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Popular Science Monthly/Volume 29/August 1886/The Prediction of Natural Phenomena

< Popular Science Monthly‎ | Volume 29‎ | August 1886


ALTHOUGH those times have gone by which oracles and soothsayers played an important part, yet even at the present day prophets are to be found almost everywhere. We will not speak here of politicians, of those that predict peace and war, nor of speculators and the so-called reformers, with their predictions in the domain of commerce and industry. We shall confine ourselves to the discussion of natural phenomena—not alone to those that are grand and striking, but shall in preference turn to the common occurrences of everyday life.

"What weather are we to expect within the next few days?" Only put the question, and a hundred answers will be volunteered. The curing of all diseases is often predicted by quacks and patent-medicine men with a degree of assurance scarcely to be believed. "This remedy never fails," is the superfluous winding-up of many an advertisement of their nostrums, and thousands of credulous people daily fill the pockets of these charlatans.

A considerable number of those persons who do not permit themselves to be thus caught err in the opposite direction—that is to say, they regard all predictions with mistrust. For instance, they attach but little importance to any of the attainments of medical science; they doubt the usefulness of meteorological stations, etc. And yet even skeptics like these must acknowledge that numerous astronomical predictions come true with a degree of precision and accuracy that must astonish every one.

What prophecies, then, are to be believed? The predictions of science? Alas! how many supposed scientific predictions have proved to be mere delusions! The word "science" will not answer in this connection. Is there, then, no standard by which the value of predictions of natural phenomena may be gauged or measured?

A standard exists, and may be determined by an acquaintance with the elements of inductive logic, and with the most important teachings of natural science. Considering the wide-spread interest that attaches to this question, it will be worth while to study the subject a little more closely.

Almost every prediction requires some statement admitted to be universally valid, from which it may be deduced. If one desires to know how probable a prediction is, it will be well to test it by the following questions: Does the prediction rest on simple enumeration? Is it based on the general law of causation? Does it presuppose the acceptance of any theory?

Predictions and generalizations based on Bacon's system of induction and simple enumeration are the most common and best known; they are based on the observation of Nature without experiment. They take the facts as they are, and merely enumerate. This method governed the whole world before the development of natural science. Even to-day it is made the basis of prediction by all who are not familiar with the method of experimental investigation. In this category must be classed the sayings of country people purporting to foretell the weather. If a farmer who places faith in such sayings be asked upon what grounds his belief is founded, he will probably answer, "For so and so many years I have watched the weather, and have always known these rules to come true." At the best, his observations will have been none too accurate; and as to any actual relation between prediction and fulfillment, of course that is out of the question.

Even nowadays many families cling to the superstition that thirteen people should not be seated together at table, because it is a sign that one of the number will die in the coming year. Should any question be asked as to the reasons on which such a fear might be founded, a great many incidents will undoubtedly be related, instances where thirteen dined together, and death claimed a victim from among the number before the year had passed. The many occasions where thirteen have dined together and no one of the number has died within the time prescribed (and how often does this not occur in inns and other public places, and no one gives the matter a thought!), these instances are of course completely ignored. A patient, who may have consulted several physicians without experiencing relief, finally turns to one of the many patent-medicines advertised in the papers. After a time he feels better; perhaps the improvement is but temporary, as is so often the case in troubles of long standing, but then, oftentimes urged thereto by the proprietors of the wonderful medicine, he writes a letter of thanks, and anon the papers will herald the announcement, "Sure cure to all unfortunates by the famous cure-all, ——," and then comes some pompous name. Other patients think a great deal of the so-called "sympathetic" cures. When the moon is on the wane they go to a graveyard, taking care to speak to no one on the way, or they throw barley-grains over their head backward into the water, meantime muttering some incantation. If the believers in these cures be questioned as to how they can place faith in such wondrous arts, they will refer to certain instances where such means have been successfully employed; but of course they can trace absolutely no connection whatever between the remedy and its supposed effects.

Prophecies of a similar kind, that do not, however, exactly refer to natural phenomena, can only be mentioned here. Thus, a northern light or a comet is said to be the forerunner of war. The relative position of certain stars at the birth of a child is, by the superstitious, said to bode good or evil. If a new piece of work be commenced while the moon is on the wane, or on a Friday, the undertaking is doomed to fail. The belief in good and evil omens has survived thousands of years, and has come down to the present day; in fact, the influence which this belief has on the mind can only be shaken off by calm reasoning and self-training. Many other instances of superstition, still in vogue in our enlightened times, might readily be given.

