Electricity is not a fluid, or any form of material substance, but a form of energy. Energy is expressed in different ways, and, while as energy it is one and the same, we call it by different names--as heat energy, chemical energy, electrical energy, and so on. They will all do work, and in that respect are alike. One difficulty in explaining electrical phenomena is the nomenclature that the science is loaded down with. All the old names were adopted when electricity was regarded as a fluid, hence the word "current." It is spoken of as "flowing" when it does not flow any more than light flows.
If a man wants to write a treatise on electricity--outside of the mere phenomena and applications--and wants to make a large book of it, he would better tell what he does not know about it, for in that way he can make a volume of almost any size. But if he wants to tell what it really is, and what he really knows it is, a primer will be large enough. This much we know--that it is one of many expressions of energy.
Chemistry teaches that heat is directly related to the atoms of matter.
Atoms of different substances differ greatly in weight. For instance, the hydrogen atom is the unit of atomic weight, because it is the lightest of all of them. Taking the hydrogen atom as the unit, in round numbers the iron atom weighs as much as 56 atoms of hydrogen, copper a little over 63, silver 108, gold 197. Heat acts upon matter according to the number of atoms in a given s.p.a.ce, and not as its weight. Knowing the relative weights of the atoms of the different metals named, it would be possible to determine by weight the dimensions of different pieces of metal so that they will contain an equal number of atoms. If we take pieces of iron, copper, silver and gold, each of such weight as that all the pieces will contain the same number of atoms, and subject them to heat till all are raised to the same temperature, it will be found that they have all absorbed practically the same quant.i.ty of heat without regard to the different weights of matter. It will be observed that the piece of silver, for instance, will have to weigh nearly twice as much as the iron in order to contain the same number of atoms, but it will absorb the same amount of heat as the piece of iron containing the same number of atoms, if both are raised to the same temperature. In view of the above fact it seems that heat acts especially upon the atoms of matter and is a peculiar form of atomic motion. Heat is one kind of motion of the atoms, while electricity may be another form of motion of the same. The two motions may be carried on together. The earth has a compound motion. It revolves upon its axis once in twenty-four hours, and it also revolves around the sun once each year. So you see that there are different kinds of motion that may be communicated to the same body--all producing different results.
The motion of the individual atom as heat may be, and is, as rapid as light itself when the temperature is sufficiently high, but it does not travel along a conductor rapidly as the electro-atomic motion will. If we apply heat to the end of a metal rod it will travel slowly along the rod. But if we make the rod a conductor of electricity it travels from atom to atom with a speed nearer that of the light ray through the ether. Some modern writers have attempted to explain all the phenomena of electricity as having their origin in a certain play of forces upon the ether, and there is no doubt but that the ether plays an important part in all electrical phenomena as a medium through which energy is transferred; but ether-waves that are set in motion by the electrical excitation of ordinary matter are no more electricity than the ether-waves set up by the sun in the cold regions of s.p.a.ce are heat.
They become heat only when they strike matter. Heat, _as such_, begins and ends in matter;--so (I believe) does electricity.
Do not be discouraged with these feeble attempts to explain the theory of electricity. All I even hope to do is to establish in your minds this fundamental thought, to wit, that there is really but one Energy, and that it is always expressed by some form of motion or the ability to create motion. Motions differ, and hence are called by different names.
If I should set an emery-wheel to revolving and hold a piece of steel against it the piece of steel would become heated and incandescent particles would fly off, making a brilliant display of fireworks. The heat that has been developed is the measure of the mechanical energy that I have used against the emery-wheel. Now, let us subst.i.tute for the emery-wheel another wheel of the same size made of vulcanized rubber, gla.s.s or resin. I set it to revolving at the same speed, and instead of the piece of steel, I now hold a silk handkerchief or a catskin against the wheel with the same force that I did the steel. If now I provide a Leyden jar and some points to gather up the electricity that will be produced (instead of the heat generated in the other case), it would be found that the energy developed in the one case would exactly balance that of the other, if it were all gathered up and put into work. The electricity stored in the jar is in a state of strain, like a bent bow, and will recoil, when it has a chance, with a power commensurate with the time it has been storing and the amount of energy used in pressing against the wheel.
