of this Act-such as that given in this volume, should be in the hands of every mine inspector, mine-owner, mining engineer, and mining overseer, and should be easily accessible to every working miner in Great Britain. The clause in this last mining Act which forbids the employment in mines and collieries of boys under twelve years of age (instead of under ten, as formerly), unless boys above ten and under twelve who are able to read and write, and who attend school for not less than three hours a day for two days in each weck, comes into operation on July 1, 1861.

In closing, we can recommend Mr. Fowler's excellent work as a complete and perfect manual on "The Law Relating to Collieries and Colliers." Several of the chapters will be found to be valuable and useful to those not immediately interested in coal mines. The general rules which govern this kind of property, and the relations of the persons engaged in this pursuit, are applicable to similar kinds of property and to other trades. To those interested in real estate, to masters and servants generally, this work will be interesting and instructive. To the managers and overseers of coal and iron mines it is invaluable as a work of reference. Mining inspectors will lighten their own labours by encouraging its circulation.

ROYAL INSTITUTION OF GREAT
BRITAIN.

Friday, April 12, 1861.-William Robert Grove, Esq., M.A., Q.C., F.R.S., Vice-President, in the chair.

ON THE APPLICATION OF THE LAW OF THE CONSERVATION OF FORCE TO ORGANIC NATURE. BY PROFESSOR HELMHOLTZ, F.R.S.

THE most important progress in natural philosophy by which the present century is distinguished, has been the discovery of a general law which embraces and rules all the various branches of physics and chemistry. This law is of as much importance for the highest speculations on the nature of forces, as for immediate and practical questions in the construction of machines. This law at present is commonly known by the name of "the principle of conservation of force." It might be better perhaps to call it, with Mr. Rankine, "the conservation of energy," because it does not relate to that which we call commonly intensity of force; it does not mean that the intensity of the natural forces is constant; but it relates more to the whole amount of power which can be gained by any natural process, and by which a certain amount of work can be done. For example: if we apply this law to gravity, it does not mean, what is strictly and undoubtedly true, that the intensity of the gravity of any given body is the same as often as the body is brought back to the same distance from the centre of the earth. Or with regard to the other elementary forces of nature-for example, chemical force: when two chemical elements come together, so that they influence each other, either from a distance or by immediate contact, they will always exert the same force upon each other-the same force both in intensity and in its direction and in its quantity. This other law, indeed, is true; but it is not the same as the principle of conservation of force. We may express the meaning of the law of conservation of force by saying that every force of nature when it effects any alteration loses and exhausts its faculty to effect the same alteration a second time. But while, by every alteration in nature, that force which has been the cause of this alteration is exhausted, there is always another force which gains as much power of producing new alterations in nature as the first has lost. Although, therefore, it is the nature of all inorganic forces to become exhausted by their own working, the power of the whole system in which these alterations take place is neither exhausted nor increased in quantity, but only changed in form.

(The Lecturer illustrated the law by referring to examples; as gravity, elasticity, heat, chemical forces. He pointed out also its general application to all nature, to the sun, and planetary system, and the influence of the sun and moon, heat and light, upon earth.) Many English philosophers have been occupied with working out the consequences of this most general and important principle for the theory of heat, for the energy of the solar system, for the construction of machines. Mr. Grove showed that every force of nature is capable of bringing into action every other force of nature; Mr. Joule, of Manchester, began to search for the value of the mechanical equivalent of heat, and to prove its constancy, principally guided by the more practical interests of engineering. The first exposition of the

