phenomena are regulated. Happily for the world, the Stagyrite and his categories, the Cartesian vortices of more modern times, and all the intermediate absurdities and metaphysical subtleties no longer haunt the imagination of the philosopher. The sagacious mind of the illustrious Bacon, with his inductive process, brake through the trammels of the schools; and the sublime genius of Newton, with his scientific investigations, has conducted the student of Nature from the dark and intricate mazes of uncertainty. and error into that illumined path which leads through nature.

up to nature's God."

An immense field of accessible knowledge is therefore spread before us; and perhaps one of the greatest advantages which we can derive from contemplating the universe is the view which true philosophy affords us of the perfect harmony and admirable subserviency of all its parts in promoting the beneficent purposes of its Divine Author. Let us not listen then to the fear-fraught admonitions of those who would shrink from the study of Nature with a kind of superstitious horror, and represent the men who attempt to investigate her general laws as lifting their puny arms* against the Almighty Governor of the universe, or plunging into the dark abyss of Atheism. For, so far is this from being a legitimate consequence of true philosophy, that those who have madeit most their study, have found at every step the most striking instances of incomprehensible wisdom, and continually perceived, that He who ordained the general laws of Nature saw at once their remotest and most minute consequences, and adjusted the vast assemblage to answer every purpose of His Providence. With these views, the philosopher hesitates not to adopt the sentiments of one of the most earnest inquirers into the works of creation; and who exclaims with rapture, "This universe is the magnificent temple of its Great Author, and man is ordained, by his powers and qualifications, the high priest of Nature, to celebrate divine service in this temple of the universe."

We have been led into these reflections by the work before us, but shall now endeavour to atone for indulging in them by confining ourselves strictly to the work itself. The title of these volumes implies their being more particularly designed for those who attend the Lectures delivered by the learned Professor; but as he has submitted them to publication, we conceive that a brief explanation of his design is due to the public. However, as he has thought it right to leave individuals to form their own judg ment, we shall endeavour to assist them in doing so, by stating the general nature and contents of the work; illustrating our cursory observations by a few extracts.

The method which the Professor has adopted is that of proposi

tions, frequently accompanied by historical notices, elucidatory remarks, and practical results; and references to the principal works containing their demonstrations are generally subjoined. With regard to these extracts, our wish is to accommodate them, as much as possible, to our general readers; because we are convinced that our respect cannot be more fully shown either to the learned author himself, or to our scientific friends, than by advising the latter to peruse the work attentively, and judge for themselves.

The subjects included in the first Volume are, 1. The INTRODUCTION, Containing definitions of the principal terms employed in the science, and an explanation of the properties of matter. 2. DYNAMICS, including measures of motion, first law of motion, communication of motion by impulse, motion equally accelerated or retarded, motion of projectiles, and motion accelerated or retarded by variable force. 3. MECHANICS, in which are considered the centre of gravity, the mechanical powers, friction, mechanical agents, motion of machines, descent of heavy bodies on plain and curved surfaces, and the rotation of bodies. To this head an Appendix is subjoined containing the construction of arches, and the strength of timber. 4. HYDROSTATICS, under which the Professor treats of the pressure of fluids, solid bodies floating on fluids, and the phenomena of capillary tubes. 5. HYDRAULICS, under which, fluids issuing through apertures in the bottom or sides of vessels, conduit pipes and open canals, percussion and resistance of fluids, undulation of fluids, or the formation of waves, and hydraulic engines are treated of. 6. AEROSTATICS, comprising heat, and equilibrium of elastic fluids. 7. PNEUMATICS, in which air is considered as accelerating or retarding motion, as the vehicle of sound, and as the vehicle of heat and moisture. Wind and rain are also included in the topics of consideration.

The Second Volume consists of ASTRONOMY, and is divided into two parts. Part I. treats of the fixed stars and the circles of the sphere, atmospherical refraction, figure of the earth, geographical problems, parallaxes, motion of the sun, motion of the moon, eclipses, planets, secondary planets, comets, aberration of light and the nutation of the earth's axis, dimensions of the solar system, the annual parallax, and the distance of the fixed stars. To this part an Appendix is subjoined, treating of the method of determining by observation the constant coefficients in an assumed or given function of a variable quantity. Part II. PHYSICAL ASTRONOMY. In this part Professor Playfair treats of the forces which retain the planets in their orbits; those which disturb the elliptical motions of the planets; disturbance in the motions of the primary planets, from their action on one another; disturbance

in the motion of the satellites of Jupiter, from their action on one another; general result from the theory of planetary disturbances; attraction of spheres and spheroids; figure of the earth; precession of the equinoxes; variation of the obliquity of the ecliptic; explanation of the phenomena of the tides; and the principle of universal gravitation.

The following extracts, selected from the article on mechanical agents, show the manner in which this able writer applies the result of his philosophical investigations to the practical purposes of life.

The strength of men, and of all animals, is most powerful when directed against a resistance that is at rest: when the resistance is overcome, and when the animal is in motion, its force is diminished; lastly, with a certain velocity, the animal can do no work, and can only keep up the motion of its own body. A formula having the three properties just mentioned, will afford an approximation to the law of animal force. Let P be the weight which the animal exerting itself to the utmost, or at a dead pull, is just able to overcome; W any other weight, with which it is actually loaded; and v the velocity with which it moves when so loaded; c the velocity at which the power of drawing or carrying a load entirely ceases; then W=P (1) is an equation that has all the three conditions mentioned above. Not only, however, has the formula P (1) these conditions, but the square of it has the same, or indeed, any function of it which vanishes when (1-) vanishes, that is, when v=c. We are left, then, at liberty to choose any of these functions, and would assume the formula above as the simplest, if another condition did not seem necessary to be included. It is certain, that in all cases, when v approaches to c, or when the speed becomes great, a small variation in the weight is accompanied with a great variation in the velocity. The simplest formula that corresponds to this condition, is, when 1-is raised to the square.

