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laden with the treasures of foreign lands; and then, when they ebb, they bear out those which are laden for foreign countries.

But how is it, Father, that the waters thus ebb and flow?

It is from the attraction of the sun and moon; but principally from the influence of the moon, as she is so much nearer to the earth than the sun. The tides occur about twelve hours and three-quarters from each other. The moon has the greatest attractive influence when on the meridian.

But you told Charles, Father, the other day, that it was not high water till three hours after the moon had passed the meridian.

I did; and it is so. This arises from that property of matter which I named to you, by which it would continue in the same state.

Will you explain the Spring and Neap tides to me, Father?

I will, Frank; the spring tides happen at the times of the new and full moon: at the new moon, the sun and the moon attract in the same direction; and when it is full moon, the influence of the sun is but little in opposition to that of the moon. The Neap tides, are at the first and last quarters of the moon; then the sun raises the water, where the moon depresses it; and depresses it where the moon raises it. The tides are highest, on the middle of the earth's surface; because the attraction

of the sun and moon are principally on this part of the globe. What a sublime idea does a Sacred Writer give us of the blessed God, when he says, that he holdeth the mighty waters in the hollow of his hand!

But what is most delightful, Father, is, that this great Being will become our Father!

It is; seek, my dear Frank, this first of blessings it is better than life.

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, ourns with great brilliancy; if put into nitrogen, it is as soon extinguished as if put into water; an animal put into it, die 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 aeg. And we can ascertain the pressure of the ar, 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 pounds and

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