general principle was published in Germany by Mr. Mayer, of Heilbron, in the year 1842. Mr. Mayer was a medical man, and much interested in the solution of physiological questions, and he found out the principle of the conservation of force guided by these physiological questions. At the same time also I myself began to work on this subject. I published my researches a little later than Mr. Mayer, in 1845. Now, at first sight, it seems very remarkable and curious, that even physiologists should come to such a law. It appears more natural that it should be detected by natural philosophers or engineers, as it was in England; but there is, indeed, a close connection between both the fundamental questions of engineering and the fundamental questions of physiology with the conservation of force. For getting machines into motion it is always necessary to have motive-power, either in water, fuel, or living animal matter. The constructors of machines, instruments, watches, within the last century, who did not know the conservation of force, were induced to try if they could not keep a machine in motion without any expenditure for getting the motive-power. Many of them worked for a long time very industriously to find out such a machine which should give perpetual motion, and produce any mechanical work which they liked. They called such a machine a perpetual mover. They thought they had an example of such a machine in the body of every animal. There, indeed, motive-power seemed to be produced every day without the help of any external mechanical force. They were not aware that eating could be connected with the production of mechanical power. Food they believed was wanted only to restore the little damages in the machine, or to keep off friction, like the fat which made the axles of wheels to run smoothly. Now, at first, by the mathematicians of the last century, the so-called principle of the conservation of vis rira was detected, and it was shown that, by the action of the purely mechanical powers, it was not possible to construct a perpetual mover; but it remained still doubtful if it would not be possible to do so by the interposition of heat, or electricity, or chemical force. At last the general law of conservation of force was discovered, and stated, and established; and this law shows that also by the connection of mechanical powers with heat, with electricity, or with chemical force, no such machine can be constructed to give a perpetual motion, and to produce work from nothing.

We must consider the living bodies under the same point of view, and see how it stands with them. Now, if you compare the living body with a steam-engine, then you have the completest analogy. The living animals take in food that consists of inflammable substances, fat and the so-called hydrocarbons, as starch and sugar, and nitrogenous substances, as albumen, flesh, cheese, and so on. Living animals take in these inflammable substances and oxygen; the oxygen of the air, by respiration. Therefore, if you take, in the place of fat, starch, and sugar, coals or wood, and the oxygen of the air, you have the substances in the steam-engine. The living bodies give out carbonic acid and water; and then if we neglect very small quantities of more complicated matters which are too small to be reckoned here, they give up their nitrogen in the form of urea. Now, let us suppose that we take an animal on one day, and on any day afterwards; and let us suppose that this animal is of the same weight the first day and the second day, and that its body is composed quite in the same way on both days. During the time-the interval of timebetween these two days the animal has taken in food and oxygen, and has given out carbonic acid, water, and urea. Therefore, a certain quantity of inflammable substance, of nutriment, has combined with oxygen, and has produced nearly the same substances, the same combinations, which would be produced by burning the food in an open fire-at least, fat, sugar, starch, and so on; and those substances which contained no nitrogen would give us quite in the same way carbonic acid and water, if they are burnt in the open fire, as if they are burnt in the living body; only the oxidation in the living body goes on more slowly. The albuminous substances would give us the same substances, and also nitrogen, as if they were burnt in the fire. You may suppose, for making both cases equal, that the amount of urea which is produced in the body of the animal may be changed without any very great development of heat into carbonate of animonia, and carbonate of ammonia may be burnt, and gives nitrogen, water, and carbonic acid. The amount of heat which would be produced by burning urea into carbonic acid and nitrogen would be of no great value when compared with the great quantity of heat which is produced by burning the fat, the sugar, and the starch. Therefore, we can change a certain amount of food into carbonic acid, water, and nitrogen,

either by burning the whole in the open fire, or by giving it to living animals as food, and burning afterwards only the urea. In both cases we come to the same result.

Now, I have said that the conservation of force for chemical processes requires a fixed amount of mechanical work, or its equivalent, to be given out during this process; and the amount is exactly the same in whatever way the process may go on. And, therefore, we must conclude that by the animal as much work must be done, must be given out-the same equivalent of mechanical work-as by the chemical process of burning. Now, let us remark that the mechanical work which is spent by an animal, and which is given to the external world, consists, firstly, in heat; and, secondly, in real mechanical work. We have no other forms of work, or of equivalent of work, given out by living animals. If the animal is reposing, then the whole work must be given out in the form of heat; and, therefore, we must conclude that a reposing animal must produce as much heat as would be produced by burning its food. A small difference would remain for the urea; we must suppose that the urea produced by the animal is also burnt, and taken together with the heat immediately produced by the animal itself. Now, we have experiments made upon this subject by the French philosophers Dulong and Desprez. They found that these two quantities of heat-the one emitted by burning, the other by the living animal-are nearly identical; at least, so far as could be established at that time, and with those previous researches which existed at that time. The heat which is produced by burning the materials of the food is not quite known even now. We want to have researches on the heat produced by the more complicated combinations which are used as food. Dulong and Desprez have calculated the heat according to the theoretical supposition of Lavoisier-which supposition is nearly right, but not quite right-therefore there is a little doubt as to the amount of the heat, but experiments show that at least to the tenth part of that heat the quantities are really equal; and we may hope, if we have better researches on the heat produced by burning the food, that these quantities will also be more equal than they were found to be by Dulong and Desprez.

