Popular Books on Natural Science Part 9

There were two opposite currents of air, which for a time avoided each other, but at length met over our heads. Each current at first pressed on the other with equal force, so that they mutually were brought to a stand-still; this we called a _calm_. But such an equilibrium does not last long, for one current must in the end overcome the other; they whirl through one another, raise the dust in high columns, seize the trees and give them a thorough shaking. The cold current changes the vapor of the warm current into clouds, then into rain. The pouring down rain immediately sets free the heat. At this stage electrical phenomena are witnessed, such as lightnings, claps of thunder, and concussions of the air. And this continues until one current of air has carried the victory over the other; not till then does the weather become quiet again.

Besides these opposing currents of air, which come from the north and south, there are other causes disturbing our weather, viz., the geographical position of our country in regard to the east and west.

A glance on the map reminds us that our continent borders, on the east and west, on that immense waste of water, the ocean. We know now that the air above the water is always saturated with vapors, while the air over the land is comparatively dry. And moist air contains heat, dry air does not; both, however, are continually tending towards equilibrium and wish to exchange temperatures from each other. As our dry air is surrounded on both sides by moist air, it is evident that we must more or less partake of both heat and cold; but it moreover accounts for the happy circ.u.mstance that we have much rain; hence our soil is well watered, and this is a blessing to any country.

CHAPTER XI.

ABOUT THE DIFFICULTY AND POSSIBILITY OF DETERMINING THE WEATHER.

Having now explained the rules referring to the conditions of our weather, and proved that owing to the geographical position of our country, to determine the weather in advance, is difficult, we wish to examine this difficulty a little more closely in pointing out the wrong direction which has. .h.i.therto been pursued in the science of meteorology.

The main difficulty in predicting the weather for any given place consists in this, that a change in the atmosphere need not originate in the place where it occurs. Thus, to-morrow's weather in New York is not a consequence of the condition of the air as it exists there to-day; for the air is continually moving, and, owing to many disturbances, is carried over city and country. We have no sure means of ascertaining whence the wind will come to us to-morrow. All we know is, that from all sides currents of air are moving simultaneously; from the north pole a cold current, from the equator a warm one, from the ocean one saturated with moisture. All these winds are in continual commotion, and have the characteristics of the neighborhood from which they come. If from the state of the weather in New York to-day it were desired to predict the weather there for to morrow, one ought to be able to overlook a s.p.a.ce of about a thousand miles around; in other words, it must first be ascertained what is the state of the atmosphere within about a thousand miles of the city. Besides, there should be known the direction of all the winds within this wide s.p.a.ce, and their speed, and whether they contain much moisture or little. Not without this information could a calculation be made about the velocity with which a change of the weather would take place in New York; what results the meeting of two or more currents of air might call forth; and what kind of weather this might produce there.

Weather, therefore, for the present state of meteorology, is but a subject of investigation into the existing condition of existing phenomena, and not a subject of prediction of coming phenomena. It is true, there are general rules by which a proximate success in predicting may be obtained. If winter begins mild, or, better, if southwest winds and rain prevail till the middle of January, it is very likely that this will be counterbalanced by a northeast wind in the latter part of the winter. The saying, therefore, is correct, "green Christmas and white Easter;" but this rule is by no means infallible, the counteraction may be accelerated by violent storms, or greatly r.e.t.a.r.ded by mild currents of air.

Not before the time that meteorological stations are established throughout the land, and connected by electric telegraphs--a project which to us may seem immense, but to our children will appear very simple and natural--not before that time will a city like New York, for example, receive timely information about the conditions of the currents of air at all the stations. At each of these places the force of the current, its warmth, moisture, and weight will be accurately ascertained by instruments. Then, and then only, we may calculate what currents will meet and where, and what effects the meeting will have. If this be done on Sat.u.r.day, the Sunday papers will be enabled to state precisely whether the church-goers must provide themselves with umbrellas or parasols.

But not for Sunday alone will this be of importance. It will be long after their establishment, that such weather-stations, connected by telegraphs, will prove their real efficiency and blessing; and our descendants, perhaps, will wonder how we could live without an inst.i.tution, which to them will appear as simple and natural as do to us gaslights and railroads, which by our forefathers would have been rejected as idle dreams or works of witchcraft.

CHAPTER XII.

THE FALSE WEATHER-PROPHETS.

We wish to speak here a few words about the false methods, that have hitherto been applied to the investigation and foretelling of the weather.

The weather prophecies of the almanac are a disgrace to our advanced age. Those who still print them deserve that their productions should nowhere find sale. We are not of those who expect everything of the magistrates and their orders; but an example should be set to prevent the publishers from dis.h.i.+ng up to the people such absurdities.

Some of these wily prophets pretend to read their predictions in the course of the planets. For this purpose, they have divided the planets into two cla.s.ses, according to their positions in regard to the earth and sun: 1st, those that produce cold, and 2d, those that produce heat.

By this means they pretend to prophesy how many degrees of heat or cold there will be every day at sunrise or sunset.

When critically a.n.a.lyzed, these prophecies prove to be theoretically and practically nothing but charlatanry.

