Part 10 (1/2)

”This result can be easily explained if we admit the hypothesis which supposes light to be a.n.a.logous to sound.... The particles ... were so rapidly cooled ... that they had hardly time to s.h.i.+ne one instant before they became too cold to be any longer visible.”

An argand lamp, when compared with a lamp having a flat wick, gave more light in the ratio of 100 to 85 for the same consumption of oil.

One of the latest investigations of Rumford was that bearing on the effect of the width of the wheels on the draught of a carriage. To his own carriage, weighing, with its pa.s.sengers, nearly a ton, he fitted a spring dynamometer by means of a set of pulleys attached to the under-carriage and the splinter-bar. He used three sets of wheels, respectively 1-3/4, 2-1/4, and 4 inches wide, and, introducing weights into the carriage to make up for the difference in the weights of the wheels, he found a very sensible diminution in the tractive force required as the width of the wheels was increased, and in a truly scientific spirit, despising the ridicule cast upon him, he persisted in riding about Paris in a carriage with four-inch tyres.

But the piece of work by which Rumford will be best known to future generations is that described in his paper ent.i.tled ”An Inquiry concerning the Source of the Heat which is excited by Friction.” It was while superintending the boring of cannon in the a.r.s.enal at Munich that Rumford was struck with the enormous amount of heat generated by the friction of the boring-bar against the metal. In order to determine whether the heat had come from the chips of metal themselves, he took a quant.i.ty of the abraded borings and an equal weight of chips cut from the metal with a fine saw, and, heating them to the temperature of boiling water, he immersed them in equal quant.i.ties of water at 59-1/2 Fahr. The change of temperature of the water was the same in both cases, and Rumford found that there was no change which he could discover _in regard to its capacity for heat_ produced in the metal by the action of the borer.

In order to prevent the honeycombing of the castings by the escaping gas, the cannon were cast in a vertical position with the breech at the bottom of the mould and a short cylinder projecting about two feet beyond the muzzle of the gun, so that any imperfections in the casting would appear in this projecting cylinder. It was on one of these pieces of waste metal, while still attached to the gun, that Rumford conducted his experiments. Having turned the cylinder, he cut away the metal in front of the muzzle until the projecting piece was connected with the gun by a narrow cylindrical neck, 22 inches in diameter and 38 inches long. The external diameter of the cylinder was 775 inches, and its length 98 inches, and it was bored to a depth of 72 inches, the diameter of the bore being 37 inches. The cannon was mounted in the boring-lathe, and a blunt borer pressed by a screw against the bottom of the bore with a force equal to the weight of 10,000 pounds. A small transverse hole was made in the cylinder near its base for the introduction of a thermometer. The cylinder weighed 11313 pounds, and, with the gun, was turned at the rate of thirty-two revolutions per minute by horse-power. To prevent loss of heat, the cylinder was covered with flannel. After thirty minutes' work, the thermometer, when introduced into the cylinder, showed a temperature of 130 Fahr. The loss of heat during the experiment was estimated from observations of the rate of cooling of the cylinder. The weight of metal abraded was 837 grains, while the amount of heat produced was sufficient to raise nearly five pounds of ice-cold water to the boiling point.

To exclude the action of the air, the cylinder was closed by an air-tight piston, but no change was produced in the result. As the air had access to the metal where it was rubbed by the piston, and Rumford thought this might possibly affect the result, a deal box was constructed, with slits at each end closed by sliding shutters, and so arranged that it could be placed with the boring bar pa.s.sing through one slit and the narrow neck connecting the cylinder with the gun through the other slit, the sliding shutters, with the help of collars of oiled leather, serving to make the box water-tight. The box was then filled with water and the lid placed on. After turning for an hour the temperature was raised from 60 to 107 Fahr., after an hour and a half it was 142 Fahr., at the end of two hours the temperature was 178 Fahr., at two hours and twenty minutes it was 200 Fahr., and at two hours and thirty minutes it ACTUALLY BOILED!

”It would be difficult to describe the surprise and astonishment expressed in the countenances of the bystanders on seeing so large a quant.i.ty of cold water heated and actually made to boil without any fire.

”Though there was, in fact, nothing that could justly be considered as surprising in this event, yet I acknowledge fairly that it afforded me a degree of childish pleasure which, were I ambitious of the reputation of a _grave philosopher_, I ought most certainly rather to hide than to discover.”

Rumford estimated the ”total quant.i.ty of ice-cold water which, with the heat actually generated by the friction and acc.u.mulated in two hours and thirty minutes, might have been heated 180 degrees, or made to boil” at 2658 pounds, and the rate of production he considered exceeded that of nine wax candles, each consuming ninety-eight grains of wax per hour, while the work of turning the lathe could easily have been performed by one horse. This was the first rough attempt ever made, so far as we know, to determine the mechanical equivalent of heat.

