because the damp air over the water is a better conductor, and because it contains fewer objects to obstruct the waves of sound. ”

“ When does lightning pass from one cloud to another cloud?
Whenever one cloud becomes filled with more electricity than another, the cloud having the most electricity gives off a portion to the cloud having the least electricity. ”

“ The babbling of the brook, the roaring of the cataract, the wailing of the wind, and the singing of the birds, everywhere show the Divine love of harmony; for where there is no human ear to listen, they still sing their heavenly anthems of praise to His ear alone. ”

“ It is the gradual change of a liquid into a vapor.
When water is left in a shallow vessel, what becomes of it?
The water evaporates or passes off into the air.
Do liquids generally evaporate?
Yes; when exposed to the air, nearly all liquids evaporate.
Does water change into steam when it evaporates?
Water does not change into steam when it evaporates.
How, then, does water evaporate?
It passes off into the air in particles or drops so very small as not to be visible.
Is evaporation always going on around us?
Yes; wherever there is water exposed to the air, evaporation is taking place. ”

“ When the earth turns over, can any substance fall away from its surface?
No; all things are drawn to the earth with so much force that they cannot fall away.
Upon what does the weight of a body depend?
The weight of a body depends upon the force with which it is drawn towards the earth.
143 What kind of substances are attracted with the most force?
Those that are the most dense, like the metals; hence, they are the heaviest.
What causes a liquid to form into a drop at the mouth of a bottle?
The attraction of cohesion causes the drop to be formed.
What causes the drop to fall to the earth? ”

“ When a fire is made in a room, why does the furniture often make a snapping noise?
Because heat expands the wood, and the particles make a snapping noise upon separating.
Why does a stove make a crackling noise as it grows hot?
The particles of the iron make the noise in expanding. ”

“ When the vapor is condensed higher up in the air, what does it produce?
It produces a cloud.
What is a cloud?
A cloud is only a fog, higher up in the air.
Do fogs ever ascend in the air?
Yes; they often ascend, and thus produce clouds.
What causes the vapor of the air to be condensed into clouds?
Cold causes it to be condensed into clouds.
Does the air grow colder as we ascend?
Yes; the higher we ascend, the colder we find the atmosphere.
What becomes of the vapor in the air, as it ascends from the earth?
The vapor is condensed into clouds in the upper regions of the air. ”

“ Because the same liquid is expanded and takes up more room, although it has no more weight.
Why will a gallon of cold water weigh more than a gallon of hot water?
Because a gallon of cold water, when heated, will make more than a gallon of hot water.
When do we get the most molasses, by buying it in hot or in cold weather?
We get the most by buying it in cold weather, because a gallon bought then will make more than a gallon when the weather becomes warmer.
Does heat expand the air and make it lighter?
Heat does expand the air and make it lighter. ”

“ When the pump-handle is lowered, the water, above 91 the valve or bucket attached to the end of the rod, is raised so that it runs out at the spout; and the vacuum, thus produced by raising the water, is filled by the water in the well, which is forced up the pump-tube by the pressure of the air. When the pump is at rest, the lower valve, which is air-tight, prevents the water from sinking back into the well, so that the pump-tube is always full of water, whether we are pumping or not. ”

“ What may we remember about heat?
And God said, Let there be light; and there was light. But along with the light, came its companion—heat; for when the sunbeam first came forth at His command, the twin sisters, light and heat, together touched the earth, causing it to bloom with life and beauty. And the earth brought forth grass, the herb yielded its seed, and the tree its fruit: And God saw that it was all good.
77
CHAPTER IV.
The Air.
Where do we find air?
We find air everywhere around the earth.
Does the air fill every place?
The air fills every place not filled by some other substance. ”

“ The ice is changed into water.
Is water a liquid?
Water is a liquid.
How then can a solid be changed to a liquid?
By applying heat to a solid, it may be changed to a liquid.
What is meant by liquefaction?
Liquefaction is the changing of a solid to a liquid, by heat.
How may tallow be melted?
By heating the tallow, it may be melted.
Will the tallow become hard again when cold?
It will be hard again when cold.
Can lead and other metals be melted?
They can be melted or changed to a liquid state by heat.
Can all solids be changed to liquids? ”

“ In presenting these Familiar Lessons in Natural Philosophy to the youth of our country, it is with the earnest hope that it may make them better acquainted with the natural objects surrounding us; that it may lead them to observe the order, the harmony, and the beauty in nature everywhere ”

“ At one end of the telegraph wire is an electrical battery, and at the other end is an electro-magnet. When a message is to be sent, the electricity is transmitted through the wire to the soft iron of the electro-magnet, which causes the iron to move, and this motion is conveyed to the machinery, which is needed to print the message in letters or signals, so as to be understood.
Does electricity move rapidly?
Yes; its velocity is such as to move around the earth in a quarter of a second. ”

“ Because every turn in the pipe increases the friction made by the water.
Why does a wagon-wheel turn around when the wagon moves?
Because the friction between the wheel and the earth, prevents the wheel from sliding along.
Why can a steam-engine draw a train of heavy cars?
Because the friction, between the wheels and the rails, causes the wheels to turn around instead of sliding; and thus the engine moves forward drawing the cars with it. ”

“ The weight is the large body hanging from the short arm of the lever.
What is the power?
The power is the smaller body hanging from the long arm of the lever.
In Fig. 45, the distance from the fulcrum to the power is ten times the distance from the fulcrum to the weight; now, if the small body weighs one pound, how much must the large body weigh, so as to balance it?
The large body must weigh ten pounds.
When the small body weighs ten pounds, how much must the large body weigh, so as to balance it?
The large body must weigh ten times as much, or one hundred pounds. ”

“ Because the air in the snow makes it a poor conductor 115 of heat, so that it prevents the warmth of the earth from passing off into the air. Snow is, therefore, a protection to the plants, and prevents their being frozen by the cold weather of winter. ”

“ Simple truths in natural science may be learned at an early age; for it requires no more than the ordinary intelligence possessed by boys and girls to understand them. Such facts are not only valuable in themselves, but they are also useful in disciplining the mind by teaching it to observe the many changes constantly going on around us, and to reason and reflect in regard to the same. Habits of observation and reflection thus formed are likely to go with us through life ”

“ When cork is put in water, why does it rise to the surface?
Because the cork is lighter than an equal bulk of water.
Does heat increase the weight of any substance?
Heat does not increase the weight of any substance. ”

“ They open a valve at the top of the balloon, which permits some of the gas to escape; then it will sink towards the earth.
How is the valve at the top of the balloon opened and closed?
It is opened and closed by means of small ropes, reaching from the valve to the car beneath.
Can the balloon be made to go in any one direction?
No; it is carried about by the currents of air, and those in the car cannot control its course; therefore, it has never been of much use to man.
96 Winds. What is wind?
Wind is air moving from one place to another.
Does the air move in every direction? ”

“ What other substance will act the same as the sealing-wax?
A dry glass tube will act in the same manner when rubbed.
Where is electricity found?
Electricity is found in every body, and in every thing.
184 How is electricity developed?
Electricity is developed by motion, by friction, and by almost every change that takes place.
Is electricity found in the air?
Yes; the air is almost constantly electrified.
With what is electricity often accompanied?
Electricity is often accompanied by heat and light. ”