Various experiments have been tried with animals, and a great deal of information about the best means of feeding the body has been collected.

In order to investigate the effect of the nutritive qualities of food, inquiries have been made especially at military establishments, such as barracks, etc.

CHAPTER IX.

ABOUT NOURISHMENT.

In obedience to the demands of modern science, numerous experiments about nutrition have been made, in regard to digestion as well as to the effects of hunger and of various elements of food.

As to digestion, the most excellent observations were made on men afflicted with a fistula in the abdomen, that is, a wound penetrating to the stomach. By means of this wound, it was ascertained very minutely how long it took to digest food, and what kind of transformation it underwent. From this and other experiments it appeared, that the time for digestion, though varying greatly with the various articles of food, lasts from one and one-half to five and one-half hours. Those most quickly digested are: soft sweet apples, beaten eggs, and cooked brain.

To digest boiled milk, raw eggs, soft sour apples, roasted beef, liver, two hours were required. Cooked spinal marrow, raw cabbage, fresh milk, roasted beef, oysters, soft-boiled eggs, and raw ham, took nearly three hours. Wheat bread, old cheese, potatoes were digested in nearly three and one-half hours; pork, boiled cabbage, lamb's fat, not before five hours.

The experiments about the effects produced by hunger were tried only on animals. The results were that during the state of starvation three-fourths of the blood disappeared; the fat was almost entirely consumed; the flesh disappeared one-half; even the skin diminished one-third, and the bones lost about one-sixth of their weight. The least decrease was found to be in the nerves, a striking proof that nerves possess a great power of self-preservation, provided there be but a minimum of matter to feed them. From numerous experiments the conclusion was drawn, that an adult weighing about one hundred and thirty pounds must die if he were to lose, say fifty pounds, by starvation.

With regard to the effects of the various articles of food, experiments applied to dogs have shown that they can live on bones for a long time; but that they die if fed on sugar only, and when examined after death, no trace of any fat is to be found.

Animals fed on substances that contained no phosphorus and lime became fat; but they died for want of the proper nourishment for their bones.

Animals died also when nourished only with pure alb.u.men or pure caseine.

The most remarkable fact in this connection is, that they perished in the same length of time in which they would have died, _if they had taken no food whatever_.

Experiments tried on man have shown that it is injurious to eat _uniform_ food. A constant change in our food is extremely nourishing and healthy. This is an experience made in prisons and barracks; changes of food are made there every day during the week, so that each day they have a different dinner. Once, a physician in England wished to try the effects of uniform food on himself. He took nothing but bread and water for forty-five days; in consequence of this he decreased eight pounds.

Then he ate for four weeks but bread and sugar, then bread and oil three weeks; but finally he succ.u.mbed under his experiments, and died, after having experimented thus for eight months.

We must not, therefore, call it daintiness when we feel an appet.i.te for more variety of food, or if we soon get tired of uniform meals: a constant change in this respect is necessary. Experiments have shown that rabbits continue their health, if alternately they receive one day potatoes, the next day barley; but if they receive exclusively potatoes or barley, they soon die.

In conclusion, we will mention a few articles of food and their qualities. Among grains, wheat is known to be the most nutritive, and wheat bread and meat taken together is always good, wholesome food. Rice produces fat, but if taken by itself, it is not worth much, since it is nourishing only if eaten with b.u.t.ter, or fat, and a little meat. Potato is a cheap, and yet an expensive food; for it contains very little nutriment. In order to be of benefit it must be eaten in great quant.i.ty; besides, it is necessary to season it with salt, b.u.t.ter, or fat, as otherwise it would be totally useless. A good diet is peas, beans, and lentils; but their hulls are indigestible, and must be removed.

In general, beverages are not counted among articles of food; and kitchen-salt is commonly believed to be but a matter of taste; but this is a great mistake. Coffee and tea, too, are nourishing in their way; good beer is equal to half a dinner, and as to salt, a frequent relish of the same is an excellent means of nutrition.

Cheap coffee, cheap beer, and cheap salt are therefore a great benefit to the people.

PART IV.

LIGHT AND DISTANCE.

CHAPTER I.

SOMETHING ABOUT ILLUMINATION.

From time to time we hear of plans to illuminate whole cities by a great light from a single point. The credulity of the newspaper public about affairs belonging to Physics is so great, that we are not surprised if such plans are spoken of as practicable; though, indeed, one needs but cast a glance of reflection on them, to be at once convinced of their impracticability.

The impracticability does not consist so much in this, that no such intense light can be made artificially, as in the circ.u.mstance that the illuminating power of light decreases enormously as we recede from it.

In order to explain this to our readers, let us suppose that on some high point in New York city, say Trinity-church steeple, an intensely brilliant light be placed, as bright as can be produced by gases or electricity. We shall see, presently, how the remoter streets in New York would be illuminated.