Now, if the body be not reposing, but if muscular exertion take place, then also mechanical work is done. The mechanical work is very different, according to the different kinds of muscular exertion. If we walk only on a plane surface, we must overpower the resistance of friction and the resistance of the air; but these resistances are not so great that the work which we do by walking on a plane is of great amount. Our muscles can do work in very different ways. By the researches of Mr. Redtenbacher, the director of the Polytechnic School of Carlsruhe, it is proved that the best method of getting the greatest amount of work from a human body is by the treadmill-that is, by going up a declivity. If we go up the declivity of a hill we raise the weight of our own body. In the treadmill the same work is done, only the mill goes always down, and the man on the mill remains in his place.

Now, we have researches on the amount of air which is taken in, and of carbonic acid given out, during such work in the treadmill, made by Dr. Edward Smith. He found that a most astonishing increase of respiration takes place during such work. Now, you all know that if you go up a hill you are hindered in going too fast by the great frequency and the great difficulty of respiration. This, then, becomes far greater than by the greatest exertion of walking on a plain, and really the difficulty is produced by the great mechanical work which is done in the same time. Now, partly from the experiments of Dulong and Desprez, and partly from the experiments of Dr. Edward Smith, we can calculate that the human body, if it be in a reposing state, but not sleeping, consumes so much oxygen, and burns so much carbon and hydrogen, that during one hour so much heat is produced that the whole body, or a weight of water equal to the weight of the body, would be raised in temperature one degree and two-tenths centigrade (two degrees and two-tenths Fahrenheit). Now, Dr. Edward Smith found that by going in the treadmill at such a rate that if he went up a hill at the same rate he would have risen during one hour 1,712 feet, that during such a motion he exhaled five times as much carbonic acid as in the quiet state, and ten times as much as in sleeping. Therefore the amount of respiration was increased in a most remarkable way. If we now calculate these numbers, we find that the quantity of heat which is produced during one hour of repose is one degree and two-tenths centigrade, and that these are nearly equivalent to rising 1,712 feet, so that, therefore, the amount of mechanical work done in a treadmill, or done in ascending a hill at a

good rate, is equivalent to the whole amount of heat must be given up if there is complete conservation of which is produced in a quiescent state. The whole force. amount of the decomposition in the living body is five There may be other agents acting in the living times as great as in a reposing and wakeful state. Of body than those agents which act in the inorganic these five quantities, one quantity is spent for mecha-world; but those forces, as far as they cause chemical nical work, and four-fifths remain in the form of heat. and mechanical influences in the body, must be quite Always in ascending a hill, or in doing great mecha- of the same character as inorganic forces, in this at nical work, you become hot, and the production of least, that their effects must be ruled by necessity, heat is extremely great, as you well know, without and must be always the same, when acting in the making particular experiments. Hence you see how same conditions, and that there cannot exist any much the decomposition in the body is increased by arbitrary choice in the direction of their actions. doing really mechanical work. This is that fundamental principle of physiology mentioned in the beginning of this discourse. Still at the beginning of this century physiologis s believed that it was the vital principle which caused the processes of life, and that it detracted from the dignity and nature of life, if anybody expressed his belief that the blood was driven through the vessels by the mechanical action of the heart, or that respiration took place according to the common laws of the diffusion of gases.

Now, these measurements give us another analogy. We see that in ascending a mountain we produce heat and mechanical work, and that the fifth part of the equivalent of the work which is produced by the chemical process is really gained as mechanical work. Now, if we take our steam engine, or a hot-air engine, or any other engine which is driven by heat in such a way that one body is heated and expands, and by the expansion other bodies are moved,-I say, if we take any thermo-dynamic engine, we find that the greatest The present generation, on the contrary, is hard at amount of mechanical work which can be gained by work to find out the real causes of the processes which chemical decomposition or chemical combination is go on in the living body. They do not suppose that only an eighth part of the equivalent of the chemical there is any other difference between the chemical and force, and seven-eighths of the whole are lost in the the mechanical actions in the living body, and out of form of heat; and this amount of mechanical work it, than can be explained by the more complicated can only be gained if we have the greatest difference circumstances and conditions under which these actions of temperature which can be produced in such a take place; and we have seen that the law of the conmachine. In the living body we have no great differ-servation of force legitimizes this supposition. This ence of temperature; and in the living body the law, moreover, shows the way in which this fundaamount of mechanical work which could be gained if mental question, which has excited so many theoretical the living body were a thermo-dynamic engine, like speculations, can be really and completely solved by the steam-engine or the hot-air engine, would be much experiment. smaller than one-eighth. Really, we find from the great amount of work done, that the human body is in this way a better machine than the steam-engine,

only its fuel is more expensive than the fuel of steamengines.

