which appears to have been the same with that now called stereotype. This invention is singular for its vicissitudes of notoriety and oblivion. The Chinese have had a long acquaintance with the art of printing from blocks or plates, instead of moveable types, and among them it is to this day the only method in use. It was probably also the first form which the art of printing assumed in Europe-was then forgotten for many years, till it was revived in the middle of the sixteenth century at Augsburg, where some of the plates that were used for the purpose are still preserved-was again introduced at Leyden about half a century later-was a few years after reinvented by Canstein-was practised at Edinburgh in 1744 by William Ged, who was quite ignorant of what had been done by his predecessors—and, lastly, after his attempts had ceased to be remembered, was taken up anew by the late ingenious Dr. Alexander Tilloch, and Fowlis, the Glasgow printer, who, however, did little more than merely take out a patent for what they deemed their discovery. These block or plate printers, however, did not all pursue the same method. Faust, for instance, on the invention of printing, employed merely wooden blocks, such as are used by the Chinese, on which the characters were cut out, as is done still in wood-engraving; the Augsburg printers appear to have set up their types in the usual manner, and then to have converted them into a solid plate by pouring melted metal upon the back of the congeries; and the present method, as is well known, is, after having set up the types, to take an impression from them in plaster of Paris, or some other composition, and to cast or found the plate in this as a mould. It does not very clearly appear what was the plan which Canstein followed; but it is known that he printed a great many volumes and sold them very cheap. A copy of the New Testament, for instance, he used to sell for fourpence; but, as he was very pious, it is not improbable that he distributed the Scriptures at less even than the cost price, which his fortune enabled him to do. It is said that it was while endeavouring to devise a cheap method of multiplying copies of the Bible for the use of the poor, that the notion of his invention suggested itself to him.

CHAPTER XXVIII.

SELF-EDUCATED CULTIVATORS OF SCIENCE:-PARKES; DAVY.

MOST of the individuals we have mentioned, who, born to rank and affluence, have devoted themselves to scientific pursuits, were enabled to accomplish what they did, in a great measure, from the peculiar advantages of their position, which afforded them both leisure for the

prosecution and maturing of their several schemes, and money to expend on the necessary apparatus and experiments. This proves to how much profit the rich man may turn his fortunate external circumstances, even in the pursuit of knowledge, if he can only rouse himself to enter with earnestness upon that enterprise. But still the ambition of aspiring minds, left to struggle unassisted by such external aids, has accomplished, after all, quite as great things as all the resources and immunities of what might be deemed the happiest worldly lot have ever given birth to. We now return to accompany for a while the onward steps of a few more of those courageous adventurers, who have begun and carried on the work of mental cultivation, without heeding any combination of worldly disadvantages against which they might have to contend. We shall begin with the cases of one or two individuals so situated, who have distinguished themselves in that same field of experimental science in which we have just seen what Boyle and Cavendish achieved in their very opposite circumstances.

The first name we shall mention is that of one who has no claim, we believe, to any important discovery in the department which he cultivated, but whose literary works, nevertheless, as well as his history, abundantly testify him to have been a most ingenious and meritorious man. We speak of the late MR. SAMUEL PARKES, the well-known author of the "Chemical Catechism." Mr. Parkes, as we learn from a communication with which we have been favoured by his surviving daughter, was born in 1761, at Stourbridge, in Worcestershire, where his father was a small grocer. At five years of age he was sent to a preparatory school in his native town; and it is remembered that, during the time of his attendance at this infant seminary, Mr. Kemble's company of itinerant players having visited Stourbridge and remained there for some months, that gentleman placed his daughter at the same school, the child who became afterwards the celebrated Mrs. Siddons. When ten years old, Parkes was sent to another school at Market Harborough; but, after remaining here only a very short time, he was taken away and apprenticed to a grocer at Ross, in Herefordshire. This person happened to be a man of some education, and to be possessed of a few books, which he very kindly lent to his apprentice; but, although he endeavoured to give him a taste for reading, he could not, it is said, gain much of his attention. It does not appear how long young Parkes continued in this situation; but at last his master failed, and he returned home to his father. We now hear no more of him till he had reached his thirty-second year, up to which time, it seems, he remained at home, assisting his father in the shop. It is probable, from the resources he afterwards displayed, that the foundation of many of his acquirements was laid during this interval. Perhaps he had also saved a little money; for he now went to Stoke-upon-Trent, began business on his own account

as a soap-boiler, and married. The new line upon which he entered shows that he had been already directing his attention to practical chemistry. But, after persevering for ten years in this business he met with so little success as to be obliged to give it up; and at the age of forty-two he came up to London with no property in the world, except ten pounds, which had been lent him by his father. It was hard enough to be obliged, as it were, to begin the world again at this time of life; but there was no help for it, and he set to work resolutely. Some friends whom he had made lent him a little assistance, and he began manufacturing muriatic acid for the use of dyers. It is very evident, that, although he had come to town without much money in his pocket, he had brought with him some useful knowledge-one fruit, at least, of the labours of his previous life, of which fortune had not been able to despoil him. This he now turned to excellent account. To his muriatic acid he soon added other chemical preparations, his skill in manufacturing which was not long in being generally appreciated, and eventually procured him a large trade and a high reputation.

