METEOROLOGY.—I.

SCOPE OF THE SCIENCE - AERIAL PHENOMENA - WINDS ISOBAROMETRIC LINES-STORMS-MEAN TEMPERATUREISOTHERMAL LINES -EFFECTS OF LOCAL CAUSES ON CLIMATE.

The trades, monsoons, and other periodical winds, have already been explained in treating of Pneumatics. Near the equator, and running almost parallel to it, is a belt some 4° or 5o in breadth, known as the Region of Calms. The position of this varies with that of the sun, and the whole region is characterised by very heavy rains and frequent thunderstorms.

As the winds are mainly produced by variations in the barometric pressure, great light is often thrown on their phenomena by observing the different pressure at neighbouring places. Maps are now drawn with isobarometric lines marked on them; that is, lines passing through those places where the mean much may be learnt from them.

Owing to the very many causes that are at work, there is great difficulty in tracing out all the laws by which these phenomena are governed; and though many weather prognostics have long passed into current proverbs, it is only recently that true progress has been made in the study of the science. In early times, when the occupations of most men kept them much in the open air, and consequently exposed to all the vicissitudes of the weather, they would naturally make various observations, which would enable them to foretell to a limited extent the probable changes. These observations were handed down from generation to generation; but were far too vague and general to serve in any way as the foundation of a science.

In modern times, however, various instruments have been devised for ascertaining accurately the pressure, the temperature, the humidity, and other important matters in connection with atmospheric changes; and now, by means of the barometer, thermometer, and similar instruments, constant records are being kept, in different places, of all these changes.

In a science like Meteorology, it is only by the careful examination of long-continued records of this kind that true progress can be made. The first thing required is to observe the phenomena accurately, and we must endeavour to explain and account for them. To start hypotheses first, and then endeavour to reconcile observations with them, is a mistake.

So numerous and varied are the phenomena with which we have to deal, that it is somewhat difficult to classify them. For the sake of convenience we may divide them into aerial, aqueous, and optical phenomena. It must not, however, be supposed that these classes are indicative of fundamental differences.

The chief physical properties of the air have already been referred to in our lessons on Pneumatics and Chemistry, to which, accordingly, we must refer the student. In this aerial ocean we meet with regular tides, but currents produced by other causes are far more common and important.

These currents in the air are known as the winds, and they usually arise either from a change in temperature, or in the amount of watery vapour it holds in solution. The direction of the wind is always indicated by the point of the compass, from which it appears to come; and as the weather and climate of any place are greatly affected by the prevailing direction, considerable attention has been directed to the subject, and records are kept in many places showing the direction and intensity of the wind at stated times every day. From such registers it appears that in this country S. W. winds are the most prevalent, since they blow on the average 225 days out of every 1,000. We find, too, that westerly winds are more common than easterly, in the proportion of about 220 to 145.

The prevailing character of any wind depends chiefly upon the countries over which it passes. With us, a west wind is usually moist and mild, having swept over the Atlantic Ocean, and thus become partly charged with vapour and warmed. So, too, in the south of Europe, especially in places where the Mediterranean is narrow, a south wind is very hot and dry, from having swept over the arid deserts of Africa. In Italy this is especially noticeable, and this wind is there distinguished as the "Sirocco." A similar wind, but more injurious in its effects, is very prevalent in the desert regions of Arabia and Syria, and is known as the Simoom." This is frequently spoken of as poisonous. It appears, however, that it is merely a very hot, dry wind, completely charged with fine dust. Everything exposed to its influence becomes rapidly dried up; the skin is parched and dry; a general languor comes over everything; and if the traveller is unable to find a place of shelter, he not unfrequently perishes.

The climate of most places is greatly influenced by local peculiarities, as will be more fully explained, and hence these must be taken into account. In tropical regions, however, these local influences are almost overpowered by the great and regular currents which prevail, and therefore they interfere far less than they do in more temperate climes.

The investigation of the laws governing storms and their movements is one of the most important but most difficult questions in Meteorology. The great destructive power which they possess, and the extent to which they may be guarded against when expected, show the importance of this inquiry. What is most needed for this purpose is a complete set of simultaneous observations made during the prevalence of any storm; and, as observers are now stationed in different parts of Europe, these observations have frequently been obtained.