C

Therefore, till experience has led to a more accurate result, we may suppose the strength of animals to follow the law expressed by the formula W=P (1) Vol. I. p. 105.

2

He then states the following conclusion with respect to the greatest quantity of work that can be done by an animal in a given

time.

The effect of animal force, then, or the quantity of work done in a given time, will be proportional to Wv, or to Pv (1-), and will be a maximum wheṇ v=-and when W= and when W, that is, when the animal moves with one third of the speed with which it is able only to move itself, and is loaded with four-ninths of the greatest load it is able to put in motion. p. 106.

Mr. Playfair then applies the same formula to the motion of machines as follows;

If, therefore, the moving power in any machine follow the law expressed by the equation WP (1-2); and if the load or resistance that is just able to keep the machine at rest, or to prevent its motion altogether, be found by experiment; then if the load be reduced to of this quantity, the effect of the machine will be the greatest possible. The moving power and the resistance being both given, other things remaining as above, if a machine be so constructed, that the velocity of the point to which the power is applied, be to the velocity of the point to which the resistance is applied as 9 R to 4 P, the machine will work to the greatest possible advantage. p. 118.

We regret that our limits do not permit us to extract the whole of the Professor's very ingenious explanation of the trade winds, which we regard as more satisfactory than any thing we had previously seen on the subject, and think it could not have failed to afford information to most of our readers. He justly considers the general motion of the air, near the earth's surface, as from the poles towards the equator, and then combines the effect of these currents with that of another motion in the following perspicuous and satisfactory manner.

In consequence of the rotation of the earth on its axis, another motion is combined with that of the currents just described. The air, which is constantly moving from points where the earth's motion on its axis is slower, to those where it is quicker, cannot have precisely the same motion eastward with the part of the surface over which it is passing, and therefore must, relatively to that surface, describe a curve, having its convexity turned to the east. The two currents, therefore, from the opposite hemispheres, when they meet toward the middle of the earth, have each acquired an apparent motion westward, and as their opposite motions from south and north, must destroy one another, nothing will remain but this motion, by which they will go on together, and form a wind blowing directly from the east.

p. 294.

The second volume of these "Outlines," is a very valuable epitome of Astronomy, in which the Professor's extensive knowledge, perspicuity of explanation, and solidity of judgment, are repeatedly discovered. We should find no difficulty in producing extracts to justify this assertion, did our limits permit. Our restrictions, in this respect, however, are of less importance, as the size of the volume renders it easily accessible to all who feel interested either in the results, or in the objects of contemplation which this science presents. We shall, therefore, confine ourselves to the two following. The first we select as one out of numerous instances of the practical utility of astronomy; and seriously recommend it to the

candid consideration of those, who, at the very time they are deriving so many advantages from the more sublime branches of science, represent them as mere speculations, unconnected with the affairs of life, and consequently as only fit for the recluse or the misanthrope. The latter passage we should be glad to see indelibly impressed on the minds of those, who talk as though the universe had been formed by the fortuitous concourse of inanimate atoms.

As the true length of the sun's revolution is not what has now been supposed, but instead of 365. 25, is only 365d. 242264, the Julian year is longer than the revolution of the sun by Od. 007736, (nearly 11m;) and, therefore, before a new year begins, the sun has passed the point in the ecliptic where the last year began, by a small fraction, viz. 007736 X 59′ 8". The Julian reckoning, therefore, falls continually behind the sun, and the course of the seasons, by a quantity which however was so small, that it was long before it was observed.

At the time of the Council of Nice, in the year 325 of the Christian æra, the Julian calendar was introduced into the church; and at that time the vernal equinox fell on the 21st of March. On account of the imperfection in the mode of reckoning just noticed, the reckoning fell constantly behind the true time; so that in the year 1582, the Julian year had fallen nearly 10 days, (9.72415) behind the sun and the equinox, instead of falling on the 21st, fell on the 11th of March; so that the difference was nearly a day in 132 years. The continuance of this erroneous reckoning would have made the seasons change their places altogether; and it was therefore resolved to reform the Kalen. dar, which was done by Pope GREGORY XIII, and the first step was to correct the loss of the ten days, by counting the day after the 4th of October, 1582, not the 5th, but the 15th of the month."

As the loss in the Julian Kalendar amounted to one day in 132 years, it would amount to three in 396 years, or in the space nearly of four centuries. It would be necessary, therefore, supposing the Julian intercalation to continue, to suppress three intercalary days in the course of four centuries; and it was agreed, that this should be done on the three successive secular years, retaining the intercalary day on the fourth, by which means the sun, at the beginning of the fifth century, would occupy the same point in the ecliptic, within a few minutes, that he did at the beginning of the first. p. 109–111.

The second extract above referred to occurs at the conclusion of the section on the disturbance occasioned by the mutual action of the planets on each other.

One general result of these investigations is, that both in the system of primary and secondary planets, two elements of every orbit remain secure against all disturbance; the mean distance, and the mean motion, or which is the same, the transverse axis of the orbit, and the time of the planet's revolution. Another result is, that all the inequalities in the planetary motions are periodical, and observe such laws that each of them, after a certain time, runs through the same series of changes.