If now I connect my two hands, one with the inside and the other with the outside of the jar, this stored energy will strike me with a force equal to all the energy I have previously expended in pressing against the wheel, minus the loss in heat. If I did it for a long enough time this electrical spring would be wound up to such a tension that the recoil would destroy life if one put himself in the path of its discharge. If all the heat in the first case were gathered up and made to bend a stiff spring, and one should put himself in its way when released, this mechanical spring would strike with the same power that the electrical spring did when the Leyden jar was discharged. This statement a.s.sumes that all the energy in the second experiment was stored as electricity in the jar. You will be able to see from the above ill.u.s.tration that heat, electrical energy, and mechanical energy are really the same. Then you ask, how do they differ? Simply in their phenomena--their outward manifestations.
While there is much that we cannot know about any of the phenomena of nature, it is a great step in advance if we can establish a close relationship between them. It helps to free electricity from many vagaries that exist in the minds of most people regarding it; vagaries that in ignorant minds amount to superst.i.tion. While it possesses wonderful powers, they give it attributes that it does not possess. Not long ago a favorite headline of the medical electrician"s advertis.e.m.e.nt was "Electricity Is Life," and it was a common thing to see street-venders dealing out this "life" in shocking quant.i.ties to the innocent mult.i.tudes--ten cents" worth in as many seconds.
Science divides electricity into two kinds--static and dynamic. Static comes from a Greek word, meaning to stand, and refers to electricity as a stationary charge. Dynamic is from the Greek word meaning power, and refers to electricity in motion. When Franklin made his celebrated kite experiment, the electricity came down the string, and from the key on the end of the string he stored it in a Leyden jar. While the electricity was moving down the string it was dynamic, but as soon as it was stored in the Leyden jar it became static. Current electricity is dynamic. A closed telegraphic circuit is charged dynamically, while the prime conductor of a frictional electric machine is charged statically.
The distinction is arbitrary and in a sense a misnomer. When we rub a piece of hard rubber with a catskin it is statically charged because the substances are what are called non-conductors, and the charge cannot be conducted readily away. All substances are divided into two cla.s.ses, to wit, conductors or non-electrics, and non-conductors or electrics, more commonly called dielectrics. These, however, are relative terms, as no substance is either a perfect conductor or a perfect non-conductor.
The metals, beginning with silver as the best, are conductors. Ebonite, paraffine, sh.e.l.lac, etc., are insulators, or very poor conductors. The best conductors offer some resistance to the pa.s.sage of the current and the best insulators conduct to some extent. If we make a comparison of electric conductors we find that the metals that conduct heat best also conduct electricity best. This, it seems to me, is a confirmation of the atomic theory of electricity so far as it means anything. If a good conductor, as silver, is subjected to intense cold by putting it into liquid air, its conductivity is greatly increased. It is well known that heating a conductor ordinarily diminishes its power to conduct electricity. This shows that, in order that electrical motion of the atom may have free play, the heat motion must be suppressed.
CHAPTER VI.
ELECTRIC CURRENTS.
The simplest form of an electric machine is one in which the operator is a prominent part of the operation. Electricity, like magnetism, operates in a closed circuit, even when it is static--so-called. Take a stick of sealing-wax, say, in your left hand, and rub it with a piece of fur or silk with your right hand, and you have the simplest form of electric machine--the one that was known to the ancients, and the one from which the science, great as it is to-day, had its beginnings. The stick of sealing-wax is one element of the battery, and the piece of fur or silk is the other, while your hands, arm and body form the conductor that connects the two poles, and the friction is the exciting agent and may be said to take the place of the fluid of a battery. The electrical conditions are not wholly static, as a slow current is pa.s.sing around through your arms and body from one pole to the other. Even if the conditions were wholly static there would be polarized lines of force, in a state of strain, reaching around in a closed circuit.
If we rub the wax with the fur and then take it away the wax has a charge of electricity and will attract light objects. If we had rubbed a piece of metal or some good conductor it would have been warmed instead of electrified. In both cases the particles of the substances have been affected, and if the atomic theory is correct--and it seems plausible--in the former case the atoms are partly put into electrical motion and partly into a state of electrical strain that we call static (standing) electricity; while in the latter case the atoms are put into the peculiar motion that belongs to heat. The former we call electricity, and the latter we call heat. The electro-atomic motion under some circ.u.mstances readily turns to heat, which seems to be the tendency of all forms of energy. The electric light is a result of this tendency. All non-conductors, or electrics, have a complex molecular structure, and, while their atoms when subjected to friction are put into a state of electrostatic strain, they are not able readily to respond as a conductor of dynamic electricity. The electric-light filament in the incandescent lamp is a much poorer conductor than the copper wire that leads up to it. The copper wire is readily responsive to the electrical influence, but the carbon filament is not. So electrical action that freely pa.s.ses along the wire, is resisted and becomes heat action in the filament, and light is the attendant of intense heat. But, to go back to the sources of electricity.