The best method of examining them is to lay down on a map isobarometric lines showing the pressure during the storm in different places, since this appears to be the most important item in the inquiry. By charts of this kind it is found that the centre of the storm is marked by a region of unusually low pressure, the barometer often standing considerably below 29 inches. The barometric lines, too, are usually circular or elliptical. Occasionally, these curves are very irregular, but this often arises from two or three storms which have parted from the original one, and sometimes re-unite with it.

As a storm dies out, the central depression becomes much less, and occupies a more limited area. The direction in which storms travel in Europe is usually from S.W. or W.S.W., and is more or less circular. The rate at which they move varies considerably, but is usually about eighteen or twenty miles an hour, though it has been known to be twice as great.

Since the west of Ireland is some 450 miles from the east coast of England, a storm appearing in the former locality may at once be announced to eastern seaports, and thus nearly twenty-four hours' notice of its approach may be gained. In order, however, to be of much service, these notices must be transmitted at frequent intervals. If only daily signals are sent, the storm may outstrip them. In calm weather, one report would, of course, suffice, but in unsettled weather they should be much more frequent.

The direction of the wind during a storm is not directly towards the point of least pressure, but usually to some point a little to the right of it, so that the wind flows in a spiral direction round the area of low pressure. The force at any place is usually proportional to the difference in the pressures at the places between which it is situated.

In tropical regions storms are much more frequent, and are there preceded by a very sudden and remarkable fall in the barometer. During a storm which raged at Guadaloupe on the 6th of September, 1865, the mercury fell 1693 in. in one hour and ten minutes. This sudden fall relieves the ocean of a large portion of its pressure, and hence the water is often raised to a considerable height by the greater pressure all around. To this cause must be attributed those storm-waves which frequently accompany tropical hurricanes, and often cause a great loss of life and property. The rotating character of these storms is very clearly seen, and when the centre is over any place, the clouds in the zenith are frequently seen to be revolving rapidly.

In the tropics the movements of the barometer are very regular indeed, the daily variation being most distinctly observed. Any deviation from this at once indicates a disturbance of the atmosphere in the locality, and affords a sure method of foretelling a storm. An isolated observer may, in fact, easily ascertain their approach, and give warning of it.

In our latitudes the irregular variations of the barometer are

so much greater than the regular ones, that this cannot be done by a single observer. By means, however, of a staff of observers scattered over Western Europe, and able to communicate by telegraph, most storms can be predicted, and notice be sent to various ports, so as to warn sailors of their approach.

A system of this kind was commenced and carried out by the late Admiral Fitzroy up to the end of 1866, and though many errors crept in at first, the majority of the warnings were correct, and the per-centage of these steadily increased. Those places on or near the west coast were, of course, unfavourably situated for receiving the warnings, since the storms usually commenced in that quarter; and, in the case of a few storms not foretold, the reason usually was that a constant watch was not kept at Valentia, in the west of Ireland. The great difficulty in this matter is not the foretelling of the storm itself, but the ascertaining in what direction it is travelling, and thus only sending the warnings to those places where it is likely to be felt. It is certainly a matter of regret that they have been discontinued, and to be hoped that they may ere long be re-established on a better footing. The amount saved in loss of shipping would much more than defray their cost.

A very important point in connection with the climate of any place is the mean temperature of the air. This is ascertained by reading the temperature indicated by a thermometer every hour, and taking the mean of the twenty-four observations thus made in the day. If we take the mean temperature at any two hours of the same name, we arrive at a result differing only by a fraction of a degree. This is most accurate if we take the mean of 9 a.m. and 9 p.m., or of 10 a.m. and 10 p.m. The two former are usually chosen as being most convenient; when practicable, four equidistant observations should be made. Several years' observations must be compared to obtain the

true mean.

upon the mean temperature, for the range of temperature-that is the difference between the maximum and minimum readings exerts a very important influence on it. Thus, for instance, Madrid, and Mentone on the Gulf of Genoa, were observed to have the same mean temperature, viz. 72.8° during September, 1865. The climates were, however, widely different, for, in the case of the former, the means of the hottest and the coldest periods of each day were 86.2°, and 59.5° respectively. Those at the latter place were 77.6° and 68-0° only. The importance of observing this point is further shown by the fact that the rate of mortality is found to vary with the range.

