so difficult was it considered 'in those days to procure a regular circular movement directly from these engines, that it was proposed by engineers of ability to apply their power to raise water in the usual way, and then cause that water to fall upon a water-wheel, by which the circular motion would be obtained. But the genius of Watt soon devised means of applying the new power to produce the circular movement. He made the steam press the piston up as well as down by ingenious arrangements of the valves; and by a number of the most beautiful contrivances, which seemed to rush into his mind just as they were required, he adapted the boiler and engine to yield from the alternate rectilineal movement of the piston a steady, uniform, circular motion. For this, called the double-acting engine, Watt took out a patent in 1782, and since that time this engine has been the chief moving-power employed for impelling machinery, and it has not been necessary to confine manufactories to those localities where waterpower could be had, nor have they been dependent on the weather for supplies of water, or of the still more precarious element-wind. Useful labour is not now brought to a stand because the streams are dried up, or the wind ceases to blow; but at all places, times, and seasons, wherever fuel can be had and a little water— for these are the food of the steam-engine-there this great power may be set to labour for the good of mankind. It is now in action in every quarter of the world, doing the world's work, raising water and mineral treasures from the bowels of the earth, carrying from place to place, on land or over the waters, ploughing, reaping, grinding, hammering, turning, boring, printing, and assisting in every factory; serving mankind night and day all the year round, and doing for them what would require the force of millions of horses, and much of which could not be done at all without its powerful aid. No invention, except that of printing, has done so much for the progress of civilization and the useful arts.

13. We cannot have any adequate conception of the wonderful fertility of inventive genius displayed by

Watt, unless we are able to contrast the imperfect form and limited powers of the rude machine upon which he had to work, with the highly-finished state and varied powers of the engine which he produced. Not only did he render it infinitely more powerful and economical in its action, and capable of application to an infinite variety of purposes, but, by a number of contrivances of very great ingenuity, he made it self-regulating, so that, when once set in action, it adjusted its rate of movement to the work to be done, and the consumption of fuel to the rate of movement required. With but little change it was afterwards adapted to the propulsion of ships; and steam navigation is now established between the most distant places on the earth's surface. This very important application was first successfully made in the United States of America in 1807, and in this country in 1812; both of which Watt happily lived to witness.

14. In 1800, when the patent granted him by Parliament expired, Watt retired from business; but he survived till 1819, when he died at his seat, Heathfield, near Birmingham, at the advanced age of eighty-three years. Men then felt that a master-spirit, one of the greatest benefactors of the human race, had passed away. Shortly after his death, public meetings were held in the leading towns of the kingdom, which were attended by the most distinguished men of each district, who united in the warmest eulogiums on the genius and character of Watt, and on the inestimable benefits he had conferred on mankind. Subscriptions were entered into, and monuments erected to his memory in Westminster Abbey, and many other places throughout the country. In 1814, he had had the high honour conferred upon him of being chosen one of the eight foreign associates, of the most illustrious scientific body in the world-the National Institute of France; and some years after his death, an Eloge, comprising a memoir of his life, was read before this body by the distinguished French philosopher, Arago, which has been translated and published in this country.

15. James Watt was not a mere mechanician. He

was a man of great general information, and of a highlycultivated mind. His talents and fancy," says his celebrated countryman Sir Walter Scott, "overflowed on every subject. One gentleman was a deep philologist, he talked with him on the origin of the alphabet, as if he had been coeval with Cadmus ; another a celebrated critic,-you would have said that the old man had studied political economy and belles-lettres all his life;-of science, it is unnecessary to speak, it was his own distinguished walk. And yet when he spoke with your countryman, you would have supposed he had been coeval with Clavers and Burley, with the persecutors and persecuted; and could number every shot that the dragoons had fired at the fugitive Covenanters." From his boyhood upwards, Watt possessed a rich fund of anecdote, and was in the habit of entertaining his friends with tales-improvised romances— which he composed as he went along, containing the usual incidents, adventures, escapes, descriptions of costume, character, and scenery, found in such compositions. This practice, begun in his early youth, he continued to a late period of life.