Frictional electric machines have been constructed in great variety.
All, however, embrace the essentials set forth in the sealing-wax experiment, and would be difficult to describe without cuts. Let us, therefore, consider another source of electricity, which was the outgrowth of the discovery of Galvani (or rather his wife), and reduced to concrete form by Volta. We refer to the galvanic or voltaic battery.
If we put a bar of zinc into a gla.s.s vessel and pour sulphuric acid and water into it, there will be a boiling, and an evolution of hydrogen gas, and energy is released in the form of heat, so that the fluid and the gla.s.s vessel become heated. Now let us put a bar of copper or a stick of carbon into the gla.s.s, but not in contact with the zinc; connect the ends (that are not immersed) of the two elements--copper and zinc--with a metal wire or any conductor, and a new condition is set up.
Heat is no longer evolved to the same extent, but most of the energy becomes electrical in character, and an electrical chain of action takes place in the circuit that has now been formed. Taking the zinc as the starting point, the so-called current flows from the zinc through the fluid to the copper and from the copper through the wire to the zinc.
A chain of polarized atomic activity is established in the circuit, similar to the closed circuit of magnetic lines of force, only the latter is static, while the former is dynamic.
You ask what is the difference? Well, it is much easier to ask a question than it is to answer it. You will remember that in the chapter on magnetism it was stated that the molecules of a magnet were little natural magnets, and that their attractions were satisfied within themselves; that when their local attachments were broken up and all their like poles turned in one direction they could act upon other pieces of iron outside of the magnet. Outside and between the poles there are magnetic lines of force reaching out from one pole to the other. If we put a piece of iron across the poles these lines of force are gathered up and pa.s.s through the iron. This is purely a static condition. Let us go back to the cell of battery. When the elements are in position (the copper, the acidulated water and the zinc), and the two wires attached to the two metals which are the two poles of the battery not yet connected, there is a condition induced in these two wires that did not exist before the acidulated water was poured in, although the circuit is not yet established. If we test the two wires we find a difference of potential--a state of strain, so to speak--that did not exist before the acid acted on the zinc and liberated what was stored energy. It is in a static condition, like the magnet, and electrical lines of force are reaching out from both wires so that the ether is in a state of strain between the two poles. The air molecules may partake of it, but we have to bring in the ether as a substance, because the same conditions would practically exist if the two wires were in a vacuum. If now we connect the two wires, we have established a metallic circuit between the two poles of the battery, the static conditions are relieved, the lines of force are gathered up into the wire, and the phenomenon that we call a current is established and we have dynamic or moving electricity.
Having established the so-called electric current we will now try to show you that there really is no current. The idea of a current involves the idea of a fluid substance flowing from one point to another. When you were a boy did you never set up a row of bricks on their ends, just far enough apart so that if you pushed one over they all fell one after another? Now, imagine rows of molecules or atoms, and in your imagination they may be arranged like the bricks, so that they are affected one by the other successively with a rapidity that is akin to that of light-waves, and you can conceive how a motion may be communicated from end to end of a wire hundreds of miles in length in a small fraction of a second, and no material substance has been carried through the wire--only energy. We do not mean to say that the row of bricks ill.u.s.trates the exact mode of molecular or atomic motion that takes place in a conductor. What we mean is, that in some way motion is pa.s.sed along from atom to atom.
To give you a better conception of an electric current, let us go back of the galvanic cell to the electric machine. If both poles of the machine are attached to rods terminating in round k.n.o.bs we can set the machine in action and keep up a steady stream of disruptive discharges that will, if their frequency is great enough, perform the function of a current, and we have dynamic electricity from a statical machine; when the acid of the galvanic battery breaks down a molecule of zinc, energy is set free, and in the battery we have what corresponds to a disruptive discharge of infinitesimal proportions. This discharge would have been immediately converted into heat energy if the copper element had been left out of the battery, but as it is, it impresses itself on the atomic "brick" next to it, which establishes a chain of atomic movement throughout the circuit. This may const.i.tute, if you please, a line of electrical force. But as thousands of these disruptive discharges are taking place simultaneously as many different lines of force are established. You must not conceive of these chains of atoms as simply thrown down like the bricks and left lying there, but that the atom is active; that it has the power to pick itself up again in an infinitesimally short time and is again knocked down (following the ill.u.s.tration of the bricks) by the next discharge along its line or chain of atoms.
