Heroes of Science: Physicists Part 9

Lady Thompson lived to hear of her husband's high position in Bavaria, but died on January 29, 1792. When Rumford came to London in 1795, he wrote to his daughter, who was then twenty-one years of age, to meet him there, and on January 29, 1796, she started in the _Charlestown_, from Boston. She remained with her father for more than three years, and her autobiography gives much information respecting the count's doings during this time.

While in London, Count Rumford attained a high reputation as a curer of smoky chimneys. One firm of builders found full employment in carrying out work in accordance with his instructions; and in his hotel at Pall Mall he conducted experiments on fireplaces. He concluded that the sides of a fireplace ought to make an angle of 135 with the back, so as to throw the heat straight to the front; and that the width of the back should be one-third of that of the front opening, and be carried up perpendicularly till it joins the breast.

The "Rumford roaster" gained a reputation not less than that earned by his open fireplace.

It was during this stay in London that Rumford presented to the Royal Society of London, and to the American Academy of Sciences 1000 Three per Cent. Stock, for the purpose of endowing a medal to be called the Rumford Medal, and to be given each alternate year for the best work done during the preceding two years in the subjects of heat and light.

He directed that two medals, one in gold and the other in silver, should be struck from the same die, the value of the two together to amount to 60. Whenever no award was made, the interest was to be added to the princ.i.p.al, and the excess of the income for two years over 60 was to be presented in cash to the recipient of the medal. At present the amount thus presented is sufficient to pay the composition fee for life members.h.i.+p of the Royal Society. The first award of the medal was made in 1802, to Rumford himself. The other recipients have been John Leslie, William Murdock, etienne-Louis Malus, William Charles Wells, Humphry Davy, David Brewster, Augustin Jean Fresnel, Macedonio Melloni, James David Forbes, Jean Baptiste Biot, Henry Fox Talbot, Michael Faraday, M. Regnault, F. J. D. Arago, George Gabriel Stokes, Neil Arnott, M. Pasteur, M. Jamin, James Clerk Maxwell, Kirchoff, John Tyndall, A. H. L. Fizeau, Balfour Stewart, A. O. des Cloiseaux, A. J. ngstrom, J. Norman Lockyer, P. J. C. Janssen, W.

Huggins, Captain Abney.

In the summer of 1796 Rumford and his daughter left England to return to Munich. On account of the war, they were obliged to go by sea to Hamburg; whence they drove to Munich, where the count was anxiously expected, political troubles having compelled the elector to leave the city. After the battle of Friedburg, the Austrians retired to Munich, and, finding the gates of the city closed, they fortified themselves on an eminence overlooking the city, and, through some misunderstanding with the local authorities, the Austrian general threatened to attack the city if any Frenchman should be allowed to enter. Rumford took supreme command of the Bavarian forces, and so gained the respect of the rival generals that neither the French nor the Austrians made any attempt to enter the city. The large number of soldiers now in Munich gave Rumford a good opportunity to exercise his skill in cooking on a large scale, and this he did, adding to the comfort of the soldiers and reducing the cost of the commissariat. On the return of the elector, Miss Sarah was made a countess, and one-half of her father's pension was secured to her, thus providing her with an income of about 200 per annum for life. Many of the details of the home life and social intercourse during this period of residence at Munich are preserved in the autobiography of the countess, as well as accounts of excursions, including a trip by river to Salzburg for the purpose of inspecting the salt-mines. After two years' stay in Munich, the count was appointed Minister Plenipotentiary from Bavaria to the Court of Great Britain. After an unpleasant and perilous journey, he reached London, _via_ Hamburg, in September, 1798, but was terribly disappointed on learning that a British subject could not be accepted as an envoy from a Foreign Power. As he did not then wish to return to Bavaria, he purchased a house in Brompton Row. But he had been too much accustomed to great enterprises to be content with a quiet life, and was bound to have some important scheme on hand. Pressing invitations were sent him to return to America, but he preferred residence in London, and devoted himself to the foundation of the Royal Inst.i.tution, though the countess returned to the States in August, 1799. A letter from Colonel Baldwin to her father shortly after her return contains the following pa.s.sage:--

In the cask of fruit which your daughter and Mr. Rolfe have sent you, there is half a dozen apples of the growth of my farm, wrapped up in papers, with the name of _Baldwin's apples_ written upon them.... It is (I believe) a spontaneous production of this country; that is, it was not originally engrafted fruit.