In his reflections on these experiments, Rumford writes:--

It is hardly necessary to add that anything which any _insulated_ body or system of bodies can continue to furnish _without limitation_ cannot possibly be _a material substance_; and it appears to me to be extremely difficult, if not quite impossible, to form any distinct idea of anything capable of being excited and communicated in the manner the heat was excited and communicated in these experiments, except it be MOTION.

It has been stated that, if Rumford had dissolved in acid the borings and the sawn strips of metal, the capacity for heat of which he determined, and had shown that the heat developed in the solution was the same in the two cases, his chain of argument would have been absolutely complete. Considering the amount of heat produced in the experiments, there are few minds whose conviction would be strengthened by this experiment, and it is only those who look for faultless logic that will refuse to Rumford the credit of having established the dynamical nature of heat.

Davy afterwards showed that two pieces of ice could be melted by being rubbed against one another in a vacuum, but he does not appear to have made as much as he might of the experiment. Mayer calculated the mechanical equivalent of heat from the heat developed in the compression of air, but he _a.s.sumed_, what afterwards was shown by Joule to be nearly true, that the whole of the work done in the compression was converted into heat. It was Joule, however, who first showed that heat and mechanical energy are mutually convertible, so that each may be expressed in terms of the other, a _given_ quant.i.ty of heat always corresponding to the _same amount_ of mechanical energy, whatever may be the intermediate stages through which it pa.s.ses, and that we may therefore define the mechanical equivalent of heat as _the number of units of energy which, when entirely converted into heat, will raise unit ma.s.s of water one degree from the freezing point_.

THOMAS YOUNG.

”We here meet with a man altogether beyond the common standard, one in whom natural endowment and sedulous cultivation rivalled each other in the production of a true philosopher; nor do we hesitate to state our belief that, since Newton, Thomas Young stands unrivalled in the annals of British science.” Such was the verdict of Princ.i.p.al Forbes on one who may not only be regarded as one of the founders of the undulatory theory of light, but who was among the first to apply the theory of elasticity to the strength of structures, while it is to him that we are indebted in the first instance for all we know of Egyptian hieroglyphics, and for the vast field of antiquarian research which the interpretation of these symbols has opened up.

Thomas Young was the son of Thomas and Sarah Young, and the eldest of ten children. His mother was a niece of the well-known physician, Dr.

Richard Brocklesby, and both his father and mother were members of the Society of Friends, in whose principles all their children were very carefully trained. It was to the independence of character thus developed that Dr. Young attributed very much of the success which he afterwards attained. He was born at Milverton, in Somersets.h.i.+re, on June 13, 1773. For the greater part of the first seven years of his life he lived with his maternal grandfather, Mr. Robert Davis, at Minehead, in Somersets.h.i.+re. According to his own account, he could read with considerable fluency at the age of _two_, and, under the instructions of his aunt and a village schoolmistress, he had ”read the Bible twice through, and also Watts's Hymns,” before he attained the age of four. It may with reason be thought that both the schoolmistress and the aunt should have been severely reprimanded, and it is certain that their example is not to be commended; but Young's infantile const.i.tution seems to have been proof against over-pressure, and before he was five years old he could recite the whole of Goldsmith's ”Deserted Village,” with scarcely a mistake. He commenced learning Latin before he was six, under the guidance of a Nonconformist minister, who also taught him to write. When not quite seven years of age he went to boarding-school, where he remained a year and a half; but he appears to have learned more by independent effort than under the guidance of his master, for privately he ”had mastered the last rules of Walkinghame's 'Tutor's a.s.sistant'” before reaching the middle of the book under the master's inspection. After leaving this school, he lived at home for six months, but frequently visited a neighbour who was a land surveyor, and at whose house he amused himself with philosophical instruments and scientific books, especially a ”Dictionary of Arts and Sciences.” When nearly nine he went to the school of Mr. Thompson, at Compton, in Dorsets.h.i.+re, where he remained nearly four years, and read several Greek and Latin authors, as well as the elements of natural philosophy--the latter in books lent him by Mr. Jeffrey, the a.s.sistant-master. This Mr. Jeffrey appears to have been something of a mechanical genius, and he gave Young lessons in turning, drawing, bookbinding, and the grinding and preparation of colours. Before leaving this school, at the age of thirteen, Young had read six chapters of the Hebrew Bible.

