You see, then, in the first instance, that a beautiful cup is formed. As the air comes to the candle, it moves upwards by the force of the current which the heat of the candle produces, and it so cools all the sides of the wax, tallow, or fuel as to keep the edge much cooler than the part within; the part within melts by the flame that runs down the wick as far as it can go before it is stopped, but the part on the outside does not melt. If I made a current in one direction, my cup would be lopsided, and the fluid would consequently run over--for the same force of gravity which holds worlds together, holds this fluid in a horizontal position. You see, therefore, that the cup is formed by this beautifully regular ascending current of air playing upon all sides, which keeps the exterior of the candle cool. No fuel would serve for a candle which has not the property of giving this cup, except such fuel as the Irish bogwood, where the material itself is like a sponge, and holds its own fuel.

You see now why you have such a bad result if you burn those beautiful fluted candles, which are irregular, intermittent in their shape, and cannot therefore have that nicely-formed edge to the cup which is the great beauty in a candle. I hope you will now see that the perfection of a process--that is, its utility--is the better point of beauty about it.

It is not the best-looking thing, but the best-acting thing which is the most advantageous to us. This good-looking candle is a bad burning one.

There will be a guttering round about it because of the irregularity of the stream of air and the badness of the cup which is formed thereby.

You may see some pretty examples of the action of the ascending current when you have a little gutter run down the side of a candle, making it thicker there than it is elsewhere. As the candle goes on burning, that keeps its place and forms a little pillar sticking up by the side, because, as it rises higher above the rest of the wax or fuel, the air gets better round it, and it is more cooled and better able to resist the action of the heat at a little distance. Now, the greatest mistakes and faults with regard to candles, as in many other things, often bring with them instruction which we should not receive if they had not occurred. You will always remember that whenever a result happens, especially if it be new, you should say: "What is the cause? Why does it occur?" And you will in the course of time find out the reason.

Then there is another point about these candles which will answer a question--that is, as to the way in which this fluid gets out of the cup, up to the wick, and into the place of combustion. You know that the flames on these burning wicks in candles made of beeswax, stearine, or spermaceti, do not run down to the wax or other matter, and melt it all away, but keep to their own right place. They are fenced off from the fluid below, and do not encroach on the cup at the sides.

I cannot imagine a more beautiful example than the condition of adjustment under which a candle makes one part subserve to the other to the very end of its action. A combustible thing like that, burning away gradually, never being intruded upon by the flame, is a very beautiful sight; especially when you come to learn what a vigorous thing flame is, what power it has of destroying the wax itself when it gets hold of it, and of disturbing its proper form if it come only too near.

But how does the flame get hold of the fuel? There is a beautiful point about that. It is by what is called capillary attraction that the fuel is conveyed to the part where combustion goes on, and is deposited there, not in a careless way, but very beautifully in the very midst of the centre of action which takes place around it.

_II.--The Brightness of the Candle_

Air is absolutely necessary for combustion; and, what is more, I must have you understand that _fresh_ air is necessary, or else we should be imperfect in our reasoning and our experiments. Here is a jar of air. I place it over a candle, and it burns very nicely in it at first, showing that what I have said about it is true; but there will soon be a change.

See how the flame is drawing upwards, presently fading, and at last going out. And going out, why? Not because it wants air merely, for the jar is as full now as it was before, but it wants pure, fresh air. The jar is full of air, partly changed, partly not changed; but it does not contain sufficient of the fresh air for combustion.

Suppose I take a candle, and examine that part of it which appears brightest to our eyes. Why, there I get these black particles, which are just the smoke of the candle; and this brings to mind that old employment which Dean Swift recommended to servants for their amus.e.m.e.nt, namely, writing on the ceiling of a room with a candle. But what is that black substance? Why, it is the same carbon which exists in the candle.

It evidently existed in the candle, or else we should not have had it here. You would hardly think that all those substances which fly about London in the form of soots and blacks are the very beauty and life of the flame. Here is a piece of wire gauze which will not let the flame go through it, and I think you will see, almost immediately, that, when I bring it low enough to touch that part of the flame which is otherwise so bright, it quells and quenches it at once, and allows a volume of smoke to rise up.