The history of the remaining period of Rumford's residence in London is the early history of the Royal Inst.i.tution.

For many years Rumford had had at his disposal for his philanthropic projects all the resources of the electorate of Bavaria, and he had done everything on a royal scale. His original plan for the Royal Inst.i.tution appears to embody to a very great extent the work of the Science and Art Department, the City and Guilds Inst.i.tute for the Advancement of Technical Education, the National School of Cookery, the London Society for the Extension of University Teaching, and, in addition to all this, to have comprehended a sort of perpetual International Health Exhibition, where every device for domestic purposes, and especially for the improvement of the condition of the poor, could be inspected. How all this was to be carried out with the resources which the count expected to be able to devote to the purpose, does not appear. Foremost among the objects of the inst.i.tution was placed the management of fire; for its promoter was convinced that more than half the fuel consumed in the country might be saved by proper arrangements.

The philanthropic objects with which the inst.i.tution was started are apparent from the fact that it was the Society for Bettering the Condition of the Poor which appointed a committee to confer with Rumford, to report on the scheme, and to raise the funds necessary for starting the project; and one of Rumford's hopes in connection with it was "to make benevolence fas.h.i.+onable." It was arranged that donors of fifty guineas each should be perpetual proprietors of the inst.i.tution; and that subscribers should be admitted at a subscription of two guineas per annum, or ten guineas for life. The price of a proprietor's share was raised to sixty guineas from May 1, 1800, and afterwards increased by ten guineas per annum up to one hundred guineas. In a very short time there were fifty-eight fifty-guinea subscribers, and to them Rumford addressed a pamphlet, setting forth his scheme in detail. The following are specified as some of the contents of the future inst.i.tution:--"Cottage fireplaces and kitchen utensils for cottagers; a farm-house kitchen with its furnis.h.i.+ngs; a complete kitchen, with its utensils, for the house of a gentleman of fortune; a laundry, including boilers, was.h.i.+ng, ironing, and drying rooms, for a gentleman's house, or for a public hospital; the most improved German, Swedish, and Russian stoves for heating rooms and pa.s.sages." As far as possible all these things were to be seen at work. There were also to be ornamental open stoves with fires in them; working models of steam-engines, of brewers' boilers, of distillers'

coppers and condensers, of large boilers for hospital kitchens, and of s.h.i.+ps' coppers with the requisite utensils; models of ventilating apparatus, spinning-wheels and looms "adapted to the circ.u.mstances of the poor;" models of agricultural machinery and bridges, and "of all such other machines and useful instruments as the managers of the inst.i.tution shall deem worthy of public notice." All articles were to be provided with proper descriptions, with the name and address of the maker, and the price.

A lecture-room and laboratory were to be fitted up with all necessary philosophical apparatus, and the most eminent expounders of science were to be engaged for the purpose of "teaching the application of science to the useful purposes of life."

The lectures were to include warming and ventilation, the preservation of food, agricultural chemistry, the chemistry of digestion, of tanning, of bleaching and dyeing, "and, in general, of all the mechanical arts as they apply to the various branches of manufacture."