All of these are false conclusions derived in the same manner: post hoc, ergo propter hoc (after it, therefore because of it). A careful comparison of different cases is not undertaken, no close scrutiny or investigation is attempted, no distinction made between essential and non-essential conditions. In each case a general assertion is based on a few separate, consecutive facts; the relation between cause and effect can not be proved in any instance. In fact, if we except the example of quack-medicines cited, in all other cases, even the most vivid imagination will fail to cast a bridge—be it ever so frail—over the chasm that separates what has preceded from the seeming effect. In short, many prophecies that can be found and met with every day among the people, in newspaper advertisements, etc., are replete with error, and wholly unreliable. It is, then, not surprising that one comes to regard all predictions skeptically; in fact, one is entirely justified in looking upon at least nine tenths of them with suspicion.

The true observer will not rest content with the mere word "experiment," a term so universally used. If one comes to look into matters closely, it will nearly always be found to refer to mere enumeration. Rarely has a word been more misused than this one, "experiment." Science has found a more adequate expression, and terms it "induction." Induction is the means of discovering and proving general propositions. This simple definition should be remembered.

The best-known form of induction is Bacon's method by simple enumeration. Can this method be successfully applied to formulate predictions? Many scholars consider this way of going to work entirely useless for the ascertaining of truths. "Of what use can it be," they say, "to know that a certain phenomenon has taken place a hundred times? Does that afford any guarantee that it must take place again? Or, even granting that it may happen once more, can not the time come when it will not occur?"

Hence, induction by simple enumeration does not seem to be adapted to the finding of general truths, such as science demands, and in consequence does not seem serviceable as a means of securing definite predictions. In fact, induction applied without the necessary caution is the most crude and deceptive means of arriving at general truths, and gives rise to innumerable false conclusions; and yet we owe to this inadequate method some important empirical generalizations. In many parts of Europe the saying is common, "A western wind brings rain," and it is undeniable that there is a certain connection between rain-storms and a wind from the west. Occasionally, however, rain will put in an appearance from whatever quarter the wind may be blowing. But, as rain is experienced particularly often during westerly winds, the statement above—"a western wind brings rain"—may, with some slight reserve, be permissible.

Almost every one owns a barometer. If, in the summer-time, some little excursion is planned, the mercury in the tube is watched with anxious eye to see whether it will rise, for this is generally regarded as predicting clear and dry weather, whereas the sinking of the mercury points to rain and storm. Until quite recently the true relation between these phenomena was not known to science, and yet it could be safely assumed that there was, in some way, a connection between them. Thus, Otto von Guericke, the inventor of the air-pump, in the year 1660 correctly predicted a storm from a considerable depression that he observed in the water-column of his immense barometer, which measured nineteen Magdeburg ells in length.

If we look back for a moment on these predictions in the field of natural science, we must admit that they can not lay claim to any great degree of accuracy. In Europe, as well as elsewhere, a westerly wind is often accompanied by fair weather; and sometimes it will rain, although the mercury has risen in the barometer.

Predictions like these may hence be made, but with a certain amount of reserve. Some of them, however, are predictions of a superior order—to be discussed hereafter—as in many of them the accompanying conditions are studied, and hypotheses as to the phenomena observed are formulated and discussed in connection with others. The generalizations considered thus far may only be looked upon as probable; there are, however, instances in which the probability can be more fully depended on, although, in these too, the simple method of enumeration is employed.

A case where the probability of the prediction borders on certainty is found in chemistry in enumerating the properties of chemically pure substances. If we say, "All globules of mercury have a grayish-white color, a metallic luster, are opaque," etc., these are assertions true without exception as far as mercury in the perfectly pure state is concerned. If we are dealing with a substance that is chemically pure, we can predict with certainty that it is endowed with certain properties. In fact, we may state it as a natural law that, under all circumstances, substances which have been recognized as identical by the comparison of a series of properties will exhibit other series of like properties. We will call this the law of coexistence of like properties, or, to be brief, the law of coexistence.

The counterpart of this is the law of universal causation. This law, so important a one for predictions, may be thus expressed: under exactly the same conditions, the same natural phenomena will always take place.

This law is at the present time recognized by all philosophers. There is, however, a dispute as to whether it is true a priori, or whether it can only be proved by experience. John Stuart Mill justly insists that the latter is the case. The correctness of this law is rendered evident through simple induction by means of mere enumeration. It was only a clear understanding of this law that brought about exact repetition of scientific experiments, and made possible positive predictions of the phenomena that would follow.