Whenever a substance burns without a.s.suming the vaporous state--whether it becomes liquid or remains solid--it becomes exceedingly luminous.

What I say is applicable to all substances--whether they burn or whether they do not burn--that they are exceedingly bright if they retain their solid state when heated, and that it is to this presence of solid particles in the candle-flame that it owes its brilliancy.

I have here a piece of carbon, or charcoal, which will burn and give us light exactly in the same manner as if it were burnt as part of a candle. The heat that is in the flame of a candle decomposes the vapour of the wax, and sets free the carbon particles--they rise up heated and glowing as this now glows, and then enter into the air. But the particles when burnt never pa.s.s off from a candle in the form of carbon.

They go off into the air as a perfectly invisible substance, about which we shall know hereafter.

Is it not beautiful to think that such a process is going on, and that such a dirty thing as charcoal can become so incandescent? You see, it comes to this--that all bright flames contain these solid particles; all things that burn and produce solid particles, either during the time they are burning, as in the candle, or immediately after being burnt, as in the case of the gunpowder and iron-filings--all these things give us this glorious and beautiful light.

_III.--The Products of Combustion_

We observe that there are certain products as the result of the combustion of a candle, and that of these products one portion may be considered as charcoal, or soot; that charcoal, when afterwards burnt, produces some other product--carbonic acid, as we shall see; and it concerns us very much now to ascertain what yet a third product is.

Suppose I take a candle and place it under a jar. You see that the sides of the jar become cloudy, and the light begins to burn feebly. It is the products, you see, which make the light so dim, and this is the same thing which makes the sides of the jar so opaque. If you go home and take a spoon that has been in the cold air, and hold it over a candle--not so as to soot it--you will find that it becomes dim, just as that jar is dim. If you can get a silver dish, or something of that kind, you will make the experiment still better. It is _water_ which causes the dimness, and we can make it, without difficulty, a.s.sume the form of a liquid.

And so we can go on with almost all combustible substances, and we find that if they burn with a flame, as a candle, they produce water. You may make these experiments yourselves. The head of a poker is a very good thing to try with, and if it remains cold long enough over the candle, you may get water condensed in drops on it; or a spoon, or a ladle, or anything else may be used, provided it be clean, and can carry off the heat, and so condense the water.

And now--to go into the history of this wonderful production of water from combustibles, and by combustion--I must first of all tell you that this water may exist in different conditions; and although you may now be acquainted with all its forms, they still require us to give a little attention to them for the present, so that we may perceive how the water, whilst it goes through its protean changes, is entirely and absolutely the same thing, whether it is produced from a candle, by combustion, or from the rivers or ocean.

First of all, water, when at the coldest, is ice. Now, we speak of water as water; whether it be in its solid, or liquid, or gaseous state, we speak of it chemically as water.

We shall not in future be deceived, therefore, by any changes that are produced in water. Water is the same everywhere, whether produced from the ocean or from the flame of the candle. Where, then, is this water which we get from a candle? It evidently comes, as to part of it, from the candle; but is it within the candle beforehand? No! It is not in the candle; and it is not in the air round about the candle, which is necessary for its combustion. It is neither in one nor the other, but it comes from their conjoint action, a part from the candle, a part from the air. And this we have now to trace.

If we decompose water we can obtain from it a gas. This is hydrogen--a body cla.s.sed amongst those things in chemistry which we call elements, because we can get nothing else out of them. A candle is not an elementary body, because we can get carbon out of it; we can get this hydrogen out of it, or at least out of the water which it supplies. And this gas has been so named hydrogen because it is that element which, in a.s.sociation with another, generates water.

Hydrogen gives rise to no substance that can become solid, either during combustion or afterwards, as a product of its combustion. But when it burns it produces water only; and if we take a cold gla.s.s and put it over the flame, it becomes damp, and you have water produced immediately in appreciable quant.i.ty, and nothing is produced by its combustion but the same water which you have seen the flame of a candle produce. This hydrogen is the only thing in Nature that furnishes water as the sole product of combustion.