The inst.i.tution was to be governed by nine managers, of whom three were to be elected each year by the proprietors; and there was also to be a committee of visitors, the members of which should not be the managers. The king became patron of the inst.i.tution, and the first set of officers was nominated by him. The Earl of Winchelsea and Nottingham was President; the Earls of Morton and of Egremont and Sir Joseph Banks, Vice-Presidents; the Earls of Bessborough, of Egremont, and of Morton, and Count Rumford, were among the Managers; the Duke of Bridgewater, Viscount Palmerston, and Earl Spencer the Visitors; and Dr. Thomas Garnett was appointed first Professor of Physics and Chemistry. The royal charter of the inst.i.tution was sealed on January 13, 1800. The superintendence of the journals of the inst.i.tution was entrusted to Rumford's care. For some time the count resided in the house in Albemarle Street, which had been purchased by the inst.i.tution, and while there he superintended the workmen and servants.

Dr. Thomas Garnett, the first professor at the inst.i.tution, was highly respected both as a man and a philosopher, and seems to have been everywhere well spoken of. But Rumford and he could not work together, and his connection with the inst.i.tution was consequently a short one.

Rumford was then authorized to engage Dr. Young as Professor of Natural Philosophy, editor of the journals, and general superintendent of the house, at a salary of 300 per annum. Shortly before this the count's attention had been directed to the experiments on heat, made by Humphry Davy, and on February 16, 1801, it was "resolved that Mr.

Humphry Davy be engaged in the service of the Royal Inst.i.tution, in the capacity of a.s.sistant-Lecturer in Chemistry, Director of the Chemical Laboratory, and a.s.sistant-Editor of the Journals of the Inst.i.tution; and that he be allowed to occupy a room in the house, and be furnished with coals and candles, and that he be paid a salary of one hundred guineas _per annum_." In his personal appearance, Davy is said to have been at first somewhat uncouth, and the count was by no means charmed with him at their first interview. It was not till he had heard him lecture in private that Rumford would allow Davy to lecture in the theatre of the inst.i.tution; but he afterwards showed his complete confidence in the young chemist by ordering that all the resources of the inst.i.tution should be at his service. Davy dined with Rumford at the count's house in Auteuil, when he visited Paris with Lady Davy and Faraday, in 1813. He commenced his duties at the inst.i.tution on March 11, 1801. It was on June 15, in the same year, that the managers having objected to the syllabus of his lectures, Dr.

Garnett's resignation was accepted; and on July 6 Dr. Young was appointed in his stead. Dr. Young resigned after holding the appointment only two years, as he found the duties incompatible with his work as a physician.

Rumford's life in London now became daily more unpleasant to himself.

Accustomed, as he had been in Bavaria, to carry out all his projects "like an emperor," it was difficult for him to work as one member of a body of managers. One by one he quarrelled with his colleagues, and at length left England, in May, 1802, never to return.

When distinguished men of science are placed at the head of an inst.i.tution like that which Rumford founded, there is always a tendency for the _technical_ teaching of the establishment to become gradually merged into scientific research; and in this case, after Rumford's departure, the genius of Davy gradually converted the Royal Inst.i.tution into the establishment for scientific research which it has been for more than three quarters of a century. Probably the man who has come nearest to realizing all that Count Rumford had planned for his inst.i.tution is the late Sir Henry Cole; but he succeeded only through the resources of the Treasury.

