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CONVERSATION VIII.

AIR.

WATER, Father, by evaporation, must make a very large part of the atmosphere.

It evidently does; as the clouds, which often cover the face of the heavens, abundantly prove.

Since our last conversation, Father, I have read the account of Dr. Watson's experiment in reference to evaporation. Is it not surprising!

I do not recollect the particulars; , can you repeat them?

Here, Father, I have copied the account into my pocket book. Shall I read it ? Do, Frank.

FRANK. < An acre of ground, burnt up by the sun, dispersed into the air sixteen hundred gallons of water, in the space of twelve of the hottest hours of the day. I put a glass, mouth downward, on a grass plot, on which it had not rained for above a month. In less than two minutes, the inside was covered with vapor; and in half an hour drops began to trickle down its inside. The mouth of the glass was twenty square inches. There are 1296 square inches in a square yard, and 4840 in an acre. When the glass had stood a quarter of an hour,

I wiped it with a piece of muslin, the weight of which had been previously taken. As soon as the glass had been wiped dry, the muslin was weighed again: the quantity collected was,

six grains, in a quarter of an hour, from twenty square inches of earth; a quantity equal to 1600 gallons from an acre, in twenty-four hours,

Another experiment, after rain had fallen, gave a much larger quantity.

This is a pleasing and satisfactory experiment. Does Watson mention how much space an inch of water occupies, when it is turned into vapor ?

I think not; do you know, Father ?
Yes, Frank; more than two thousand inches.

You said, Father, that water was composed of two kinds of air.

I have separated water into these different kinds of air. The air we breathe, is formed of two gasses, called oxygen and nitrogen. If we were to collect twenty-five measures of common air, about five would be oxygen, and twenty would be nitrogen.

What is the difference, Father ?

It is very great; without oxygen, nothing would burn, and nothing could live. A lighted match put into oxygen

burns with great brilliancy; if put inte nitrogen, it is as soon extinguished as if put into water; an animal put into it, dies instantly.

It would be a good thing, Father, then if the air were all oxygen.

By no means ; God has formed every thing with the highest wisdom. If we were to breathe oxygen only, life would soon become extinct. It would be so great a stimulent, that the human frame could not long sustain it. I saw a young gentleman breathe it the other day from a bladder, but he was very unwell for some days after the experiment, and his life was in danger. To breathe nitrogen alone would be instant death.

Then if God were to take away the oxygen, all mankind, and every living thing would die.

They would. It is necessary to our health, that they should be mingled, as they are, with exquisite skill. Truly, as it is said in Scripture, in God, or by his power and goodness, we every instant, “ live, and move, and have our being."

Father, you have not said any thing about the weight of the air; it must have weight, like every thing else. Has it not ?

Indeed it has ; the mercury in the barometer rises or falls, as the air is heavy or light.

And the air-pump, Father, proves that it has great weigin

Certainly, it doos. And we can ascertain the pressure of the an, by the common pump. The weight of the atmosphere supports a column of water of about thirty four feet and a half high. Now the cubic foot of water weighs one thousand ounces, or sixty-two poands and

AIR.

a half. What then is the weight of the column of water, which the pressure of the atmosphere balances ?

Let me see ; that will be thirty-four times and a half, sixty-two and a half; that will be equal to 2158 pounds.

The one hundredth and forty-fourth part of this will be the weight of the air on every square inch. What is it? I am sure you can tell me.

Fifteen pounds. What a weight it must be, Father, on the whole earth.

It must, indeed. Mr. Cotes made an inquiry on this subject, the result of which was, that it is equal to a globe of lead sixty miles in diameter; which arnounts to a pressure equal to five thousand millions of millions of tons.

Does the air press on me, at the rate of fifteen pounds for every square inch of my body? I don't feel that it does, Father.

But it does ; and the reason you do not feel it, is, because it is counteracted by the air that is within you. On every square inch there is a pressure of fifteen pounds ; on every square foot, then, there will be 144 times as much, or 2160 pounds; and if we suppose, that there are fifteen square

feet on a man's body, how much will the weight be? The answer, Frank, I think will surprize you.

That will beg fifteen times 2160 ; or, 32,400 pounds.

AIR.

How many tons is this?

Divided by 112, it is 289 hundred; and by twenty, to bring the hundreds into tons, it is almost fourteen tons and a half.

It is. But the higher we rise above the surface of the earth, the air becomes thinner and lighter. I have read of travellers who have ascended some of the highest mountains in South America, and who have found it difficult to breathe on their summits. Had they stayed long on those eminences, they would have expired.

The purity of the air is very remarkable, Father. It is, Frank.

It was

necessary that it should be so, for the preservation of health and life. Hence appears the use of winds, and tempests, and storms of thunder and lightning ; these constantly promote its purification. The works of God are not only magnificent, but they are worthy of their adorable Creator, as they are all arranged in infinite wisdom and goodness.

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