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.

Most of the individuals we have here 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 enterprize. But still the ambition of aspiring minds, left to struggle unassisted by such external aids, has achieved, 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, and endeavoured to give him a taste for reading, but 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, ever since their publication, have held the rank of text-books of high authority. The earliest of these was his Chemical Catechism,' which first appeared in 1805, and of which twelve very large impressions have since been sold. It was translated, soon after its publication, into the German, French, Spanish,

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and Russian languages; and in Spain and Germany it is the standard manual of instruction in the public schools. By the sale of this work alone the author realized 50001. The Catechism was followed by another work, The Rudiments of Chemistry;' and that by the Chemical Essays,' in five volumes. This last, in particular, of which a new edition has lately appeared, 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 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 no where 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, a 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,

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 instructers, 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, cach 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 ina