There is another machine which changes chemical force into mechanical power-that is, the magnetoelectric machine. By these magneto-electric machines a greater amount of electrical power can be changed into mechanical work than in our artificial thermodynamic machines. We produce an electric current by dissolving zinc in sulphuric acid, and liberating another oxidizable matter. Generally it is only the difference of the attraction of zinc for oxygen compared with the attraction of copper or nitrous acid for oxygen. In the human body we burn substances which contain carbon and hydrogen, and therefore the whole amount of attraction of carbon and hydrogen for oxygen is put into action to move the machine; and in this way the power of the living body is greater and more advantageous than the power of the mag

neto-electric machine.

Let us now consider what consequences must be drawn when we find that the laws of animal life agree

with the law of the conservation of force, at least as far as we can judge at present regarding this subject. As yet we cannot prove that the work produced by living bodies is an exact equivalent of the chemical forces which have been set into action. It is not yet possible to determine the exact value of either of these quantities so accurately as will be done ultimately; but we may hope that at no distant time it may be possible to determine this with greater accuracy. There is no difficulty opposed to this task. Even at present I think we may consider it as extremely pro

bable that the law of the conservation of force holds good for living bodies.

Now, we may ask, what follows from this fact as regards the nature of the forces which act in the living body?

The majority of the physiologists in the last century, and in the beginning of this century, were of opinion that the processes in living bodies were determined by one principal agent, which they chose to call the "vital principle." The physical forces in the living body they supposed could be suspended or again set free at any moment, by the influence of the vital principle; and that by this means this agent could produce changes in the interior of the body, so that the health of the body would be thereby preserved or restored.

MR. E. REEVES, M.D., in a letter addressed to the Herald, Melbourne, states that liquid quartz, glass, or flint, is easily prepared by fusing together in an iron ladle in the heat of a smith's forge 14 pints of powdered quartz and 1 of pearl ash (dry) until they form a glass, which, when cool, should be powdered and boiled with four pints of water, in an iron pot, for four hours, or until dissolved. Water should be added from time to time to keep up the quantity, and when all the powder is dissolved the liquid should be boiled until it is of the consistence of thin treacle, and then, as soon as cool enough, bottled. It can be thinned by the addition of water. For indoor usefor giving a coating of glass to wood or paint, or the paper of rooms, or paper boxes-it is equal to the finest varnish, and several hundred per cent. cheaper. It may be used alone, but for ceilings and walls, either whitewashed or colour washed, the wash should be applied and allowed to dry, then apply the liquid glass (one pint to three of water) with a clean wash brush. This last plan also answers well for wooden houses, wooden roofs, or for stone houses, the lime of the whiting and the glass uniting and forming an enamel which will bear to be washed with boiling water. Wood or stone work, or any other material which it is not desirable to colour, should be washed (with a wash brush) with the liquid glass (one part to three of water), and then while wet with a solution of sal-ammoniac (lb. to a gallon of water). Wood intended to be exposed in water or underground (the more porous it is the better) should be first steeped until thoroughly saturated in the sal-ammoniac solution, and then placed in the liquid glass (one pint to six of water), and allowed to remain for several days. This would effectually protect railway sleepers, the piles of wharves, ships' bottoms, and give the pine, of which so many ships are built, a durability beyond that of the best oak. Iron and other metals can be effectually protected from the action of sea water and the atmosphere, by a coating of this liquid glass. If the wire of a telegraph cable was placed in the centre of an untarred hempen cable, and the cable passed through the liquid glass, and then through the solution of sal-ammonia, it would be effectually protected from the action of the sea-water, It would be, perhaps, advisable to envelope the wire in india-rubber or gutta-percha-although the elastic glass tube which the cable would form around it would form an effectual protection from the action of the seawater. The saturation with the liquids should be done just before or at the time the cable is being paid out; the sea-water would assist in solidifying the glass in the hemp.