16. James Watt was twice married, and had two sons, one of whom survived him. The other, Mr. Gregory Watt, had given early promise of scientific eminence, but died while still a youth. The name of Watt, however, will live in the memories of men, so long as they continue to honour the successful application of genius to benefit the human race. While the steam-engine remains the chief means of furnishing moving-power, the man who first rendered it thoroughly efficient must be held in remembrance: and should it ever be displaced by some new source of power, men will not readily forget the great deeds it has done during the present century, nor the name of him whose inventive genius armed it with these extraordinary powers.-HUGO REID.

Geology.

LESSON I.

THE ART OF MINING.

BY WARINGTON SMYTH.

"As for the earth out of it cometh bread: and under it is turned up as it were fire" "The stones of it are the place of sap

phires: and it hath dust of gold."

1. GENERAL CHARACTER OF MINERAL DEPOSITS.-The minerals which it is the object of the miner to search for and extract are, for the most part, met with in one of two kinds of deposits, in beds or in veins; the former accumulated during the formation of the rocks with which they are associated, the latter introduced at some later period.

The beds, strata, seams, or sills, as they are locally termed, are characterized by lying parallel to the stratified sheets of rock, clay, &c., which spread above and below them; and having been subjected with them to the same movements of elevation, depression, contortion, and dislocation, offer greater or less difficulty to the operations of the miner according to the prevalence of these disturbances. The value, therefore, of a deposit of this kind must depend in part on its freedom from such accidents, as well as on its constituent substances and thickness. Sometimes the entire stratum is formed of the workable material, as, for example, certain beds of coal; whilst more frequently a portion only can be extracted to advantage, and the remainder is regarded as refuse, this being commonly the case in the numerous beds of iron ore which form so important an element in the mining industry of Great Britain.

2. If of great intrinsic value, or favoured by local circumstances, beds may be worked, when their thickness is very small, as the copper-bearing slate of Mansfeldt in Prussian Saxony, which is in some places no more than six inches thick; and certain seams of coal worked in the hilly districts of Northern England are so thin, that the excavations opened by the colliers are not more than twenty inches in height.

On the other hand, beds, even when composed chiefly of one kind of mineral, sometimes attain very great dimensions, as do the strata of rock-salt, which are often above thirty feet in thickness, the Dudley seam of coal, amounting occasionally to nearly forty feet, and some beds of lignite, or brown coal, to as much as sixty feet, rendering it necessary to employ peculiar methods of mining to extract them with safety.

3. A particular variety of these stratified deposits is formed by the beds of clay and gravel which have been carried down from higher grounds by the action of streams of water, and contain grains and lumps of tin ore, iron ores, platinum, and gold, broken and washed away from their original position.

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These constitute what are called the stream works in Cornwall, which have been explored for tin from the earliest ages, and the alluvial layers or diggings" which have, of late years, been so productive of gold in Siberia, California, and Australia.

4. Veins or lodes are the principal sources of the ores which produce silver, copper, lead, tin, and the numerous other metals more or less important in the arts and manufactures. Imagine a crack or fissure running through the crust of the earth from the surface downwards to an unknown depth, extending in a nearly straight line for a few hundred yards or for several miles in length, and of a width which varies in different cases from an inch to above one hundred

feet; then suppose this crack to be filled with a mixture of minerals and fragments of the rock which it intersects, and you have the general character of a lode or mineral vein. Of the minerals which compose its substance, some, of the description called spars, contain no useful metal, as quartz, calc-spar, heavyspar, fluor, &c.; and when these preponderate, the lode is said to be poor. The metalliferous minerals are, for the most part, combinations of the metals with oxygen, or with sulphur, or arsenic: more rarely the metals are found in their native state, or forming salts by the union of their oxides with acids. Thus the most important ores of copper in Great Britain are the oxides