If you could get a mental picture of this action you would see that the whole conductor is in a most violent state of atomic motion of a peculiar kind. At the same time a part of this electrical motion is being converted into a heat motion of the atoms, and finally it all returns to heat unless some of it is stored up somewhere as potential energy. If the current has driven a motor that has wound up a weight, a part is stored up in the weight, which has the ability to do work if it is allowed to run down. If it drives machinery as it runs down, the mechanical motion is the expression of the stored energy. When the weight has run down the energy will be represented by the heat created by friction of the journals of the wheels and pulleys and the heating of the air. If the weight is allowed to fall suddenly it will heat the air to some extent, but mostly the earth and the weight itself will be heated. If the source of energy (the battery) is great and the pressure high and the conductor is too small to carry the energy developed in the battery as electricity, heat is developed, and if the heat is sufficiently intense, light also.
We have seen (Vol. II) that heat motion when it reaches a sufficiently high rate throws the ether into a vibratory motion that we call light.
However, this vibratory motion of the ether is set up long before it reaches the luminous stage; in other words, there are dark rays of the ether. We find that the electro-atomic motions of a conductor have the power to impress themselves upon the ether.
[Ill.u.s.tration: Fig. 1.
A is the primary line; _a_, the battery: _b_, the key. B is the secondary line in which is placed the galvanometer _c_.]
Let us try another experiment to show that this is the case, not only, but that the impressed ether can transfer these impressions to still another conductor. Suppose we stretch two parallel wires for, say, half a mile, or any distance, only a few feet apart, and make of each a complete circuit by rounding the end of the course and returning the wire to the starting point (as shown in Fig. 1). Put in one of these circuits a battery, and a circuit-breaker (a common telegraph-key), and in the other circuit a galvanometer (an instrument for detecting the presence and measuring the intensity of a galvanic current, by means of a dial and a deflecting needle or pointer). Now if we touch the key and close the circuit in A, the needle of the galvanometer in B will swing in one direction from zero on the dial; and if we release the key, breaking the circuit in A, the needle will swing back in the opposite direction. In neither case will the needle stay deflected, but will at once return to zero.
This shows that when the battery current was allowed to complete its circuit through wire A by closing its key, an electrical action was instantly felt in wire B, although there was no material connection between them other than the air, which is a non-conductor.
The current in the second circuit is called an induced current. Why this current? According to one theory, when we close the primary circuit the surrounding ether is thrown into a peculiar state of strain that we will call magnetic or electrical lines of force. When the ether wave strikes the second wire there is a molecular movement from a state of rest to a state of static strain. During the time that the molecules are moving from the normal to the strained position in sympathy with the ether we have the condition of a dynamic current, which lasts only a moment. This state of strain continues till the circuit is opened (breaking the wire-line), when all the electrical lines of force vanish and the molecular strain of the second wire is relieved, and we again have the conditions, momentarily, for a current of the opposite polarity, and the needle will swing in the opposite direction because the molecules or atoms have, in their recoil to the natural state, moved in an opposite direction.
Going back to Fig. 1, let us further study the phenomena under other conditions. In our first circuit (A) there is a battery and a circuit-breaker, which is a common telegraph-key. Now close the key so that a current will be established. (Remember that "current" is only a name for a condition of dynamic charge.) Place a piece of soft iron across the wire at right angles with the direction of the wire, when of course it will be at right angles with the direction of the current, and you will find now that the iron is more or less magnetic, depending upon the amount of current pa.s.sing through the wire. If we wind a number of turns of insulated wire through which the current is pa.s.sing around the iron the magnetism will be increased. In practice there are a certain number of turns and a certain sized wire that will give the best results with a given number of cells of battery (or a given voltage or pressure), operating in a closed circuit of a given resistance. All these questions are worked out mathematically in many standard books on the subject. It is not the intention in these talks to develop the science mathematically but to set out the fundamental physical facts and applications of electricity.