Now, the conservation of force can exist only in those systems in which the forces in action (like all forces of inorganic nature) have always the same AN Amateur Photographic Association has been intensity and direction if the circumstances under organized, having for its object the interchange and which they act are the same. If it were possible to publication of the productions of amateur photodeprive any body of its gravity, and afterwards to graphers. The subscription is only one guinea per restore its gravity, then indeed we should have the annum. Messrs. M'Lean, Melhuish, Napper, and Co., perpetual motion. Let the weight come down as long 26, Haymarket, are the printers and publishers, and as it is heavy; let it rise if its gravity is lost; then Mr. Arthur James Melhuish, honorary secretary. you have produced mechanical work from nothing. This association is expected to prove for amateur phoTherefore this opinion that the chemical or mecha- tographers an "Exchange Club" of the most comnical power of the elements can be suspended, or prehensive kind, a bond of union, a medium of comchanged, or removed in the interior of the living body,munication, and means of mutual improvement.

TOOTH'S MACHINERY FOR THE MANUFACTURE OF IRON AND STEEL. WE have had to revert, on more than one occasion, to the invention of Mr. W. H. Tooth for the manufacture of iron and steel, and have now great pleasure in laying before our readers illustrations of the machinery and a full explanation of the method he employs in such manufacture.

This invention of improved machinery to be emiron and steel, and of puddled steel and wrought ployed in the manufacture, melting, or refining of iron, relates to a novel construction of apparatus, in which the iron or material to be operated upon is placed in a horizontal rotating cylinder or barrel, into which is directed the flame and heated gases from a furnace placed at one end of the rotating cylinder. The rotating cylinder is mounted upon rollers or rails or suspended by chains, and rotary motion is communicated to it by suitable gearing, so that the materials inside may roll over and over as the cylinder rotates. The furnace is mounted on a moveable frame, so that it may, when required, be moved away from the rotating cylinder, or, if preferred, it may be stationary, and the rotating cylinder be mounted on a moveable frame or turntable, so that it may be turned round or moved away for the convenience of charging and discharging or for repairs. The flame and gases from the furnace are directed into the rotating cylinder, where they will act upon the iron or materials placed therein, and, after so doing, the gases will pass out at the opposite end of the cylinder into the flue or chimney, which may be provided with a damper or other suitable contrivance for regulating the draught.

It will be necessary that the entrance to the rotating cylinder from the fireplace should be much larger than the exit aperture into the flue, to prevent the heat from passing too quickly into the flue. By this means the heat will be kept in the rotating cylinder, and by making the opening into the cylinder of large dimensions the workman will also be enabled to get out the charge with facility. The moveable furnace is adapted to the rotating chambers in such a manner as to admit of atmospheric air being allowed, when required, to enter all round the joint between the moveable fireplace and the rotating cylinder, so that the air, by commingling with the combustible gases, will greatly increase the heat in the rotating cylinder by promoting the combustion of the gases that are directed from the furnace into the rotating cylinder. Sometimes, for greater convenience, the inventor finds it advisable to construct the exit flues at the opposite end of the rotating cylinder in such a manner as to cause the gases to descend when they pass out of the cylinder, or to pass to the right or left; and, in order to utilize the heat that passes into the flue from the rotating chamber or cylinder, the gases are caused to enter a chamber, in which the metal for the next charge is placed, so that previous to will become heated by the waste gases which are being placed in the rotating chamber the charge passing to the flue. That part of the flue which is nearest the exit aperture of the rotating cylinder is sometimes provided with a moveable cap or cover for the convenience of charging and discharging the rotating cylinder.

The rotating cylinder is, by preference, to be constructed of sheet iron, which, if thought desirable, may be perforated or made hollow at some parts, for the purpose of allowing a circulation of air, whereby the framing will be kept cool. The cylinder is to be lined with fire-stone or clay, or other material or composition that will vitrify or glaze by the application of heat, and will therefore be able to resist the action of molten metal. The rotating cylinder is mounted on antifriction rollers, and is made to rotate horizontally, and its inner side or lining is parallel to the axis, so that as the cylinder rotates the contents will roll over and over, but will not be moved laterally or from side to side. By the rotation of the cylinder the molten iron will be agitated under the covering layer of cinder, and the decarbonization of the metal will take place without any deleterious amount of oxydation taking place at the same time, as is now the case. The bricks or stones, or some of them, may be made hollow, as shown in the sectional views,