Another class of predictions and generalizations is based on the law of universal causation, or Mill's induction. It was about the middle of the seventeenth century that the fundamental principle of the law of universal causation began to take root among the natural scientists, as the impression gained ground that in nature like conditions necessitate the taking place of like phenomena. Since then, this fundamental principle has gradually come to be general property of all sciences. It has even penetrated into many classes of the people, into the workshop of the mechanic, into the hut of the glass-blower. It is, however, undoubtedly true that with many persons the idea is not clearly brought to consciousness, that thousands of mechanics, miners, etc., act in accordance with it, without being able to express in words what they seem to feel instinctively. If in their work some attempt fails, if the matter turn out differently from what they had expected, nowadays, they will hardly ascribe the failure to some evil spirit who seeks to mock them, but the eyes of the common workman oftentimes will more quickly discover the fault in his appliances and apparatus, than the "evil-eye" of the superintendent.

The essence of Mill's teaching is the empirical deduction of the conception of causes. He has practically evolved this from the law of causation. When an event takes place on a certain combination of conditions, and if this event no longer results when one of these conditions is omitted, then this condition is an essential one, a part of the cause. What, then, is the cause of a natural phenomenon? It is the sum of the essential conditions, in consequence upon which the phenomenon invariably follows. Now, it is evident that, if the cause of a natural phenomenon be known, and if this cause occur in any given case, then the effect can be predicted with certainty. This gives us a clearer insight into the theatrum mundi, so that in many instances we may know on the rising of the curtain what must come.

If a chemist announces the existence and the properties of a newly discovered substance, for instance, of a new coloring-matter, and we place faith in the accuracy of his work, then we feel convinced that this substance will always be again found whenever the same conditions are brought about, although the induction in this case may be based on only a few observations, or may rest perhaps on a single but well-observed instance. An experienced photographer knows that his work will be successful, provided he carries out with care certain directions that have proved efficient.

If new gas-works or telephone-stations are to be set up in a town, it is desirable that one proceed in the same manner as has been done in the erecting of the best of similar establishments elsewhere. If this be done, then good gas-light, etc., may be guaranteed.

At this place should also be mentioned the repetition of laboratory experiments on a large scale. In such cases the results attained may astound the lookers-on, especially if nothing of the kind has been previously known, but the originator may calmly await developments after he has once made sure of the result on a small scale. It was but a short time ago that the reefs at Hell-Gate were blasted. This grand act was brought about ultimately by the pressure of a child's finger on an electric knob, and the event took place precisely as had been expected.

Of late the correct application of the law of causation has become of great importance in agricultural chemistry. It is a well-known fact that plants need for their nourishment not only water, warmth, and light, but also a quantity of certain salts contained in the soil. When wood or other vegetable fiber is burned, ashes remain; these represent the salts that the plant has abstracted from the ground during its life. Bearing this in mind, the ashes of the cereals, of clover, and other plants used for feeding purposes have been examined—the ashes of the seeds as well as of the leaves and stalks.

In connection with these investigations the so-called water-cultures of some plants were undertaken. These consist in raising plants in flasks with water, adding to this, in some cases, certain salts found in the ashes of the plant, and in other cases withholding some of these salts, in order to study their respective influence. In this manner the effect of the different constituents of the ash has been traced, and in this way the means have been found, not only of securing the proper nutriment for the products of the field and the flowers of our gardens, but of raising crops of a desired quality—in fact, of causing crops to grow on soil that would previously not bear at all. An effectual guard has thus been found against exhaustion of the soil and all its consequences.

The examples cited will suffice to show that considerable importance attaches to this class of predictions and generalizations, based on the law of causation. Generally speaking, these are the most reliable predictions that can be made. To what extent these are worth believing in depends, of course, on the amount of care with which the conditions that affect them have been observed, also on the extent to which they may be varied, and on the more or less accurate knowledge possessed as to the effects which are produced by these conditions.

Other predictions and generalizations are based on theories and hypotheses. Unfortunately, Mill's induction and the ascertainment of cause by eliminating the non-essential conditions will no longer suffice when the natural phenomena to be examined are too complex, or when several important conditions can not be subjected to observation; this may be owing to various reasons, such as excessive distance, extreme minuteness, insufficient acquaintance with the matter, etc. One has not far to seek for instances of this kind, for a great number of natural phenomena belong wholly or in part to this division. We may here refer to the complex processes which take place in the human system, to many phases of animal and plant life, to the evolution of the crust of our globe, to the problems presented by the starry heavens.

When observation and direct investigation do not suffice for the finding out of the cause, the investigator turns for aid to theory or hypothesis. These differ only in degree, and we will consider them both as theory in a wider sense. Our main interest here centers in the predictions of a theory; these afford the standard by which the value of a theory may be determined—its merits correctly judged. The larger the number of successful predictions under varying conditions, made by means of a theory, the higher will such a theory deservedly rank in our estimation.