Under the conditions above named magnetism is developed in the soft iron bar. If we open the key the current will cease and the magnetism will vanish--that is to say, the molecules will turn back to their neutral position by their own attractions, as has been described in a previous chapter. Magnetism developed in this way is called electromagnetism.
(See Chap. IV.) If we use a piece of hardened steel instead of the soft iron it will become magnetic and remain so when the circuit is opened, because the natural tendency of the molecules to turn back to the neutral position is not great enough to overcome the coercive force, or molecular friction, of hardened steel, as has been also described in a previous chapter. To make the best electromagnet we need qualities of iron just the opposite from those of the permanent magnet. For the former we need the purest of soft iron, well annealed (heated to redness and slowly cooled, making it less brittle), so that its molecules are free to turn; while for the latter we need hardened steel, so that when the molecules are once wrenched into the magnetic condition they cannot, of themselves, turn back to the neutral state. The great value of the electromagnet lies in its ability to readily discharge, or go back to the neutral state, when the current is broken.
Let us now go back to the beginning of our experiment. When we closed the key and established the current through the wire we found that a piece of iron held at right angles to the wire, although not touching it, became magnetic. We have already said that when the circuit was open, the battery being in circuit, there were electrical lines of force established in the ether, between the two poles of the battery, and that they were gathered up into the conducting wire when the circuit was closed. We now find that there are other lines of force of a different nature established in the ether when the circuit is closed. These we call magnetic lines of force, or the magnetic field of the charged wire, and they are established at right angles to the direction of the current. These magnetic lines of force acting through the ether from an electrically charged conductor are able to break up the natural molecular magnetic rings, referred to in Chapter IV, and turn all their like poles in the same direction--thus making one compound magnet of the iron which in the neutral state consisted of millions of little natural magnets whose attractions were satisfied by a joining of their unlike poles.
Most writers account for all of the phenomena of induced currents in a second wire as coming directly from these magnetic lines of force developed upon closing the circuit.
So much for theory based upon a set of facts that make the theory seem probable. If you don"t like it give us a better one. If it is correct the writer claims no credit; it is merely a compilation of suggestions from many sources, including his own experience. We are simply seeking after truth. The man who is an earnest seeker after scientific truth cannot afford to pursue his investigations with any prejudice in favor of one theory more than another, unless the facts sustain him, and then he is not acting from prejudice, but is led by the facts. Many people make pets of their theories; and they become attached to them as they do their children; and they look upon a man who destroys them by a presentation of the facts as an enemy. I once knew a lady who became so attached to her family doctor that, she said, she would rather die under his treatment, if necessary, than to be cured by any other doctor. There are many people who are imbued with this kind of spirit not only in matters scientific, but in matters religious as well. Such people are not the kind who contribute to the world"s progress, but are the hindrances that have to be overcome.
CHAPTER VII.
ELECTRIC GENERATORS.
Of the sources of electricity we have mentioned two: Friction, and Galvanism or chemical action. There are hundreds of forms of the latter species of apparatus for generating electrical energy, so we will mention only a few of the more prominent ones. It is not our intention to go into the chemistry of batteries. There are too many exhaustive works on this subject lying on the shelves of libraries that are accessible to all. All galvanic batteries act on one general principle--the generation of electricity by the chemical action of acid on metal plates; but the chemistry of their action is very different. In all batteries the potential energy of one element is greater than the other. The acid of the battery dissolves the element of greater potentiality, and its energy is freed and under right conditions takes on the form of electricity. The potential of zinc, for instance, is greater than that of copper, and the measure of the difference is called the "electromotive force," the unit of which is the "volt."
Electromotive force is another name for pressure; the symbol for which is _E.M.F._
If we were to put two zinc plates in the battery fluid and connect them in the ordinary way there would be no electricity evolved (a.s.suming that they were perfectly h.o.m.ogeneous), because they are both of the same potential, or have the same possible amount of stored electrical energy measured by its working power. If one of the zinc plates were softer than the other, a feeble current would be developed, for one would be more readily acted upon by the acids than the other. The battery that has been most used in America for telegraphic purposes is called the gravity-battery. It is constructed by putting a copper plate in some form at the bottom of a jar, usually of gla.s.s, and filling it partly full of the crystals of sulphate of copper, commonly called "bluestone."
