Such is the information to which I have been led by the examination of the Canada thistle. In addition to the practice of frequent mowing and spudding, as the best means of destroying this weed, I would suggest the following system of culture :

1st. After deep and frequent ploughing, to occupy the ground with corn, potatoes, or some other crop which will require frequent hoeing and clearing.

2d. In the autumn, after taking off the crop, again to give the land another deep ploughing, leaving it in the rough state, so as to expose the roots of the thistle to the frost of the ensuing winter: this process will also the better prepare the soil to be laid down in grass the following spring. In doing this I would also suggest the propriety of

3dly. Sowing a much greater quantity of grass seed to the acre than is usually done. By pursuing the practice recommended by Lord Kames, of sowing from twenty to twenty-four pounds of clover seed to the acre, I have remarked that the grounds at the Elgin Botanic Garden are much more free from weeds than those of my neighbours, at the same time that the grass is much more delicate for feeding, less apt to be thrown down by the storm, and makes a less succulent hay, both more easily cured and better preserved than where it is more thinly spread, but of stronger growth. How far these may prove additional means of counteracting the growth of the thistle in question, I submit to you and other practical farmers. I am sir, yours, &c.

HON. S. L. MITCHILL.

DAVID HOSACK.

REVIEW.

ART. I. A Plain Elementary and Practical SYSTEM of NATURAL EXPERIMENTAL PHILOSOPHY; including Astronomy and Chronology. By the late JOHN EwING, D. D. Provost of the University of Pennsylvania. Being the course of lectures, delivered by him in that Seminary (enlarged and improved from time to time) for upwards of twenty years. Illustrated by copperplate engravings. The whole carefully revised and prepared for the press, with sundry explanatory and supplementary Notes, by ROBERT PATTERSON, Professor of Mathematics in the said University: with a Biographical Sketch of the Author. Philadelphia, Hopkins and Earle, 8vo. pp. 563.

DR. JOHN EWING was born in East Nottingham, Maryland, on the 22d of June, 1732. He commenced his classical studies under the care of the late Francis Allison, D. D. with whom also, he afterwards made considerable progress in the science of mathematics. The ardent zeal he possessed for scientific pursuits overcame every difficulty, and from his books and the conversation of his affectionate preceptor, he acquired a habit of close thinking, for which he was ever after distinguished. In 1754 he removed to the College of Princeton where by his persevering industry he became a favourite pupil of President Burr. In 1765 he took the degree of A. B. and finding himself restricted in his pecuniary circumstances, he accepted the appointment

Ee

of tutor in the college. About this period he resolved to choose a profession, and theology being most congenial to his turn of mind, he entered upon that study under the direction of his former friend and preceptor, the Rev. Dr. Allison. At the age of twenty-six he was employed to instruct the philosophical classes in the college of Philadelphia, during the absence of the provost, the late Dr. W. Smith. In 1759 he accepted an unanimous call from the first presbyterian congregation in Philadelphia, of which he continued a minister until his death.

From the year 1759 to 1773, he dicharged his duties with a diligence and zeal not often surpassed. During this period his studious researches enabled him to collect materials for the compilation of his Lectures on Natural Philosophy. In 1773, he was commissioned, in conjunction with Dr. Hugh Williamson, to solicit subscriptions in Great Britain, for the academy of Newark, in the state of Delaware. In all the several places he visited in England, Scotland, and Ireland, he met with a cordial reception from gentlemen of the most distinguished reputation. In the summer of 1775, at the commencement of the revolution, he returned to America, though he was earnestly solicited to remain in England, and liberal proffers made to him for that purpose. In 1779, he was elected provost of the university of Pennsylvania. On his appointment, he prepared the lectures which are now published, and which he delivered during a period of twenty years. He was one of the founders and a distinguished member of the American Philosophical Society, to which he contribu ted several valuable papers. To the astronomical articles of the Encyclopedia published by Dobson, he made many additions. In the year 1795 he undertook the com

pilation of a course of lectures on natural history; but owing to his imperfect health, was unable to complete his plan. He died in September 1802. Dr. Ewing was an eminent proficient in mathematics, astronomy, and every branch of natural philosophy. In the Latin, Greek, and Hebrew languages his knowledge was very considerable; in logic, metaphysics, and moral philosophy, one of the most accurate and profound of scholars.

From the life of Dr. Ewing, which we have extracted, chiefly from the interesting memoir prefixed to the work, we enter upon an examination of the subject matter of

the volume.

This system of philosophy is preceded by an introduction, in which are first briefly mentioned the difficulties which have obstructed the progress of natural science. These were caused principally by the desolations of war, the hypothetical methods of philosophising, and the superstition and selfish views of the priests. Our author next remarks on some of the more important events which have contributed to the present free and rational method of investigation, and to the consequent advancement of knowledge. The most important of these was the reformation in religion. About the year 1640, Descartes published his philosophy, in which he maintained, that nothing was to be received upon mere authority. "Although he carried the humour of doubting somewhat too far," Dr. Ewing," and admitted only of the self-evident proposition, I think, therefore I am, he has the honour of introducing a more safe and liberal method of philosophising and thereby of paving the way for all the discoveries that have since been made in physics." This encomium bestowed on Descartes, appears to us to belong with equal

says

propriety to Bacon. Indeed, Dr. Ewing does not seem to have duly appreciated the stupendous labours of that extraordinary man. While to Descartes is attributed the superlative honour of having drawn a distinct line between the material and the intellectual world, and of having destroyed the power of the Aristotelian sect, Bacon is acknowledged as the father of experimental philosophy. At the time too, when the several productions of Descartes were offered to his countryman, the works of Bacon were making their way throughout the learned world, and that lasting monument of his fame, the Instauration of the Sciences, had already begun to effect a revolution in the empire of science, and to lay the foundation of natural knowledge on the sure basis of fact and experiment.

Of the investigations of Galileo. Dr. Ewing speaks in terms of commendation, and of the discoveries of Sir Isaac Newton, in language bold and decided. The introduction closes with some appropriate reflections on this branch of human learning.

The lectures commence with a general definition of natural philosophy, which is followed by the Newtonian rules of philosophising. The common and universal properties of matter are next detailed, and the several kinds of attraction explained. Succeeding the remarks on capillary attraction are some observations which we shall take the liberty of transcribing, as we were somewhat surprised that Dr. Ewing should have found a ready solution to several phenomena which have hitherto remained inexplicable to other philosophers.