In chemistry, the modern theory of the science well serves to illustrate this point; in physical geography, the tides furnish a striking example. It seems remarkable that Pythias already divined a certain relation between the phenomena presented by the tides and the moon. In the middle ages, however, this view of the case was again obscured by wrong hypotheses. The basis for a clearer understanding of the periodical changes of the sea's surface was presented by Kepler in his statement that, if the earth should suddenly cease to attract the waters upon it, these would immediately strive toward the moon. Why the sea should also rise on that side of the globe not facing the moon was satisfactorily explained by Newton. When the dependence of the tides on the combined force of attraction of all the celestial bodies concerned had been established, much still remained to be done in the last century in the way of accounting for and settling fine points and details. In 1740 the Paris Academy presented as subject for a prize essay the problem of a mathematical theory of the tide phenomena; in consequence, such a theory was partly developed by several competitors. But it remained for Laplace to bring mathematical calculation into harmony with the theory, by applying it to the prediction of the actual movements of the waters. Nowadays many calendars, especially those of seaports, state the exact time of the setting in of ebb and flood tide, calculated a year in advance.

The most striking proofs of the coming true of predictions based on theoretical speculation are undoubtedly furnished by astronomy. The views of Ptolemy already permitted a limited series of predictions, but the faults of his system became more and more apparent in the course of time. A remedy for this was sought in complicated extensions of his teachings; this, however, only made matters so much worse, without explaining the facts. King Alfonso X of Castile is reported to have said to his astronomers that, if the arrangement of the universe had fallen to his lot, he would have made things much more simple. All of these difficulties were suddenly removed by Copernicus. The course of the planets now no longer appeared a cause for great perplexity, but admitted of a simple explanation and resolved itself into one grand harmony. Then, after Kepler had discovered the three laws that bear his name and which mark a new era in the science, the mathematical part of the work was brought to an end by Newton's discovery of the law of gravitation.

Eclipses of the sun and moon always attract general attention. On such occasions it is not only the phenomena themselves that call for our admiration, but mainly the art which makes possible the prediction of these events to the hour, the minute, ay, the second; by means of which one may know in advance whether the eclipse will be total, partial, or annular, what part of the sun or the moon will be first covered, how long the phenomenon will last, and from what parts of the world the eclipse will be visible.

If a prediction rest on a hypothesis prepared ad hoc, no matter how ingenious it may be, our doubts and our mistrust are justified. In such a case we have the right to ask for confirmation, and to demand that the hypothesis shall be extended into a theory by its sequence, and that this sequence shall stand in accordance with the actual facts. If, however, a prediction is based on a theory which approaches in thoroughness and in extensive confirmation the cases we have cited as examples, and furthermore, if the separate instance be deduced in a strictly logical manner, then the prediction is worthy of our confidence. As most systematic classifications are of value only in affording a general view of the ground, without being able to embrace all cases, so, too, in our classification, we meet with instances of transition and combination.

Of this, examples are to be found in all the sciences, but notably so in medicine, geology, and meteorology. The predictions in medicine to a great extent form transitions between the first and the second class; that is to say, they are based in part on Bacon's, in part on Mill's system of induction. Thus, of late, the theory of bacteria has come to be of great importance. This theory is of recent origin, but has deservedly many champions, and offers an insight into new ways, which medicine, in combination with natural science, must explore in order to obtain valuable results. Based on these views, which would designate certain bacteria as carriers of certain diseases, new precautionary measures have been adopted, which are to serve as a guard against the phantoms of disease; and in many places these measures have already proved of great value. The meteorology of to-day is in a state of development similar to that of medicine. Within the recent past, this science too has made wonderful progress, and is rich in promise for the near future. The meteorological predictions prove of great service to the agricultural interests in the United States. The whole system is excellently organized and very extensive; the official publications embrace the "probabilities" and the so-called "weather-maps."

While meteorology is concerned with the rapid changes that take place in the atmosphere, the science of geology is devoted chiefly to the study of the slow changes ever going on in the crust of our globe. If the geological formation of a district be but known in its essential features, a geologist is often able to predict the finding of coal-beds, ore-deposits, etc., basing his prognostication on the occurrence of certain fossils, the order in which the strata are placed, analogous formations in other districts, and so on.

Finally, we must just refer to one class of—shall we say predictions?—that are based on illusions. To cite but one example of this type, Nostradamus predicted that in this year, 1886, the world would come to an end, because Good Friday this year happens on St. George's day, and Easter coincides with St. Mark's day—i. e., the 25th of April, the very latest date on which Easter can happen. At the present time a prophecy of this kind is only commented on as a matter of curiosity, whereas the year 1000, for which the coming-to-an-end of the world had also been predicted, witnessed a general preparation for the event.


  1. Translated and condensed from Virchow and Holtzendorffer's "Sammlung gemeinverstandlicher wissenschaftlicher Vortrage" ("Collection of Popular Scientific Lectures").