Water can be decomposed by electricity, and then we find that its other const.i.tuent is the gas oxygen in which, as can easily be shown, a candle or a lamp burns much more brilliantly than it does in air, but produces the same products as when it burns in air. We thus find that oxygen is a const.i.tuent of the air, and by burning something in the air we can remove the oxygen therefrom, leaving behind for our study the nitrogen, which const.i.tutes about four-fifths of the air, the oxygen accounting for nearly all the rest.

The other great product of the burning of a candle is carbonic acid--a gas formed by the union of the carbon of the candle and the oxygen of the air. Whenever carbon burns, whether in a candle or in a living creature, it produces carbonic acid.

_IV.--Combustion and Respiration_

Now I must take you to a very interesting part of our subject--to the relation between the combustion of a candle and that living kind of combustion which goes on within us. In every one of us there is a living process of combustion going on very similar to that of a candle. For it is not merely true in a poetical sense--the relation of the life of man to a taper. A candle will burn some four, five, six, or seven hours.

What, then, must be the daily amount of carbon going up into the air in the way of carbonic acid? What a quant.i.ty of carbon must go from each of us in respiration! A man in twenty-four hours converts as much as seven ounces of carbon into carbonic acid; a milch cow will convert seventy ounces, and a horse seventy-nine ounces, solely by the act of respiration. That is, the horse in twenty-four hours burns seventy-nine ounces of charcoal, or carbon, in his organs of respiration to supply his natural warmth in that time.

All the warm-blooded animals get their warmth in this way, by the conversion of carbon; not in a free state, but in a state of combination. And what an extraordinary notion this gives us of the alterations going out in our atmosphere! As much as 5,000,000 pounds of carbonic acid is formed by respiration in London alone in twenty-four hours. And where does all this go? Up into the air. If the carbon had been like lead or iron, which, in burning, produces a solid substance, what would happen? Combustion would not go on. As charcoal burns, it becomes a vapour and pa.s.ses off into the atmosphere, which is the great vehicle, the great carrier, for conveying it away to other places. Then, what becomes of it?

Wonderful is it to find that the change produced by respiration, which seems so injurious to us, for we cannot breathe air twice over, is the very life and support of plants and vegetables that grow upon the surface of the earth. It is the same also under the surface in the great bodies of water, for fishes and other animals respire upon the same principle, though not exactly by contact with the open air. They respire by the oxygen which is dissolved from the air by the water, and form carbonic acid; and they all move about to produce the one great work of making the animal and vegetable kingdoms subservient to each other.

All the plants growing upon the surface of the earth absorb carbon.

These leaves are taking up their carbon from the atmosphere, to which we have given it in the form of carbonic acid, and they are prospering.

Give them a pure air like ours, and they could not live in it; give them carbon with other matters, and they live and rejoice. So are we made dependent not merely upon our fellow-creatures, but upon our fellow-existers, all Nature being tied by the laws that make one part conduce to the good of the other.

AUGUSTE FOREL

The Senses of Insects

Auguste Forel, who in 1909 retired from the Chair of Morbid Psychology in the University of Zurich, was born on September 1, 1848, and is one of the greatest students of the minds and senses of the lower animals and mankind. Among his most famous works are his "Hygiene of Nerves and Mind," his great treatise on the whole problem of s.e.x in human life, of which a cheap edition ent.i.tled "s.e.xual Ethics" is published, his work on hypnotism, and his numerous contributions to the psychology of insects. The chief studies of this remarkable and ill.u.s.trious student and thinker for many decades past have been those of the senses and mental faculties of insects. He has recorded the fact that his study of the beehive led him to his present views as to the right const.i.tution of the state--views which may be described as socialism with a difference. His work on insects has served the study of human psychology, and is in itself the most important contribution to insect psychology ever made by a single student.

Only within the last two years has the work of Forel, long famous on the European Continent, begun to be known abroad.