For the sake of clearness, let us imagine for a moment, that at a square's distance from Trinity church there is a street, intersecting Broadway at right angles. We will call it "A" street. At a square's distance from "A" street let us imagine another street running parallel to it, which we will call "B" street; and again, at a square's distance, a street parallel to "B" street, called "C" street; thus let us imagine seven streets in all--from "A" to "G"--running parallel, each at a square's distance from the other, and intersecting Broadway at right angles. Besides this, let us suppose there is a street called "X"

street, running parallel with Broadway and at a square's distance from it; then we shall have seven squares, which are to be illuminated by one great light.

It is well known that light decreases in intensity the further we recede from it; but this intensity decreases in a peculiar proportion. In order to understand this proportion we must pause a moment, for it is something not easily comprehended. We hope, however, to present it in such a shape, that the attentive reader will find no difficulty in grasping a great law of nature, which, moreover, is of the greatest moment for a mult.i.tude of cases.

Physics teach us, by calculation and experiments, the following:

If a light illuminates a certain s.p.a.ce, its intensity at twice the distance is not twice as feeble, but two times two, equal four times, as feeble. At three times the distance it does not shine three times as feeble, but three times three, that is nine times. In scientific language this is expressed thus: "The intensity of light decreases in the ratio of the square of the distance from its source."

Let us now try to apply this to our example.

We will take it for granted that the great light on Trinity steeple shines so bright, that one is just able to read these pages at a square's distance, viz., on "A" street.

On "B" street it will be much darker than on "A" street; it will be precisely four times darker, because "B" street is twice the distance from Trinity church, and 2 2 = 4. Hence, if we wish to read this on "B" street, our letters must cover four times the s.p.a.ce they do now.

"C" street is three times as far from the light as "A" street; hence it will be nine times darker there, for 3 3 = 9. This page in order to be readable there, would then have to cover nine times the s.p.a.ce it occupies now.

The next street, being four times as remote from the light as "A"

street, our letters, according to the rule given above, would have to cover sixteen times the present s.p.a.ce, for it is sixteen times darker there than on "A" street.

"E" street, which lies at five times the distance from the light, will be twenty-five times darker, for 5 5 = 25. "F" street, which is six times the distance, we shall find thirty-six times darker; and, lastly, "G" street, seven times the distance from the light, will be forty-nine times darker than "A" street, because 7 7 = 49. The letters of a piece of writing, in order to be legible there, must cover forty-nine times the surface that our letters cover now.

But the reader will exclaim: "This evil can be remedied. We need but place forty-nine lights on Trinity steeple; there will then be sufficient light on "G" street for any newspaper to be read." Our friend will easily perceive, however, that it is more judicious to distribute forty-nine lights in different places on Broadway, than to put them all on one spot.

This is sufficient to convince any one that we may be able to illuminate large public places with _one_ light, but not the streets of a city, and still less whole cities.

CHAPTER II.

ILLUMINATION OF THE PLANETS BY THE SUN.

It was demonstrated above, that it is impossible to illuminate large distances by a single light. Yet we must acknowledge that nature herself does this, and that the sun is the only light which shines throughout the solar system; for the light which is seen in the planets is but light received and reflected from the sun.

This is sufficient reason for us to believe, that there are not on every planet creatures as we see them on our earth; but that, on the contrary, each celestial body may be inhabited by creatures organized according to the distance of the planet from the sun; that is, adapted to the degree of light produced there by the sun.

For the natural sciences teach us, that solar light is subject to the same laws as our artificial light: it decreases as the distance increases. The planets more remote from the sun are illuminated less than those nearer to it. The ratio in which this light decreases, is precisely the same as that of the terrestrial light ill.u.s.trated above, viz., according to the square of the distance. In other words, when the distance is double, the intensity of the light is one-fourth as great; when three times, one-ninth as great; when four times more remote, one-sixteenth as strong, etc.; in short, at every distance as much weaker as the distance multiplied by itself.

Presently we shall see that the planets are illuminated in inverse proportion to their distance from the sun. From this alone we come to the conclusion, that on every planet the living beings must necessarily be differently const.i.tuted.

The name of the planet nearest to the sun is Mercury. It is about two and a half times nearer to the sun than our earth, therefore it receives nearly seven times as much light. We can scarcely conceive such an intensity of light and all the consequences resulting from it. If instead of one sun we should happen to have three, there is no doubt that we should go blind; but seven suns, that is, seven times the light of our brightest days, we could not endure, even if our eyes were closed; the more so, as our eyelids, even when firmly closed, do not protect us from the sun's light entirely. This is a proof of our a.s.sertion, that the living beings on the planet Mercury must be differently organized from us.