be left open and exposed, in order that the interior may be more accessible when it is required to introduce

or remove a shaft or

forging. In fig. 1 the part g of the exit flue is represented as mounted on rollers, which are arranged to run on rails. For some purposes, however, it will be found more convenient to make the fireplace d and exit flue and chamber g stationary, and to place the rotating cylinder a on a moveable frame or platform, which is made to turn on a central pivot somewhat like a railway turntable, the platform being supported from below by rollers. When this

arrangement of parts is adopted the faces of the mouthpieces at each end of the rotating cylinder must be curved according to the radius from the central vertical turning point of the platform of the rotating cylinder. It will now be understood that by simply turning the platform one-quarter round, the axis of the rotating cylinder will be brought at right angles to a line passing through the fireplace, the rotating cylinder, and the exit flue, when all the parts are in their working position, and consequently access may then be easily obtained to the interior of the rotating cylinder.

In puddling iron in this apparatus it will be found desirable occasionally to admit a regulated supply of atmospheric air in the rotating cylinder to commingle with the combustible gases therein; this object is effected by so arranging and constructing the fireplace d that it may be drawn back slightly from the mouthpiece or entrance to the rotating cylinder, so that by admitting a thin stream or film of atmospheric air at the point where these gases are entering the rotating cylinder, the air may be made to intimately commingle with the gases, and the combustion of the latter may be completely effected. Air, to support combustion in the fireplace d, and to form a blast to carry the gases into the rotating cylinder a, is forced into the fireplace by a fan or blower, and is admitted either under the fire-bars or direct into the body of the fuel.

Proceedings of Societies.

SOCIETY OF ARTS.
May 22nd.

ON A NEW METHOD OF PRODUCING ON GLASS, PHOTOGRAPHS OR OTHER PICTURES, IN ENAMEL COLOURS. BY F. JOUBERT.

Or all the inventions to which the genius of man has given birth, and which have been progressively developed and brought, by his industry, to a high degree of perfection and usefulness, the art of glassmaking is certainly one of the most interesting and extraordinary. At the same time it is doubtless one which has tended to increase our comforts and our enjoyments in a degree almost unequalled by any other discovery of modern civilization.

If we look back to the dark ages, and find that in those days even the rulers of the earth had no means of keeping rain and bad weather from their habitations, except by also shutting out the light, we shall be ready to acknowledge the astonishing results, as compared with the present state of things around us, which the persevering efforts of man have, under the guidance of an ever-merciful Providence, been able to accomplish.

THE HISTORY OF GLASS AND GLASS PAINTING.

We have no distinct evidence to show what nation first used glass, and we must therefore be satisfied with the various traditions transmitted to us, from age to age, on the subject. One fact, however, seems established beyond the possibility of a doubt, viz., that the greatest antiquity can be assigned to this invention, since the Egyptians and the Phenicians had both vessels and ornaments made of glass, crude in form, but of a substance so perfect, by whatever means obtained, that it has stood the trial of several thousand years, and may be pronounced to have

suffered no deterioration.

But still more remote is the mention of glass in the Holy Scripture; for, if the interpretation of the text be a correct one, in the 18th chapter of Job, as also in

several other parts of the Bible, is found an allusion to a substance which we imagine must have been glass. Next to this, Alexander Aphrodisius amongst the ancient Greeks, Lucretius, Flavius Vopiscus, and other Latin authors, have left us a correct description of glass. Aristophanes also alludes to glass in one of his plays, and Aristotle brings out two problems on the subject; the first, why is it we see through glass? the second, why can we not bend glass?

Admitting that these two propositions emanate from the celebrated philosopher, they appear to give conclusive evidence that glass was familiar to the Greeks.

But we may, perhaps, even trace the origin of this invention far earlier, and to the remotest period of the existence of man, by associating it with the art of making bricks, which was, it is believed, practised by the earliest inhabitants of the north; and it is not difficult to imagine how such an art would originate. Man was led, for his subsistence, to seek a mode of preparing animal food for his use by roasting it over the fire, and having, in course of time, built, rudely, a sort of oven made of earth, and the earth having become hardened through the action of the fire, our forefathers would soon discover all the advantages which might be derived from such a process for making bricks or pots, and utensils for common use. Specimens of the potter's art in ancient times we have plenty, and in a variety of forms or shapes, which for elegance have not been surpassed. We need only allude to the Etruscan vases in the collection of the British Museum.