Zinc, usually cast in some open form, so as to expose a large surface to the solution, is suspended in the upper part of the jar, which is then filled with water till it covers the zinc. The zinc is the positive metal, but it is called the negative pole. The energy developed by the zinc pa.s.ses from zinc to copper and out on the circuit from the copper pole. Hence the copper came to be called the positive pole, although in relation to zinc it is negative. Copper would, however, be positive to some other metal whose potential was less. So you see that metals are relative, not absolute, in their character as positive and negative elements.
The galvanic battery has been almost entirely superseded in this country for telegraphic purposes by the dynamo, a machine developing electrical currents by mechanical power. Another form of battery that is extensively used for some kinds of heavy current work is called the storage-battery. The man who did the most, perhaps, to bring the storage-battery to its present state of perfection was Plante, a Frenchman, who died only a short time ago. Although very many types of battery have been developed, it is found that, after all, the lines on which he developed it make the most efficient battery. There is a common notion that electricity is stored in the storage-battery. Energy is stored, that will produce electricity when it is set free, just the same as energy is stored in zinc. The storage-battery, when ready for action, is one form of acid or primary battery. It has been made by pa.s.sing a current of electricity through it until the chemical relations of the two lead plates have been changed so that the potential of one is greater than that of the other. A simple storage-battery element is made up of two plates of lead held out of contact with each other by some insulating substance the same as the elements of an ordinary battery.
The cell is filled with dilute sulphuric acid, and there will be no electrical action till the cell has been charged by running a current of electricity through it and forming a lead oxide on one plate. Now, take off the charging battery and connect the two poles, and electricity will flow until the oxide has partly changed back into spongy metallic lead, when it must be renewed by recharging.
I remember perfectly well the first galvanic battery I ever saw, for it was of my own construction. It is now nearly fifty years ago, and yet it seems but yesterday--such is the flight of time. I related to you in another chapter how I made a voltaic battery--or pile, as it was called--by cutting up my mother"s boiler and her stove-zinc, and the domestic incident that followed. Well, a little later I made a real galvanic battery as follows: I lived in the country and far from town or city, and my facilities were extremely limited, so that I pursued my scientific investigations under great difficulties. My only text-book was an old Comstock"s Philosophy. In the book was a crude cut of a Morse register and a short description of its construction, including the battery. I determined to make a register, and I did. It was all constructed of wood except the magnet and its armature and the embossing-point, which latter was made of the end of a nail. The thing that seemed out of reach was the electromagnet. I had no money; and there was no one that believed I could do it, and if I could "what good would come of it?" I made friends with a blacksmith by keeping flies off a horse while he nailed the shoes on, and "blowing the bellows" and occasionally using the "sledge" for him. When I thought the obligation had acc.u.mulated a sufficient "voltage" (to express it electrically) I communicated to the blacksmith the situation and what I wanted.
The good-natured old fellow was not long in bending up a U magnet of soft iron and forging out an armature. The next step was to wind the U with insulated wire. The only thing that I had ever seen of the kind was an iron wire called "bonnet" wire that was wrapped with cotton thread.
This, however, was not available, so I captured a piece of bra.s.s bell-wire and wound strips of cotton cloth around it for insulation--and in that way completed the magnet.
Now everything was ready but the battery. I went at its construction with a feeling almost akin to awe, for I could not believe that it would do as described in the book. I procured a candy-jar from the grocer and found some pieces of sheet zinc and copper. These I rolled together into loose spirals and placed one inside the other so that they would not touch, when I was ready for the solution. The druggist trusted me for a half pound of "blue vitriol," and I put it into my battery and filled it with water. I waited awhile for it to dissolve, and then connected my magnet in circuit, when--to my astonishment and delight--it would lift a pound or more. It was a great triumph. I never have had one since that gave me the same satisfaction. But I had my triumph all to myself. I was still the same "tinker" (a name I had long carried), and a nuisance to be endured but not encouraged.
The dynamo is the form of generator now in general use where heavy currents of electricity are needed. It is aptly described by a writer in Modern Machinery, Mr. John A. Grier, as a thing that when "at rest is a lifeless piece of mechanism; in action it has a living spirit as full of mystery as the soul of man." This is a poetic way of describing it that conveys to the mind a sense of the power and beauty of natural law in action, that would not come from a mere recital of the cold scientific facts. The facts, however, are necessary: but let us draw from them all the poetry and all the practical lessons that we can as we go along; for it is this blending of the poetic with the practical that lends a charm to our every-day "grind," and lightens the load of many a weary hour.