believing in the doctrine, which he had practiced throughout his life, that selfeducation is the only true one."

And it is of interest to remark that Joule, who after Dalton trod the path of eminence in discovery, was a pupil of Dalton, taking for three or four years Frivate lessons in physics, and beyond tnis was entirely self-educated in science, becoming very early an enthusiast in original research, and the maker at 19 of an electro-magnetic engine.

Dalton was born, the son of a handloom weaver, September 6, 1766. His parents were Quakers, and he was throughout life a singularly fine type of the Quaker man; sometimes, not to say often, a plain, almost brusque man; at other times a singularly interesting gentleman. The boy Dalton, although he did so much for himself, was yet particularly helped in starting by an excellent Quaker schoolmaster to whom he was sent, and also by a Quaker gentleman of some scientific and literary distinction, who not only assisted young Dalton in. his studies, but gave him special instruction. The early schooling which he had, until 11 years of age, carried him through a course of mensuration, surveying, navigation, etc.

Teacher and Stu

dent of Nature

The school of which the

Quaker youth was principal at twelve years of age, was carried on in an old barn at first, then in his father's cottage, and later in the Quaker meeting-house. The emoluments were not over about $1.25 a week; worth, perhaps, at that time, as much again as at present. After two years of this, the youth tried work with a farmer, and followed the plow as possibly more remunerative than playing pedagogue on a small scale.

At 15 years of age Dalton walked forty-four miles from his country home to Kendal, a considerable town, where his brother and a friend were carrying on a school. His school-keeping at Kendal continued for twelve years, until 1793, when he found a place as teacher at Manchester for six years, after which he was a private teacher, devoting a great part of his time to researches in science.

As early as 1787 Dalton began with public lectures, to which from that time, for some years, he devoted considerable attention. He never became a popular

expositor of science from the platform of the lecturer, and with the rough exterior and uncouth demeanor of his earlier years, not to speak of his Cumberland dialect, which said "Yan med deu't" for "You may do it," his public efforts could not have added much either to his income or to his courage in pursuing thankless tasks. Happily, the indomitable energy of his character made him independent of aids of circumstance.

In these earlier years he made botanical collections, when as yet scientific botany was non-existent, and went from plants to insects without help from entomology. Some of these, he wrote,

may be thought puerile; but nothing. that enjoys animal life, or that vegetates, is beneath the dignity of a naturalist to examine." He experimented on the vitality of snails, mites and maggots, and upon his own vital energy in its connection with food, seeking to penetrate "the cause of disease and of health," and for a time seriously thinking of taking medicine as his profession.

On coming to Manchester, in 1793, Dalton became tutor in mathematics and natural philosophy and chemistry in an institution of high and liberal aims, which stood as an academy at Manchester until 1803; then found a seat at York until 1840, again rested a short time at Manchester, as "Manchester New College;" and after transference to London, where, from 1853, the celebrated Dr. James Martineau was its chief light, was in 1889 made the chief English liberal divinity school as

Oxford.

"Manchester College," at

way a manufacturer of these instruments. A volume of his meteorological observations was published in 1793. From about 1792, when he had an opportunity, on October 13th, to observe a grand auroral display, Dalton made a special study of the connection between auroral displays and the earth's magnetism. Living, as he did, for twenty-six years, in the beautiful lake district of the northwest of England, not only the hills and the lakes, the fells and the streams, became familiar to him, but the changing skies, the varying climate, and the heavens at night, were the pages of a great book of nature in which he took unwearied delight, and from which he drew lessons of knowledge such as books could not give him. It was, indeed, characteristic of his self-educated originality, that he preferred to be independent of what books could tell him, and to speak as much as possible from his own observations and experience. In the matter of the auroral light, which, says Sir Henry Roscoe, has been made to tell us its story, yet without permitting us to read the riddle of a bright green line always found in its spectrum, Dalton guessed correctly its connection with the earth's magnetism; but to this sound judgment he added the assumption, which our knowledge now fails to support, that there must be something of the nature of iron or magnetic steel in the auroral beam.

The Causes

of Winds

The attention which Dalton gave to atmospheric disturbances, without knowing that the history of the subject already formed a chapter of sound science, led him to the wholly true, complete, and accurate conclusion, that "the inequality of heat in the different climates and places, and the earth's rotation on its axis, are the grand and chief causes of winds, both regular and irregular, in comparison with which all the rest are trifling and insignificant."