In firing bricks it will not unfrequently happen that some kind of vitrification takes place in the bricks placed in the most violent part of the fire, and one might naturally suppose that one process would lead to the other; but such does not appear to have been the case, at any rate, for many centuries. Later, horn and skins were in use down to the third or fourth centuries of the Christian era, and oiled paper or mica were also used in lieu of window glass, nearly up to the time of the reign of Elizabeth. If we are to give credence to the narrative of Pliny, to accident

alone, as in many other instances, we should be indebted for the discovery of glass: Some traders, being weather-bound, landed on the banks of a river in Syria, and began to dispose a place in the sand for cooking their meals, after having gathered for fuel a great quantity of an herb, known there by the name of kali, which plant must have contained a large proportion of carbonate of soda, and this being mixed with the sand, yielded, through the agency of the fire,

a sort of vitreous substance. Such is one of the accredited versions of the origin of glass.

Glass has at all times. until recently, been thought a substance of great importance, and even amongst the primitive inhabitants of South America and of the Indian continent, who were, when first visited by the early European navigators, found to possess gold and silver ornaments in abundance, it is well known that the first discoverers of those countries who happened to land in search of food or for water, had no difficulty in obtaining from the natives gold in exchange for some valueless pieces of glass, or a few glass beads, which they would immediately use as an ornament round their neck or their wrist. As late as the middle of the last century, glass beads of various descriptions, and of all sorts of colours, were extensively manufactured in France, principally for exportation to the colonies of South America and the islands of the

Pacific Ocean.

It appears that, although vessels made of glass had been in use for a considerable time previously, it is only about the third century of our era that glass began to be used for glazing windows. These consisted in an infinite number of small panes of various shapes, which were arranged so as to form certain designs for the ornamenting of windows in places of worship; glass having, on account of its rarity then, been almost, if not entirely, confined to that use.

St.

St. Jerome, who wrote in the fourth century, speaks of glass in church windows; and Gregoire de Tours relates, two hundred years later, in the year 525, that which had invaded Auvergne, entered into a church a soldier of the army of the King of the Visigoths, through a window, of which he broke the glass. Fortunat, Bishop of Poictiers, towards the end of the seventh century, describes with admiration the painted windows of the Cathedral of Paris. Philibert, also in the seventh century, had the windows of the celebrated Abbey of Jumuges, on the banks of the Seine, near Rouen, decorated with glass. unknown in England, and it was Wilfrid, Bishop of In the beginning of the eighth century glass was York, who died in 709, who first introduced glass into England, by sending for some glass-makers from France, according to a record kept to this day. A few years later, St. Bennet, Abbot of Wearmouth, wishing to decorate the windows of his monastery, sent for some glass-makers, also from France; for it appears, from some authentic records, that the art of decorating windows with glass was practised in several parts of France, especially in Normandy, long before it became adopted by other countries.

It would seem that the art of staining glass was very early discovered, although no date can be correctly assigned to the period when stained glass for church windows was first used. The practice generally adopted was to make a sort of mosaïque design, by placing an infinite number of small pieces of coloured glass together. This was in use for several centuries before the art of painting on glass, properly speaking, was discovered, which seems to have soon extensively spread and was cultivated by many excellent artists, if we may judge from the numerous specimens yet in existence on the continent. But to the sixteenth century, so rich already in artistical talent, was reserved the glory of carrying glass painting to a degree of excellence which has never been equalled since; and the names of Jean Cousin and Bernard de Palissy will be honoured for ever, amongst the large phalanx of glass painters in all countries. The most remarkable, perhaps, of painted painted windows in this coutry, are the windows of the various colleges at Oxford, which were executed during the seventeenth century by Bernard Van Linge and his pupils. William Price also repaired some of the glass paintings in Queen's College, Oxford, and in Christ Church painted a remarkable composition from the designs of Sir James Thornhill. Besides these may be mentioned the windows of Lichfield Cathedral, and several other very ancient windows in Christ Church College, and especially in the residence of the Dean of Westminster, near the Abbey.

Having been, for many years, professionally acquainted with printing in connection with the fine arts, and having observed the immense development the new art of photography has taken, and the large field it has opened for representing all sorts of subjectsof animated as well as still life-it occurred to me