_I.--Insect Activity and Instinct_

This subject is one of great interest, as much from the standpoint of biology as from that of comparative psychology. The very peculiar mechanism of instincts always has its starting-point in sensations. To comprehend this mechanism it is essential to understand thoroughly the organs of sense and their special functions.

It is further necessary to study the co-ordination which exists between the action of the different senses, and leads to their intimate connection with the functions of the nerve-centres, that is to say, with the specially instinctive intelligence of insects. The whole question is, therefore, a chapter of comparative psychology, a chapter in which it is necessary to take careful note of every factor, to place oneself, so to speak, on a level with the mind of an insect, and, above all, to avoid the anthropomorphic errors with which works upon the subject are filled.

At the same time the other extreme must equally be avoided--"anthropophobia," which at all costs desires to see in every living organism a "machine," forgetting that a "machine" which lives, that is to say, which grows, takes in nutriment, and strikes a balance between income and expenditure, which, in a word, continually reconstructs itself, is not a "machine," but something entirely different. In other words, it is necessary to steer clear of two dangers. We must avoid (1) identifying the mind of an insect with our own, but, above all, (2) imagining that we, with what knowledge we possess, can reconstruct the mind by our chemical and physical laws.

On the other hand, we have to recognise the fact that this mind, and the sensory functions which put it on its guard, are derived, just as with our human selves, from the primitive protoplasmic life. This life, so far as it is specialised in the nervous system by nerve irritability and its connections with the muscular system, is manifested under two aspects. These may be likened to two branches of one trunk.

(_a_) _Automatic_ or _instinctive_ activity. This, though perfected by repet.i.tion, is definitely inherited. It is uncontrollable and constant in effect, adapted to the circ.u.mstances of the special life of the race in question. It is this curious instinctive adaptation--which is so intelligent when it carries out its proper task, so stupid and incapable when diverted to some other purpose--that has deceived so many scientists and philosophers by its insidious a.n.a.logy with humanly constructed machines.

But, automatic as it may appear, instinct is not invariable. In the first place, it presents a racial evolution which of itself alone already demonstrates a certain degree of plasticity from generation to generation. It presents, further, individual variations which are more distinct as it is less deeply fixed by heredity. Thus the divergent instincts of two varieties, _e.g._, of insects, present more individual variability and adaptability than do those instincts common to all species of a genus. In short, if we carefully study the behaviour of each individual of a species of insects with a developed brain (as has been done by P. Huber, Lubbock, Wasmann, and myself, among others, for bees, wasps, and ants), we are not long in finding noteworthy differences, especially when we put the instinct under abnormal conditions. We then force the nervous activity of these insects to present a second and plastic aspect, which to a large extent has been hidden from us under their enormously developed instinct.

(_b_) The _plastic_ or _adaptive_ activity is by no means, as has been so often suggested, a derivative of instinct. It is primitive. It is even the fundamental condition of the evolution of life. The living being is distinguished by its power of adaptation; even the amoeba is plastic. But in order that one individual may adapt itself to a host of conditions and possibilities, as is the case with the higher mammals and especially with man, the brain requires an enormous quant.i.ty of nerve elements. But this is not the case with the fixed and specialised adaptation of instinct.

In secondary automatism, or habit, which we observe in ourselves, it is easy to study how this activity, derived from plastic activity, and ever becoming more prompt, complex, and sure (technical habits), necessitates less and less expenditure of nerve effort. It is very difficult to understand how inherited instinct, hereditary automatism, could have originated from the plastic activities of our ancestors. It seems as if a very slow selection, among individuals best adapted in consequence of fortunate parentage, might perhaps account for it.

To sum up, every animal possesses two kinds of activity in varying degrees, sometimes one, sometimes the other predominating. In the lowest beings they are both rudimentary. In insects, special automatic activity reaches the summit of development and predominance; in man, on the contrary, with his great brain development, plastic activity is elevated to an extraordinary height, above all by language, and before all by written language, which subst.i.tutes graphic fixation for secondary automatism, and allows the acc.u.mulation outside the brain of the knowledge of past generations, thus serving his plastic activity, at once the adapter and combiner of what the past has bequeathed to it.