On leaving England in May, 1802, Rumford went to Paris, where he stayed till July or August, when he revisited Bavaria and remained there till the following year, when he returned to Paris. He was again at Munich in 1805; but under the new elector, though an old friend of the count, relations.h.i.+ps do not seem to have been all that they were with his uncle, and at length the elector himself was compelled to leave Munich, and soon after the Bavarian sovereign became a va.s.sal of Napoleon. On October 24, 1805, Rumford married Madame Lavoisier, a lady of brilliant talents and ample fortune. That his position might be nearly equal to hers, the Elector of Bavaria raised his pension to 1200 per annum. A house, Rue d'Anjou, No. 39, was purchased for six thousand guineas, and Rumford expended much thought and energy in making it, with its garden of two acres, all that he could desire. But the union was not so happy as he antic.i.p.ated. The count loved quiet; Madame de Rumford was fond of company: to the former the pleasure of the table had no charms; the latter took delight in sumptuous dinner-parties. As time went on, domestic affairs became more and more unpleasant, and at length a friendly separation was agreed upon, after they had lived together for about three years and a half. The count then retired to a small estate which he hired at Auteuil, about four miles from Paris. The Elector of Bavaria was crowned king on January 1, 1806, and in 1810 Rumford was again at Munich, for the purpose of forming, at the king's request, an Academy of Arts and Sciences. At Auteuil the count was joined by his daughter in December, 1811, her journey having been much delayed through the capture of the vessel in which she had taken her pa.s.sage, off Bordeaux. An engraving of the house at Auteuil, and the room in which Rumford carried on his experiments, was published in the _Ill.u.s.trated London News_ of January 22, 1870.

While resident at Auteuil, Rumford frequently read papers before the Inst.i.tute of France, of which he was a member. He complained very much of the jealousy exhibited by the other members with reference to any discoveries made by a foreigner. He died in his house at Auteuil, on August 21, 1814, in the sixty-second year of his age. In 1804 he had made over, by deed of gift to his mother, the sum of ten thousand dollars, that she might leave it by will to her younger children. As before mentioned, Harvard College was his residuary legatee, and the property so bequeathed founded the Rumford Professors.h.i.+p in that inst.i.tution.

Cuvier, as Secretary of the Inst.i.tute, p.r.o.nounced the customary eulogy over its late member. The following pa.s.sages throw some light on the reputation in which the count was held:--

He has constructed two singularly ingenious instruments of his own contriving. One is a new calorimeter for measuring the amount of heat produced by the combustion of any body. It is a receptacle containing a given quant.i.ty of water, through which pa.s.ses, by a serpentine tube, the product of the combustion; and the heat that is generated is transmitted through the water, which, being raised by a fixed number of degrees, serves as the basis of the calculations. The manner in which the exterior heat is prevented from affecting the experiment is very simple and very ingenious. He begins the operation at a certain number of degrees below the outside heat, and terminates it at the same number of degrees above it. The external air takes back during the second half of the experiment exactly what it gave up during the first. The other instrument serves for noting the most trifling differences in the temperature of bodies, or in the rapidity of its changes. It consists of two gla.s.s bulbs filled with air, united by a tube, in the middle of which is a pellet of coloured spirits of wine; the slightest increase of heat in one of the bulbs drives the pellet towards the other. This instrument, which he called a thermoscope, was of especial service in making known to him the varied and powerful influence of different surfaces in the transmission of heat, and also for indicating a variety of methods for r.e.t.a.r.ding or hastening at will the processes of heating and freezing....

He thought it was not wise or good to entrust to men, in the ma.s.s, the care of their own well-being. The right, which seems so natural to them, of judging whether they are wisely governed, appeared to him to be a fict.i.tious fancy born of false notions of enlightenment. His views of slavery were nearly the same as those of a plantation-owner. He regarded the government of China as coming nearest to perfection, because, in giving over the people to the absolute control of their only intelligent men, and in lifting each of those who belonged to this hierarchy on the scale according to the degree of his intelligence, it made, so to speak, so many millions of arms the pa.s.sive organs of the will of a few sound heads--a notion which I state without pretending in the slightest degree to approve it, and which, as we know, would be poorly calculated to find prevalence among European nations.

As for the rest, whatever were the sentiments of M. Rumford for men, they in no way lessened his reverence for G.o.d. He never omitted any opportunity in his works of expressing his religious admiration of Providence, and of proposing for that admiration by others, the innumerable and varied provisions which are made for the preservation of all creatures; indeed, even his political views came from his firm persuasion that princes ought to imitate Providence in this respect by taking charge of us without being amenable to us.