An insular climate usually has this range very limited in extent. The specific heat of water being very high, it varies but little in temperature through the year, and the changes that do occur in it are very gradual. The result is that in localities close to the sea, the hot winds are cooled and the cold ones warmed by passing over the water, and thus the temperature is much more uniform than in situationsfurther inland. The following list shows the difference between the extreme temperatures recorded at a few places :

In some localities the range is even greater than any of these. By taking a long series of observations at different places, the mean temperature of each is ascertained, and lines can then be drawn on a map, passing through those places which have the same mean annual temperature. These lines are called isothermal lines. They were first noticed by Humboldt, and serve to show the general distribution of temperature. On the sea they are almost parallel, but on the land they are somewhat irregular, as elevation above the sea-level greatly influences the temperature.

Another important thing to notice is the extreme temperatures registered during the day. These are very easily noted, as thermometers are now made which register the maximum and minimum temperature. The maximum thermometer usually employed is a mercurial one, with a small steel index moving in the tube above the column. As the mercury expands, it drives this before it, and leaves it at the highest point attained, the mercury not attracting the steel enough to draw it back again.

The line showing the highest mean temperature, or, as it is usually called, the warmth equator, is almost entirely in the northern hemisphere, attaining on the eastern side of the African desert the latitude of 17° N. The mean temperature of the place is 87° or 88°. The fact of this isothermal being thus situated is owing to the great preponderance of the land in the northern hemisphere over that in the southern, the surface of the land absorbing the heat more readily than that of the sea.

In the minimum thermometer (Fig. 1), the tube is usually filled with spirit, and a similar index is placed in it. As the spirit contracts, it drags this index with it; but when the temperature rises again, the spirit passes it, and it is thus left lying at the point indicating the lowest temperature reached. Both these thermometers are set by bringing the index to the top of the column, either by inclining the instrument, or by means of a small magnet. They are read off and set at a regular time each day, the highest and lowest temperature being entered in a book provided for the purpose. If we take the mean of these two readings, we shall find that it differs very slightly from the mean daily temperature obtained as already explained.

When daily records of temperature are kept, great care is required to ensure that the thermometers employed are correctly graduated and properly placed. Many common thermometers, when compared with a standard one, are found to be very inaccurate. The instrument employed should therefore be carefully verified; and most good instruments are now sent to Kew Observatory for that purpose before they are sold. To ensure accurate readings, the instrument should be shielded from the direct or reflected rays of the sun, but at the same time be exposed to a free current of air. The minimum thermometer should also be placed at a distance of four feet above the surface of the ground, as the readings are otherwise considerably affected by radiation from the earth. In a spirit thermometer there is frequently a tendency for some of the spirit to condense in the upper part of the tube, and thus to render all the readings too low by this amount. Many of the very low readings which are sometimes noticed by newspaper correspondents may be accounted for in this way. The thermometer should therefore be occasionally examined and compared with another to guard against errors of this kind.

The climate of any place, however, does not depend alone

Besides the general causes which account for temperature, there are local ones which exert a great influence on that of any particular place. The most important of these are the altitude above the sea-level, the direction of the prevailing winds, and the proximity of the sea.

In many places, the climate of which is remarkably salubrious, the mean temperature is often found to be scarcely at all higher than that of the surrounding district, but very often some local cause, such as a range of hills, affords a shelter from cold or injurious winds. Ventnor, in the Undercliff of the Isle of Wight, is a good illustration of this fact, and hence it is a favourite winter residence for invalids. Not only is it sheltered from the cold east winds, but its proximity to the sea raises its winter temperature several degrees.

Forests likewise exert a considerable influence on climate and mean temperature. Trees, like all other bodies, become greatly heated by the sun's rays. They do not, however, acquiro their maximum temperature till a little after sunset, while the maximum temperature of the air is attained about two or three o'clock. They also change their temperature much more slowly than the air around them. Hence they make the days cooler and the nights warmer, and thus render the climate more mild, imparting to it somewhat of the insular character. They also exert a considerable influence on the evaporation from the earth, and increase the humidity of the air. In this way they serve to increase the rainfall of any district.