During the school holidays the construction of a microscope occupied considerable time, and the reading of ”Priestley on Air” turned Young's attention to the subject of chemistry. Having learned a little French, he succeeded, with the help of a schoolfellow, in gaining an elementary knowledge of Italian. After leaving school, he lived at home for some time, and devoted his energies mainly to Hebrew and to turning and telescope-making; but Eastern languages received a share of attention, and by the time he was fourteen he had read most of Sir William Jones's ”Persian Grammar.” He then went to Youngsbury, in Hertfords.h.i.+re, and resided at the house of Mr. David Barclay, partly as companion and partly as cla.s.sical tutor to Mr. Barclay's grandson, Hudson Gurney. This was the beginning of a friends.h.i.+p which lasted for life. Gurney was about a year and a half junior to Young, and for five years the boys studied together, reading the cla.s.sical works which Young had previously studied at school. Before the end of these five years Young had gained more or less acquaintance with fourteen languages; but his studies were for a time delayed through a serious illness when he was little more than sixteen. To this illness his uncle, Dr. Brocklesby, referred in a letter, of which the following extract is interesting for several reasons:--

Recollect that the least slip (as who can be secure against error?) would in you, who seem in all things to set yourself above ordinary humanity, seem more monstrous or reprehensible than it might be in the generality of mankind. Your prudery about abstaining from the use of sugar on account of the negro trade, in any one else would be altogether ridiculous, but as long as the whole of your mind keeps free from spiritual pride or too much presumption in your facility of acquiring language, which is no more than the dross of knowledge, you may be indulged in such whims, till your mind becomes enlightened with more reason. My late excellent friend, Mr. Day, the author of 'Sandford and Merton,' abhorred the base traffic in negroes'

lives as much as you can do, and even Mr. Granville Sharp, one of the earliest writers on the subject, has not done half as much service in the business as Mr. Day in the above work. And yet Mr. Day devoured daily as much sugar as I do; for he reasonably concluded that so great a system as the sugar-culture in the West Indies, where sixty millions of British property are employed, could never be affected either way by one or one hundred in the nation debarring themselves the reasonable use of it. Reformation must take its rise elsewhere, if ever there is a general ma.s.s of public virtue sufficient to resist such private interests. Read Locke with care, for he opens the avenues of knowledge, though he gives too little himself.

With respect to the sugar, no doubt very much may be said on Young's side of the question. It appears, however, that in his early manhood there was a good deal in his conduct which to-day would be regarded as _priggish_, though it was somewhat more in harmony with the spirit of his time.

He left Youngsbury at the age of nineteen, having read, besides his cla.s.sical authors, the whole of Newton's ”Principia” and ”Opticks,”

and the systems of chemistry by Lavoisier and Nicholson, besides works on botany, medicine, mineralogy, and other scientific subjects. One of Young's peculiarities was the extraordinary neatness of his handwriting, and a translation in Greek iambics of Wolsey's farewell to Cromwell, which he sent, written very neatly on vellum, to his uncle, Dr. Brocklesby, attracted the attention of Mr. Burke, Dr.

Charles Burney, and other cla.s.sical scholars, so that when, a few months later, Young went to stay with his uncle in London, and was thrown into contact with some of the chief literary men of the day, he found that his fame as a scholar had preceded him. This neatness of his handwriting and his power of drawing were of great use in his researches on the Egyptian hieroglyphics. He had little faith in natural genius, but believed that anything could be accomplished by persevering application.

”Thou say'st not only skill is gained, But genius too may be obtained, By studious imitation.”

In the autumn of 1792 Young went to London for the purpose of studying medicine. He lived in lodgings in Westminster, and attended the Hunterian School of Anatomy. A year afterwards he entered St.

Bartholomew's Hospital as a medical student. The notes which he took of the lectures were written sometimes in Latin, interspersed with Greek quotations, and not unfrequently with mathematical calculations, which may be a.s.sumed to have been made before the lecture commenced.

During his school days he had paid some attention to geometrical optics, and had constructed a microscope and telescope. Now his attention was attracted to a far more delicate instrument--the eye itself. Young had learned how a telescope can be ”focussed” so as to give clear images of objects more or less distant. Some such power of adjustment must be possessed by the eye, or it could never form distinct images of objects, whether at a distance of a foot or a mile. The apparently fibrous structure of the crystalline lens of the eye had been noticed and described by Leuwenhoeck; and Pemberton, a century before Young took up the subject, had suggested that the fibres were muscles, by the action of which the eye was ”accommodated”

for near or distant vision. In dissecting the eye of an ox Young thought he had discovered evidence confirmatory of this view, and the paper which he wrote on the subject was not only published in the ”Philosophical Transactions,” but secured his election as a Fellow of the Royal Society in June, 1794. This paper was important, not simply because it led to Young's election to the Royal Society, but mainly because it was his first published paper on optical subjects. Later on he showed incontestably, by exact measurements, that it is the crystalline lens which changes its form during adjustment; but he was wrong in supposing the fibres of the lens to be muscular. By carefully measuring the distance between the images of two candles formed by reflection from the cornea, he showed that the cornea experienced no change of form. His eyes were very prominent; and turning them so as to look very obliquely, he measured the length of the eye from back to front with a pair of compa.s.ses whose points were protected, pressing one point against the cornea, and the other between the back of the eye and the orbit, and showed that, when the eye was focussed for different distances, there was no change in the length of the axis.