In front of the new Government offices and the National Museum in the Maximilian Stra.s.se, in Munich, stand, on granite pedestals, four bronze figures, ten feet in height. These represent General Deroy, Fraunhofer, Sch.e.l.ling, and Count Rumford. The statue of Rumford was erected in 1867, at the king's private expense. In the English garden which Rumford planned and laid out is the monument erected during his absence in England in 1796, and bearing allegorical figures of Peace and Plenty, and a medallion of the count.

The bare enumeration of Rumford's published papers would occupy considerable s.p.a.ce, but many of them have more to do with philanthropy and domestic economy than with physics. We have seen that, when guest of Lord George Germaine, he was engaged in experiments on gunpowder.

The experiments were made in the usual manner by firing bullets into a ballistic pendulum, and recording the swing of the pendulum. Thompson suggested a modification of the ballistic pendulum, attaching the gun-barrel to the pendulum, and observing the recoil, and making allowance for the recoil due to the discharge from the gun of the products of combustion of the powder, the excess enabled the velocity of the bullet to be calculated. Afterwards he made experiments on the maximum pressure produced by the explosion of powder, and pointed out that the value of powder in ordnance does not depend simply on the whole amount of gas produced, but also on the rapidity of combustion.

While superintending the a.r.s.enal at Munich, Rumford exploded small charges of powder in a specially constructed receiver, which was closed by a plug of well-greased leather, and on this was placed a hemisphere of steel pressed down by a 24-pounder bra.s.s cannon weighing 8081 pounds. He found that the weight of the gun was lifted by the explosion of quant.i.ties of powder varying from twelve to fifteen grains, and hence concluded that, if the products of combustion of the powder were confined to the s.p.a.ce actually occupied by the solid powder, the initial pressure would exceed twenty thousand atmospheres.

Rumford's calculation of the pressure, based upon the bursting of a barrel, which he had previously constructed, is not satisfactory, inasmuch as he takes no account of the fact that the inner portions of the metal would give way long before the outer layers exerted anything like their maximum tension. When a hollow vessel with thick walls, such as a gun-barrel or sh.e.l.l, is burst by gaseous pressure from within, the inner layers of material are stretched to their breaking tension before they receive much support from the outer layers; a rift is thus made in the interior, into which the gas enters, and the surface on which the gas presses being thus increased, the rift deepens till the fracture is complete. In order to gain the full strength due to the material employed, every portion of that material should be stretched simultaneously to the extent of its maximum safe load. This principle was first practically adopted by Sir W. G.

Armstrong, who, by building up the breech of the gun with cylinders shrunk on, and so arranged that the tension increased towards the exterior, availed himself of nearly the whole strength of the metal employed to resist the explosion. Had Rumford's barrel been constructed on this principle, he would have obtained a much more satisfactory result.

These investigations were followed by a very interesting series of experiments on the conducting power of fluids for heat, and, although he pushed his conclusions further than his experiments warranted, he showed conclusively that convection currents are the princ.i.p.al means by which heat is transferred through the substance of fluids, and described how, when a vessel of water is heated, there is generally an ascending current in the centre, and a descending current all round the periphery. Hence it is only when a liquid expands by increase of temperature that a large ma.s.s can be readily heated from below. Water below 39 Fahr. contracts when heated. Rumford, in his paper, enlarges on the bearing of this fact on the economy of the universe, and the following extracts afford a good specimen of his style, and justify some of the statements made by Cuvier in his eulogy:--

I feel the danger to which a mortal exposes himself who has the temerity to undertake to explain the designs of Infinite Wisdom.

The enterprise is adventurous, but it cannot surely be improper.

The wonderful simplicity of the means employed by the Creator of the world to produce the changes of the seasons, with all the innumerable advantages to the inhabitants of the earth which flow from them, cannot fail to make a very deep and lasting impression on every human being whose mind is not degraded and quite callous to every ingenuous and n.o.ble sentiment; but the further we pursue our inquiries respecting the const.i.tution of the universe, and the more attentively we examine the effects produced by the various modifications of the active powers which we perceive, the more we shall be disposed to admire, adore, and love that great First Cause which brought all things into existence.