In some places, where a large expanse of country has been cleared of most of the forests, the difference in the rainfall has been shown by the partial drying up of rivers and lakes.

Not only is the influence of the mean temperature upon man distinctly seen and felt, but it also exerts a great influence on the distribution of plants, the limits to the cultivation of various trees and varieties of grain being almost coincident with some of the isothermal lines already referred to.

the Epicurean tried to account for ambition, by saying that our love for the approbation of others only exists in so far as it enables us to gratify our sensual appetites; and for compassion by saying, that it merely springs from our knowledge that, if we do not assist others, they will not assist us. But although this theory has the merit of simplicity to recommend it, it fails to account for all the appearances presented by men's actions. If we take the case of ambition, or regard for the esteem of others, many (Lucretia, for instance), in order to preserve the good opinion of their fellows, have even sacrificed their lives, by which they knowingly destroyed all future means of gratifying their sensual appetites. Or let us take the pleasure men feel in doing good to, or relieving the misery of, others; no doubt men may and often do act in this way from a love of fame, or a love of power; but then it is equally true that they often, perhaps oftener, do not act from such motives at all, i.e., they are influenced, not by their appetites, but by what are called their afections. Nor can the Epicurean theory account for such phenomena as men's pursuing knowledge for its own sake without any consideration of the use it can be put to, but merely because they like to do so, because it ignores the existence of the desires, and recognises no pleasures except those of the body. Hence, from observation of the differences existing amongst the various principles of our nature, we may divide them into three classes:-1, Appetites; 2, Desires; 3, Affections.

Our Appetites (at least such of them as are natural and not acquired) are common to us with the brutes, the chief of them being hunger and thirst, which were intended for our preservation. Besides such natural appetites, there are others which are acquired, such as that for tobacco or for opium.

The Desires, unlike the appetites, have not their origin in the body, and they are also more continuous in their operation. The chief of them are five:-1, The Desire of Power; 2, The Desire of Esteem; 3, The Desire of Knowledge; 4, The Desire of Superiority; and, 5, The Desire of Society.

The Affections include all those principles of our nature whose object is the communication of enjoyment or suffering to any of our fellow-creatures. They naturally divide themselves into the benevolent and the malevolent affections; the former including love, patriotism, friendship, benevolence, gratitude, pity, etc.; and the latter, hatred, envy, resentment, jealousy, revenge, etc. The term passion is applied generally to any of these principles of our nature, when they pass beyond their proper limit. We may now consider the two questions already stated; and, naturally, the first subject of inquiry in reference to the principles which actuate men's conduct is, what is meant by virtue and vice-wherein do they really consist? what is the particular character of the conduct, or act, or temper of mind to which we apply the terms virtuous or vicious respectively? what is it that we see in one character which excites in us approbation, esteem, and praise, and in another disapprobation, contempt, and blame?

It is possible that, at first sight, to a mind not much accustomed to reflection, it might seem that these questions did not possess much difficulty; or, at all events, that all must agree in the answers to be given. The matter, however, will not appear so simple or easy when it is remembered that the standard by which actions are to be tried has varied at different times in the history of the world; that the acts which at one time or in one country were considered even praiseworthy, have, at another time or in another country, been visited with the severest blame; and that even amongst civilised countries at the present day there is by no means complete unanimity as to the light in which various particular actions are to be esteemed. These csiderations have even led some persons to imagine that there really no fixed and determinate standard of moral right and wrong at all; but merely that that is virtuous or vicious which happens to be accounted so in a particular nation at a particular time. But is this really so? Is there no test except praise or blame by which it can be surely decided whether an action is virtuous or not? To these questions, amongst other things, the science of Ethics attempts to give a satisfactory reply. Assuming, however, for the present that there is in reality a fized criterion or standard of virtue and vice-that there is a real difference between right and wrong-let us see what are the chief accounts which have been given of the nature of virtue. Partly adopting as a basis the classification of them given by Adam Smith, it may be stated generally that the

principal may be reduced to three classes, according as they resolve virtue into propriety, prudence, or disinterested benevolence, which we must consider separately, though it will not be possible to examine them accurately in detail.