Although Mr. Parkes had probably given considerable attention to some of the practical parts of chemistry before he came up to London, it was only after he had established himself in this last-mentioned line of business that he began to study the subject scientifically. At this time, as we have seen, he was above forty years of age-so that he may be quoted as another most encouraging example for those who have been prevented by any cause from commencing their studies till late in life. Notwithstanding the time he had lost, Mr. Parkes became eventually a most accomplished chemist, and gave to the world a succession of works relating to that science which long continued to hold the rank of textbooks of high authority. The earliest of these was his "Chemical Catechism," which first appeared in 1805. It was translated, soon after its publication, into the German, French, Spanish and Russian languages. By this work alone, of which numerous large editions were printed, the author realized 5000l. The Catechism was followed by another work, “The Rudiments of Chemistry;" and that by the “Chemical Essays,” in five volumes. This last in particular, is an excellent performance, and strikingly shows the author's extensive acquaintance with his subject. Like their precursor, these two works were also translated into the principal continental languages, and obtained great popularity abroad, as well as in this country. Among other gratifying testimonies which the author received of the sense entertained of his labours, was a splendid ring presented to him for his services to science by the Emperor Alexander I. of Russia.

One of the chief merits of the elementary works published by Mr. Parkes, and what must doubtless more than anything else have helped to make them popular, lies in this; that in all his explanations the

author begins at the beginning, and nowhere assumes any information necessary for understanding the subject, to exist in the mind of the reader beyond what he has himself communicated. It might seem, at first sight, as if this were a part of the art of teaching of no very difficult attainment. Yet the fact is, that it is a secret of which very few writers have made themselves masters. In general the person who resorts to a professedly elementary treatise, in order to study any branch of science of which he previously knows nothing, finds himself stopped before he has gone very far, by the author paying him the very inconvenient compliment of addressing him as if he were familiar with many things of which he is quite ignorant. Hence, more than on any other account, the uselessness, or at least the insufficiency, of the greater number of such works for the end which they are intended to serve. They almost always suppose the reader to know, before he opens them, no inconsiderable part of the very mystery which they profess to teach. It sometimes, no doubt, happens that the reader does accidentally possess this requisite preliminary information; and then (though no thanks to the author) he will make his way through the book without being inconvenienced by its deficiencies. In other cases he may have sufficient ingenuity to deduce from what is stated some conjecture more or less vague as to what is passed over, and in this way may be enabled to proceed in his perusal without finding himself absolutely in the dark. But his progress, so conducted, is not only slow, unsatisfactory, and painful, compared to what it might be, but is likely besides to leave him at last only half-informed or misinformed as to many things which he supposes himself to know. Perhaps the best way of employing books of the description to which we allude-when no better are to be had-is for the student to provide himself with two or more at the same time upon the subject of which he wishes to make himself master; so that, when he finds one deficient or unintelligible, he may have a chance of finding an interpreter in another. This is a method which has sometimes been successfully followed by persons who have been obliged to be their own instructors, after every attempt to understand the science, or other branch of education, which it was desired to learn by the assistance of a single author, had proved a failure; and we recommend it to others similarly situated. The probability is, that of two writers each of whom at times expresses himself obscurely, the one will not always or usually fall into that fault in regard to exactly the same matters as the other; and, therefore, though either alone might be an inadequate instructor, the two together may shed sufficient light on the subject. Besides, of two or more ways of presenting or illustrating the same truth, one mind is most readily reached by one, and another by another; so that, even when no absolute insufficiency can fairly be complained of in either treatise, the two are still better than one. The

force of this last consideration has induced some popular writers of elementary works to state the more difficult parts of their subject in a variety of ways, for the sake of more surely impressing them upon the various minds, or moods of mind, they may chance to address; and the practice, when followed judiciously, and so as not to overload the book with unnecessary repetitions, a course which only fatigues the reader and distracts his attention, is one which may be made greatly to contribute to the clear and effective exposition of the author's meaning.

It may seem strange that so many writers should have failed in the observance of a rule of elementary explanation apparently so simple and easy as that in question. What less difficult, it may be said, or even more natural, than, in expounding any subject to a mind which is supposed to be ignorant of its first principles, to state everything with a recollection of, and in accommodation to, that ignorance? It is only, in the first place, to deduce the introductory statements from sufficiently familiar instances, and then, in pursuing the line of inference or demonstration, to advance from one thing to another by sufficiently short steps. But even to do this requires no common degree of attention, patience, and skill. It is true that all science, even the highest and most recondite, is deducible from the facts or feelings of ordinary life; but it often happens that a proficient in a particular science has never viewed it in this connection. The manner in which he was himself taught it did not lead him to do so. He was probably carried through what were called its principles, by an exercise of his faith rather than of his reason; and left to gather a full understanding of them, not so much from what he knew of their foundations before, as from what he was to see of their application afterwards. He was like a man entering a half-darkened apartment, to whom everything is at first invisible, and who is indebted for the measure of discernment which at last enables him in some sort to distinguish objects, not to any additional light which is thrown upon them from without, but to the expansion of eye which the dimness itself occasions. It may happen that, in the progress of his studies, his partial acquaintance with one part of the subject has so much aided his partial acquaintance with another part, that he has at last attained to a tolerably clear notion of the whole. But still it remains in his head an insulated system of propositions, altogether withdrawn and separated from those truths of ordinary experience out of which, nevertheless, it has wholly sprung. When a person, therefore, who has acquired his knowledge in this manner sits down to write an elementary book, he will be very apt to overlook that connection between scientific and common truths to which his own attention has never been called. He will begin his treatise, not by reference to something which is understood by everybody, but by an announcement so far ahead of everything of this kind, that its meaning is likely to be