Though winter and summer, spring and autumn, and all the variety of the seasons are produced in a manner at the same time the most simple and the most stupendous (by the inclination of the axis of the earth to the plane of the ecliptic), yet this mechanical contrivance alone would not have been sufficient (as I shall endeavour to show) to produce that gradual change of temperature in the various climates which we find to exist, and which doubtless is indispensably necessary to the preservation of animal and vegetable life....

But in very cold countries the ground is frozen and covered with snow, and all the lakes and rivers are frozen over in the very beginning of winter. The cold then first begins to be extreme, and there appears to be no source of heat left which is sufficient to moderate it in any sensible degree.

Let us see what must have happened if things had been left to what might be called their natural course--if the condensation of water, on being deprived of its heat, had followed the law which we find obtains in other fluids, and even in water itself in some cases, namely, when it is mixed with certain bodies.

Had not Providence interfered on this occasion in a manner which may well be considered _miraculous_, all the fresh water within the polar circle must inevitably have been frozen to a very great depth in one winter, and every plant and tree destroyed; and it is more than probable that the region of eternal frost would have spread on every side from the poles, and, advancing towards the equator, would have extended its dreary and solitary reign over a great part of what are now the most fertile and most inhabited climates of the world!...

Let us with becoming diffidence and awe endeavour to see what the means are which have been employed by an almighty and benevolent G.o.d to protect His fair creation.

He then goes on to explain how large bodies of water are prevented from freezing at great depths on account of the expansion which takes place on cooling below 39 Fahr., and the further expansion which occurs on freezing, and mentions that in the Lake of Geneva, at a depth of a thousand feet, M. Pictet found the temperature to be 40 Fahr.

"We cannot sufficiently admire the simplicity of the contrivance by which all this heat is saved. It well deserves to be compared with that by which the seasons are produced; and I must think that every candid inquirer who will begin by divesting himself of all unreasonable prejudice will agree with me in attributing them both TO THE SAME AUTHOR....

"But I must take care not to tire my reader by pursuing these speculations too far. If I have persisted in them, if I have dwelt on them with peculiar satisfaction and complacency, it is because I think them uncommonly interesting, and also because I conceived that they might be of value in this age of _refinement_ and _scepticism_.

"If, among barbarous nations, the _fear of a G.o.d_, and the practice of religious duties, tend to soften savage dispositions, and to prepare the mind for all those sweet enjoyments which result from peace, order, industry, and friendly intercourse; a _belief in the existence of a Supreme Intelligence_, who rules and governs the universe with wisdom and goodness, is not less essential to the happiness of those who, by cultivating their mental powers, HAVE LEARNED TO KNOW HOW LITTLE CAN BE KNOWN."

Rumford, in connection with his experiments on the conducting power of liquids, tried the effect of increasing the viscosity of water by the addition of starch, and of impeding its movements by the introduction of eider-down, on the rate of diffusion of heat through it. Hence he explained the inequalities of temperature which may obtain in a ma.s.s of thick soup--inequalities which had once caused him to burn his mouth--and, applying the same principles to air, he at once turned his conclusions to practical account in the matter of warm clothing.

After an attempt to determine, if possible, the weight of a definite quant.i.ty of heat--an attempt in which very great precautions were taken to exclude disturbing causes, while the balance employed was capable of indicating one-millionth part of the weight of the body weighed--Rumford, finding no sensible effect on the balance, concluded that "if the weight of gold is neither augmented nor lessened by _one-millionth part_, upon being heated from the point of _freezing water_ to that of a _bright red heat_, I think we may very safely conclude that ALL ATTEMPTS TO DISCOVER ANY EFFECT OF HEAT UPON THE APPARENT WEIGHTS OF BODIES WILL BE FRUITLESS." The theoretical investigations of Princ.i.p.al Hicks, based on the vortex theory of matter and the dynamical theory of heat, have recently led him to the conclusion that the attraction of gravitation may depend to some extent on temperature.