By virtue, consisting in propriety of conduct, is meant that it consists in the suitableness of the affection from which a man acts to the object by which it is excited. This was the foundation of the Platonic, Aristotelian, and Stoical systems.

The soul, according to Plato, was composed of three faculties or parts, called the rational, irascible (including, for example, ambition, animosity, emulation, and revenge), and concupiscent (ie., all passions founded in the love of pleasure, and including all the bodily and sensual appetites). Justice, the greatest of all virtues, and which comprehended in it prudence, fortitude, temperance, and the rest, existed when the three parts or faculties of the soul were in a state of balance, and confined themselves each to its proper place, without either interfering with the province of the other. Hence he represented virtue as the harmony of the soul, or as a state of perfect health; and compared it to a well-ordered republic, in which the wise laws of the ruler were promptly and cheerfully obeyed by the ruled. Aristotle regarded each of the virtues as a mean lying between two opposite vices, one of which has too much and the other too little of some particular quality-the quality being the being duly and properly affected by some particular class of objects. Thus, courage is the mean between the vices of cowardice on the one hand, and rashness on the other; the former of which consists in being too much, and the latter in being too little, affected by the objects of fear. So frugality lies in a mean between avarice, an excess, and profusion, a defect, in attending to the objects of self-interest.

Zeno, the founder of the great Stoical school, taught that virtue consisted in choosing or rejecting the different objects of choice presented to us, according as they were by nature constituted more or less the objects of choice or rejection for us. Every animal was, at its birth, entrusted to its own care by nature, and was endowed for this purpose with self-love, that it might try to preserve, not only its existence, but also all the different parts of its nature, in their most perfect state. Whatever, therefore, tended to this preservation, was pointed out by nature as an object of choice, and whatever had a contrary tendency was similarly pointed out as an object of rejection. Some, however, of the objects in each class were more the objects of choice or rejection, as the case might be, than others: for example, health was preferable to strength, strength to agility, and reputation to power; and so, also, sickness was more to be rejected than unwieldiness of body, ignominy than poverty, and poverty than the loss of power. And, accordingly, it was in choosing those objects which, out of several presented to us of which we could not obtain all, were most to be chosen ; and, in like manner, rejecting those which were most to be rejected when we could not reject all, that virtue consisted.

Several modern writers on Ethics have also regarded virtue as ultimately resolvable into propriety of conduct. Clarke makes it consist in a conduct conformable to the fitness of things, and Wollaston in a conduct conformable to truth.

The earliest philosopher who made virtue to consist in prudence was Epicurus. According to him, bodily pleasure and pain are the sole ultimate objects of desire and aversion; and anything else is desired or shunned only from its tendency to procure us such pleasure or save us from such pain. "All other virtues," he said, "grow from prudence, which teaches that we cannot live pleasurably without living justly and virtuously, nor live justly and virtuously without living pleasurably." And although he regarded the pleasures and pains of the mind as infinitely greater than those of the body, yet, according to his view, the former were always ultimately resolvable into the latter; i.e., the pleasures and pains of the mind were derived from the recollection and anticipation of those of the body. None of the virtues were, in this system, to be pursued upon their own account, but only because they tended to secure the greatest happiness which man can enjoy. In this respect Epicurus was wrong, though he was clearly right in his statement that a virtuous course of conduct is necessary to happiness.

Hutcheson and others (such as Cudworth and More) have made virtue to consist in benevolence, or love; which, as it was according to them the sole principle of action with the Deity, so it was the only praiseworthy motive to action with man.

"In

8. We have pointed out that 65 indicates that five sixes have been multiplied together to form the quantities which it represents; and similarly with 61. Hence it is obvious that to multiply 65 by 6 we should have to multiply the product of five sixes by the product of four sixes-obtaining, obviously, the product of nine sixes, or 6". Hence a simple rule to multiply two powers of the same number:-Add their indices.