In this connection Sir Henry Roscoe remarks that Dalton's essays on the barometer, on the thermometer and their variations, on the aurora, on rainfall, on the formation of clouds, on evaporation, and on the distribution and character of atmospheric moisture, written, as they were, at the end of the last century, might well be considered as remarkable productions from the pen of an experienced philosopher; although they were, in fact, written by a young schoolmaster,

ignorant, to a great extent, of what had been written by others, and out of reach of libraries and books of reference.

Dalton's study of evaporation led to a law of vapors, which is called his, and according to which it is understood that aqueous vapor always exists independently in the air, not held by or attached to the oxygen or nitrogen of the air, and that the same weight of the vapor is taken up by a given space, at a given degree of heat, whether that space be or be not filled with air.

The Theory

of Rain

Dalton was the first, not indeed to suggest, but to render certain, that rain is caused, not by any alteration in atmospheric pressure but simply and solely by a diminution of temperature. He made clear that when moist air is cooled below what we know as the dew-point, the aqueous vapor in a very fine form condenses into larger particles, forming clouds, and upon further condensation giving drops, which fall as rain; an enormous weight of water thus falling: from a cubic mile of air, for instance, which is a minute fraction of the whole over any locality, no less than 140,000 tons of rain or snow falling, if the air, at 95° of summer heat, has taken up all that it can, and precipitation is brought about by the temperature falling to the freezing point.

Remarkable

Prediction

Long before Faraday had published his first experiments, in 1821, on the condensation of the so-called permanent gases, Dalton predicted, not only what Faraday accomplished, but what we now know, that all gases, including probably even hydrogen, which is found to be by far the most refractory, can be liquefied, and even solidified. "There can scarcely be a doubt entertained," he said, "respecting the reducibility of all elastic fluids [i. e. gases] of whatever kind into liquids; and we ought not to despair of effecting it in low temperatures, and by strong pressure exerted upon the unmixed gases.

A paper which Dalton brought to notice June 27, 1800, dealt with "the heat and cold produced by the mechanical condensation and rarefaction of air," in a way to suggest that equivalency of mechanical energy and heat which was afterwards fully studied out by Manchester's other eminent discoverer in science,

Joule, the founder of modern physics. Dalton made the first attempt to measure the amount of heat evolved by compression and that absorbed in rarefaction, and it was when, forty years after, his determinations were repeated, that an advance began to which Joule gave monumental completion.

At this date, 1800, Dalton became secretary to the Manchester Philosophical Society. He became a vice-president in 1808, and from 1817 to his death, in 1844, he filled the office of president, and gave to the world, through it, the long series of his masterly researches.

Color-Vision

A most remarkable and Experiences interesting chapter in the story of Dalton's life is that of his expericnce of wrong color-vision, seeing certain colors wrongly, and the researches by which he made the subject of such wrong color-vision known to the scientific world. He had lived to the age of 26 before he became aware that he saw certain colors wrongly; scarlet, for instance, being seen by him as drab. The story goes that when he made his Quaker mother a present of a pair of stockings marked in a shopwindow "silk, and newest fashion," she found them to be a bright scarlet, while to his sight they were a dark-bluish drab. He and his brother Jonathan both saw them as drab, and insisted that their mother's eyes must see wrong. Her neighbors, however, sustained her declaration that the stockings were "varra fine stuff, but uncommon scarlety." It further proved that Dalton saw green as a reddish snuff color. At a tailor's he proposed to have a coat of Quaker drab made from a piece of such scarlet cloth as was in use for hunting-coats. Pink he saw as skyblue. Pinks and roses he saw as lightblue by day and a reddish-yellow by night; crimson as a bluish-dark drab, and grass-green as a red or blood color. The rosy blush of a cheek was to him a lightblue. While persons ordinarily see red, orange, yellow, green, blue, and purple, his sight he described as follows:

"My yellow comprehends the red, orange, yellow, and green of others; and my blue and purple coincides with theirs. That part of the image [of the sun, the colors of the spectrum] which others call red, appears to me little more than a shade, or defect of light; after that, the orange, yellow, and green, seem one

color, which descends pretty uniformly from an intense to a rare yellow, making what I call different shades of yellow. The difference between the green part and the blue part is very striking to my eye; they seem to be strongly contrasted. That between the blue and purple is much less so. The purple appears to be much darkened and condensed.