It is beyond all doubt that the position of the planets is, to state an example, for Boston the same as for the city of Was.h.i.+ngton; if there are any heat or cold-producing planets, they would have the same effect at Boston that they would at Was.h.i.+ngton. But this is not the case. Boston has often cold weather when in Was.h.i.+ngton it is very warm, and _vice versa_. Besides such a heating or cooling influence of planets would be perceivable on every spot of the earth alike which again is not warranted by facts. On the contrary it often happens that when cold winds are pa.s.sing over one part of the country, warm winds are pa.s.sing over another. It is almost certain that cold winters in Europe always accompany warm winters in America; and again, that cold winters in America usually accompany warm ones in Europe. On a closer examination of the facts in the case, we must conclude that, on the whole, weather-prophets take things very easy. Noting the mean heat of each day, and trusting to their good luck, they prophesy one or two degrees above or below. Now, there is no great risk in doing this, and as a matter of course such prophecies are realized one out of two. But at times, almanacs announce an extraordinary increase of cold or heat for a given day, although the situation of the planets does not change suddenly in one day. Then, their predictions very seldom prove to be correct.

In such cases the almanac-makers know how to manage affairs. The country being very large, they send for information to those places where observations on the weather are made. It is almost certain that somewhere in the land their prophesy has come true. Very likely the cold may have increased extraordinarily in the course of a day at New York, Boston, Chicago, Cincinnati, or St. Louis, etc., afterwards the weather-prophets compare their predictions with the results of observation in the various cities, and publish whatever of them are found to have been true.

CHAPTER XIII.

HAS THE MOON INFLUENCE UPON THE WEATHER?

The idea that the moon exercises an influence upon the state of the weather is very general, not only with the people, but also among the better educated. What induces them to entertain it, is not real observation of nature, but a belief which is not without a semblance of truth. If, they say, the moon has enough influence upon our waters to produce tides, it must exercise a still greater influence upon the sea of air surrounding us, and hence it must be of the greatest importance to our weather.

This is, however, an illusion. A long time ago it was proved by Laplace, that tides are caused by the great weight of a liquid. If the ocean were filled with mercury instead of water, the tides would reach a formidable height. Tides, then, do exist in the atmosphere, but in comparison much less than in the water, because the air is so much lighter. It happens that we do not live on the surface of the atmosphere, but in the lowest strata of this airy sea; and in these strata, where the weather manifests itself, the effect of the tides in the upper air is so insignificant, that nothing of it has yet been discovered in spite of most diligent barometer observations.

Learned men have had such a respect for this popular belief, that thorough observations and investigations have been made in order to settle the question.

Those investigations were of three kinds:

1st. What influence with regard to heat and cold has the nearness or remoteness of the moon upon our weather? 2d. What influence has the same upon rain or dryness in the atmosphere? 3d. Has the change of the moon any bearing upon the variability of our weather?

For the reply to these questions, some naturalists have made use of the minutest observations for a period of nearly forty years; during which time the temperature, pressure, and moisture of the air have been measured daily.

These observations have been scrupulously examined; the conclusion arrived at is, that the moon is not quite without influence upon the state of our atmosphere; but this influence is so very small, that it is not brought to bear at all on meteorology.

When the moon is nearest to the earth, it is certainly a little colder than when she is farther off; but the decrease of heat amounts in the average scarcely to one-fifth of a degree, and this is a quant.i.ty entirely imperceptible in our weather. As to rain, it is a little less frequent in the time of the moon's greatest distance from the earth; but this difference, too, is imperceptibly small. In one thousand rain-storms there are four hundred and eighty-eight during the moon's greatest distance, five hundred and twelve during her nearest. As to the pressure of the air, it is during the moon's greater distance somewhat greater than when she is nearer, but this difference is still less than the preceding ones, so much so that a common barometer does not even indicate it.

The most thorough investigations have been made about the influence of the waxing and waning moon upon the weather, because it was on this subject that the greatest illusion prevailed. The result here is likewise, that scarcely any difference exists, and that it is a mere superst.i.tion for people to maintain, that when the moon changes, the weather changes also. The change in the moon, moreover, does not take place all of a sudden, but with great regularity from day to day, from minute to minute; while the weather, especially with us, changes often very abruptly.

It is therefore certain, that in meteorology one has only to observe the earth and her position with regard to the sun, together with the currents of air and the position of land and water. Other phenomena of the atmosphere may be entirely omitted.

PART VII.

OUR ARTICLES OF FOOD.

CHAPTER I.

THE RAPID RENEWAL OF THE BLOOD IS AN ADVANTAGE.

Our articles of food are also called _articles of life_, and very properly so; for that which lives in us is, indeed, nothing but food transformed into ourselves.

According to this, it is very easy to determine what a man must eat in order to live; what kind of food can best maintain his health; what constantly renews his working-power; what compensates for the loss he experiences by emission of breath, perspiration, and excretions.

This easy task many have proposed to themselves. They believe they have solved the problem, if they can but prove that all parts of the human body are fed by the blood; and, the const.i.tuents of the blood being well known, they believe they have done enough, if they designate that food as the most proper for man which contains the const.i.tuent parts of the blood, or which, by digestion, may be changed into blood.

As a general thing this is true; yet it is not sufficient to give the necessary information about the princ.i.p.al articles of our food.

The poor Irishman, who lives almost exclusively on potatoes, has as much blood in his body as the Englishman, whose workmen threaten him with a strike, if they do not earn enough to have a piece of meat and a good gla.s.s of beer for breakfast. The Irishman's blood contains quite the same elements that the Englishman's does, and yet their food is very different; and the Irishman is as justly called "poor," as the Englishman is said to be "well fed."

It is evident that the blood alone does not account for this, nor can it do so. There must be other additional items; and these we shall try to learn before we speak of the different articles of food and their worth.