9. The same rule applies for fractional indices—that is, for roots; thus7294 = 3; 7293 = 0.

7293 X 7268 = 9 × 3; or 729$ + b = 7291 = 27.

10. In a similar way, the division of quantities expressed in the form of powers of the same number is accomplished by the subtraction of the less from the greater index. Thus 65 indicates five sixes multiplied together; 6 the same for four sixes. Hence, if 6 be written as a denominator, it is evident that the four sixes of which it is composed will cut out four of those of which 65 is composed, and leave in the numerator only 1 (or 4); thus

5

And so, if we have 62 and 6', and multiply together their indices, we have in reality done the same as if we had added the indices of 62, 62, 62, 62, or of 6', 6'-that is, we have done the same as raise 62 to its fourth power, or 6' to its second power. Hence it is obvious that when the index of any power is multiplied by any quantity, that power is itself raised to the power of that quantity; thus

62×+ = (G2)* = 364; and 6+×2 = (6*)2 = 1296*.

one country have been looked upon with little, if any, disfavour, have been in another age or in another country viewed in a very different light. But yet it is true that, universally, there has existed a standard of some sort by which actions have been judged, and that, according to their conformity or non-conformity to this, they are visited with praise or blame. Now, what is the true nature of this rule? whence are men led to seek after it and to judge actions by it? what is its origin, and within what limits is it confined? These, and questions like them, are those which the science of Ethics investigates and seeks to determine; and it is in the answers given that the different ethical systems differ from each other.

Although of ancient origin, Ethics did not engage the attention of mankind at as early a period in the history of the world as many other sciences of less real importance. The phenomena of external nature, and the sciences which aim at turning them to practical account, naturally engaged the attention of man before he commenced to turn his mind in upon itself and examine the laws by which he thinks, or in conformity to which he acts. Still, Ethical Science was cultivated very largely in ancient times. Many of the Greek philosophers not only wrote much, but thought deeply, upon the subject; and the germs of many, if not of all, the most elaborate modern systems of Ethics may be found in Plato, the earliest moral philosopher whose writings have come down to us; though he quotes many predecessors of whom nothing has survived except their names. Plato more in words than in reality; and, after him, the progress Aristotle, who came next, seems, indeed, to have differed with of ethical philosophy was considerably advanced in the disputes between the rival schools of the Stoics and Epicureans.

The Romans borrowed their notions of moral philosophy, as

they did so much else, from the Greeks; but contributed little, if anything, themselves to the most important principles of the

science.

For nearly two thousand years after the close of ancient philosophy, the history of Ethics presents a blank, until the time of the schoolmen, who, directly or indirectly, first revived in modern times many of the most important questions in morals; although they hardly treated at all, or left entirely out of view, many of its most essential features. It is, however, from the writings of Hobbes, in the early part of the seventeenth century, that the commencement of modern Ethics must be dated; and from that period downwards there has been a continuous succession of ethical writers, comprising Cudworth, tosh, and a multitude of others, some of whom we may subseMalebranche, Butler, Hume, Smith, Hartley, Bentham, Mackinquently have occasion to refer to more particularly.

In order to obtain a general conception of the leading prin

ciples of Ethical or Moral Science, we may consider it as Secondly, "What is it in our minds which recommends virtue to involving two great questions:-Firstly, "What is virtue?" us for our adoption ?"

If we thoroughly understand the meaning of these two ques

G3 = (G3)• = (6•,3 ;

time given to them by different systems, we shall have become acquainted with the chief features of Ethical Science. Before, however, we proceed to consider these questions in detail, it is

273 = (272) = (729) = 9; or 273 = (273)1⁄2 = (3)2 = 9 14. It will be observed that we have made no reference to the index 0. Remembering that any number divided by itself

gives unity as a quotient, we have

66 ÷ 66 = 6o-660 1.

Hence we arrive at the apparent paradox that any number raised to the zero power is equal to unity-an arithmetical curiosity, which the reader must be content to receive without further explanation.

nature can be classified.

The Epicurean theory, which was, perhaps, the oldest of all, admitted only one principle of human nature, into which every other was capable of being ultimately resolved. In the system of Epicurus our sole principles of action were the appetites, which had their origin in the body, and the means of gratifying which were furnished by the senses; and the sole object of man's existence was to gratify these sensual appetites. Such & theory as this is contradicted by the simple but obvious fact that men do not gratify such appetites only for instance, they are often influenced by ambition and compassion. True,