A series of very valuable experiments on the radiating powers of different surfaces showed how that power varied with the nature of the surface, and the effect of a coating of lamp-black in increasing the radiating power of a body. In order to determine the effect of radiation in the cooling of bodies, Rumford employed the thermoscope referred to by Cuvier. The following pa.s.sage is worthy of attention, as the truth it expounds in the last thirteen words appears to have been but very imperfectly recognized many years after it was written:--

"All the heat which a hot body loses when it is exposed in the air to cool is not given off to the air which comes into contact with it, but ... a large proportion of it escapes in rays, which do not heat the transparent air through which they pa.s.s, but, like light, generate heat only when and where they are stopped and absorbed."

Rumford then investigated the absorption of heat by different surfaces, and established the law that good radiators are good absorbers; and recommended that vessels in which water is to be heated should be blackened on the outside. In speculating on the use of the colouring matter in the skin of the negro, he shows his fondness for experiment:--

"All I will venture to say on the subject is that, were I called to inhabit a very hot country, nothing should prevent me from making the experiment of blackening my skin, or at least, of wearing a black s.h.i.+rt, in the shade, and especially at night, in order to find out if, by those means, I could contrive to make myself more comfortable."

In his experiments on the conduction of heat, Rumford employed a cylinder with one end immersed in boiling water and the other in melting ice, and determined the temperature at different points in the length of the cylinder. He found the difficulty which has recently been forcibly pointed out by Sir Wm. Thomson, in the article "Heat,"

in the "Encyclopaedia Britannica," viz. that the circulation of the water was not sufficiently rapid to keep the temperature of the layer in contact with the metal the same as that of the rest of the water; and he also called attention to the arbitrary character of thermometer-scales, and recommended that more attention should be given to the scale of the air thermometer. It was in his visit to Edinburgh, in 1800, that, in company with some of the university professors, the count conducted some experiments in the university laboratory on the apparent radiation of cold. Rumford's views respecting _frigorific rays_ have not been generally accepted, and Prevost's theory of exchanges completely explains the apparent radiation of cold without supposing that cold is anything else than the mere absence of heat.

We must pa.s.s over Rumford's papers on the use of steam as a vehicle of heat, on new boilers and stoves for the purpose of economizing fuel, and all the papers bearing on the nutritive value of different foods.

The calorimeter with which he determined the amount of heat generated by the combustion, and the latent heat of evaporation, of various bodies has been already alluded to. Of the four volumes of Rumford's works published by the American Academy of Arts and Sciences, the third is taken up entirely with descriptions of fireplaces and of cooking utensils.

Before deciding on the best way to light the military workhouse at Munich, Rumford made a series of experiments on the relative economy of different methods, and for this purpose designed his well-known shadow-photometer. In the final form of this instrument the shadows were thrown on a plate of ground gla.s.s covered with paper, forming the back of a small box, from which all extraneous light was excluded. Two rods were placed in front of this screen, and the lights to be compared were so situated that the shadow of one rod thrown by the first light might be just in contact with that of the other rod thrown by the second light. By introducing coloured gla.s.ses in front of the lights, Rumford compared the illuminating powers of different sources with respect to light of a particular colour. The complementary tints exhibited by the shadows caused him to devise his theory of the harmony of complementary colours. One result is worthy of mention: it is a conclusion to which public attention has since been called in connection with "duplex" burners. Rumford found that with wax tapers the amount of light emitted per grain of wax consumed diminished with the diminution of the consumption, so that a small taper gave out only one-sixteenth as much light as an ordinary candle for the same consumption of wax. He says:--