"Under Red (by daylight) I include crimson, scarlet, red, and pink. All crimsons appear to me to consist chiefly of dark-blue; but many of them seem to have a strong tinge of dark-brown. I have seen specimens of crimson, claret, and mud which were very near alike. Crimson has a grave appearance, being the reverse of every showy and splendid color. Woolen yarn, dyed crimson or dark-blue, is the same to me. Pink seems to be composed of nine parts of light-blue and one of red, or some color which has no other effect than to make the lightblue appear dull and faded a little.

"The color of a florid complexion appears to me that of a dull, opaque, blackish-blue upon a white ground. Dilute black ink upon white paper gives a color resembling that of a florid complexion. It has no resemblance of the color of blood. Blood appears to me not unlike that color called bottle-green.

"By candle-light red and scarlet appear much more vivid than by day. Crimson loses its blue and becomes yellowish-red. Pink is by far the most changed-indeed, it forms an excellent contrast to what it is by day. No blue now appears; yellow has taken its place. Pink, by candle-light, seems to be three parts yellow and one red, or a reddishyellow. The blue, however, is less mixed by day than the yellow by night. Red, and particularly scarlet, is a superb color by candle-light; but by day some reds are the least showy imaginable. I should call them dark drabs.

"I do not find that I differ materially from other persons in regard to orange and yellow, by daylight and by candlelight.

Green, by daylight, I take my idea of from grass. This appears to me red; the face of a laurel leaf a good match to a stick of red sealing-wax, and the back of the leaf the lighter red of wafers. Green woolen cloth appears to me a dull, dark, brownish-red color. A mixture of two parts mud and one red would come near to it.

Self-Education

The eminence of Dalin Chemistry ton as a discoverer in chemistry was achieved without any aid from education in that science. Up to 1796, when he was 30 years old, there is no evidence that he had taken any special interest in chemical research. But when his interest had been excited by hearing a course of lectures on chemistry, he at once undertook experiments, and occupied his mind with reflections looking to finding out the laws of chemical change.

He saw clearly that study of the chemical and physical properties of gases especially, promised revelation of the secrets of nature which he desired to penetrate. He succeeded, according to his own view, not so much from having any exceptional genius as from unwearied assiduity in research. Yet his unwearied attention to study, and his untiring perseverance, were not without a high degree of genius or intellectual insight.

Discovery of As early as October of Important Laws 1801, Dalton gave a series of papers on the constitution of mixed gases, in which were brought to view four important laws which form the basis of our present knowledge. By these laws were brought out the facts:

1. That when two gases are mixed together, as oxygen and nitrogen, in the air, their particles do not mutually repel each other, or press upon each other, but those of each gas move and are pressed precisely as if those of the other were not present.

2. The force of steam from all liquids is the same at equal distances above or below the several temperatures at which they boil in the open air, and is the same under any pressure of another gas as it would be in a vacuum.

3. The quantity of any liquid evaporated in the open air is directly as the force of steam from such liquid at its temperature, all other circumstances being the

same.

4. All gases expand the same quantity by heat, and very nearly in the same equable way as mercury.

The expansion of gases and vapors by heat was discussed and its law established by Dalton, who found that for equal increments of temperature all gases expand equally. This law is properly called Dalton's, because he first announced it and gave experimental evidence of its truth.

In the essay on this law Dalton gave a diagram to illustrate his conception of the constitution of the air, which indicates that his mind had begun to distinctly picture atoms as composing gases.

Further experimental inquiry brought out the fact that the oxygen and nitrogen of the air exist in a constant definite proportion which may be roughly stated at that of oxygen one part, and nitrogen four parts, the two gases being diffused precisely as either would be in a vacuum.

Discovery

Germ of Great The first germ of his great discovery of the law of chemical combination in multiple proportions appears in his making out the fact that when oxygen and nitrous gas are united it appears that the oxygen may unite with one definite portion of nitrous gas, to form nitric acid, and with twice that portion, neither less nor more, to form nitrous acid Here was the first inkling got by Dalton of his great law, according to which chemical combination proceeds, not by proceeds, not by indefinite varying amounts uniting, but by a definite invariable portion, or number of portions-one, two, or three full portions, and never some part of a portion.

The investigation by Dalton of the way in which a gas is dissolved in and diffused through water, contributed some light in the direction of the theory of atoms which he was rapidly working out. He conceived the gas as a mass of particles which move about in the water, mutually repelling one another, precisely as in a vacuum. Some altogether erroneous ideas were brought by Dalton into his theory of the solubilty of gases in water, but out of it all came the grand discovery embodied in a "Table of Relative Weights of