and imagined the crystalline lens to be the part in which it is formed. In one passage he has been interpreted as anticipating the discovery of the telescope, but an attentive examination clearly shows that his words will not fairly bear any such construction. He mentions the reflection of cold at the focus of a concave speculum, which is estimated by using the eye in the place of a thermometer. This very singular suggestion would seem to imply a greater advance in speculations on the nature of heat than we can suppose to belong to this age. It does not clearly appear whether this method was ever actually tried, or is a mere suggestion; nor at this day are we aware of any thing being known which can clear up the point.

Though much of the “ Magia Naturalis” is devoted to experiments and contrivances of a frivolous nature, yet it exhibits a close acquaintance with scientific principles. The work became very popular, and was translated into several languages. The general disposition of the age was now more favourable to the dissemination of knowledge, and the facilities afforded by the rapid multiplication of books, were beginning to be productive of the best effects in enlightening the public mind. Porta also was personally popular, and his house became the resort of the curious and learned; but all this awakened the jealousy of the church; and not only the works of the Neapolitan philosopher, but even his private parties became objects of suspicion to the ecclesiastics. We do not, however, find that they proceeded to any direct acts of persecution; perhaps their victim had the caution to give them no occasion for doing so.

Dr. Gilbert, of Colchester, published a work on magnetism in 1590, which contains a copious collection of valuable facts and ingenious reasonings. He may be said to have laid the foundation of our knowledge in this department of science, which has since opened into so many new and important analogies.

He extended his enquiries, also, into the kindred

subject of electricity, and made many new experiments on its developement by excitation in different substances. The declination, or deviation of the needle from the true north, was observed by Sebastian Chabot, and the dip by William Norman before this period.

Though not, perhaps, directly concerned in physical science, yet, as a vigorous opponent of the Aristotelian system, which placed such formidable obstacles in the way of the advance of experimental enquiry, we may here notice the labours of the celebrated Peter Ramus, who was born in 1502, and subsequently became a professor of philosophy in the university of Paris. In this situation he strenuously contended against the scholastic dogmas which placed such pernicious restraints on the energies of the human mind, and so grievously impeded the progress of truth. Such conduct, of course, drew down upon him the hostility of the heads of the university; and before a tribunal, which they obtained to be appointed under royal authority, he was tried and condemned. His enemies appear to have exulted in their triumph; but his friends were sufficiently influential to obtain for him another professorship; and his powerful eloquence seems to have been again employed with great effect in opposing the Aristotelian tenets. The unsettled state of the country, however, greatly interfered with all philosophical pursuits; and Ramus, after many sufferings, perished in the massacre of St. Bartholomew, 1571.

Jerome Fracastor, about 1540, published a treatise "De Stellis," in which he distinctly refers to the principle of the resolution of motion; observing, that bodies, having a tendency to fall straight to the centre of the earth, when thrown transversely to that direction take an intermediate course.

We have seen, in a former section, that the lever was the only one of the mechanical powers whose theory was perfectly established by the ancients. The equili brium of bodies, consequently, could only be successfully

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investigated in cases which were reducible to this. We have also observed, that the doctrine of the inclined plane was unsuccessfully attempted by Pappus. No further investigation appears to have been tried till the sixteenth century, when Cardan considered the problem in a more distinct light; though what he advanced on the subject was no more than a plausible conjecture.

Guido Ubaldi, an Italian mathematician, also attempted the problem of the oblique action of forces with imperfect success in 1577. He considers chiefly the wedge; and comparing the direction in which it tends to produce motion with the direction in which the body thus acted on really moves, he observes that there is between these directions " a certain repugnance," which is greater as the angle of the wedge is more obtuse. He hence infers that the wedge will produce its effect the more easily the more acute it is, but without obtaining the exact proportion of the force. He also observes rightly, that the screw may be considered as a wedge wrapped round a cylinder.

It has been stated that the problem of the inclined plane had been solved by Jordanus in the thirteenth century, and that the solution is given in Tartalea's edition of his works in 1565. The discussion, however, is so vague and obscure, and so mixed up with the peripatetic views, that it cannot be admitted as having a valid claim to be a real demonstration.

The individual who really first solved the problem of oblique forces on solid principles, was Simon Stevin of Bruges, whose works were published soon after 1600. He not only deduced correctly the ratio of the power to the weight on the inclined plane, but, on the same principles, resolved forces so as to obtain their effect in different directions, and solved a number of important problems relating to them. The principle of his reasoning was highly original and simple. He supposed a perfectly flexible, uniform chain, joined at its ends, and hanging upon the inclined plane down its perpendicular side, and in a festoon below. However free the mo

tion upon the plane, he conceived this chain will always sustain itself at rest; the part below cannot affect its motion. Hence the parts on the plane and in the perpendicular support each other, and their weights are proportional to those lengths respectively.

These investigations entitle Stevin to be regarded as the father of modern statics. After the inclined plane had thus been investigated, various other authors completed the different parts of the subject by following up the conclusions resulting from the principle of resolution of forces.

To Stevin we likewise owe the first suggestion of the fundamental principle of hydrostatics, that the pressure of fluids is in proportion to their depth.

The rainbow had from the earliest times been an object of admiration to every spectator, but it was long before any observer knew the full extent to which that admiration ought to be carried, or even cared to understand it. If it be unpardonable to shut our eyes to the most glorious spectacles in nature, it is doubly so to close our mental vision against that more perfect and more intimate perception of them, which the knowledge of their causes affords.

Among those who felt any interest in such enquiries, the rainbow was generally understood to arise in some way from the light reflected by the drops of rain falling opposite to the sun.

Maurolycus suggested that the light in passing through the drop, so as to be reflected from its back, somehow acquires colour from the refraction. But he proceeded no farther with this idea. Others made suggestions which only tended to perplex the matter.

Antonio de Dominis, archbishop of Spalatro, approached very nearly to the complete explanation. Having placed a globular bottle of water opposite to the sun, and above his eye, he saw coloured rays issue from the under side of the globe; the colours were different, according as it was more or less elevated; and in the order of the rainbow. He correctly traced the course of

the rays refracted at entering and quitting the water, and reflected at the back of it. The same would, therefore, hold good with a globular drop of water in a shower; and, from the same angle being invariably required for each colour in a plane passing through the eye, the drop, and the sun, the circular form of the bow was accounted for. Still, the actual origin, or law of the connection between refraction and colour was totally unknown. The explanation, too, extended only to the primary or interior bow: in attempting that of the secondary, the author failed. This investigation of De Dominis is the more remarkable, since he is not known for any other scientific discovery; he published an account of it in a work, "De Radiis Visus et Lucis," in 1611. Yet the treatise is in some points so faulty, that Boscovich calls him " homo opticarum rerum supra' id quod patiatur ea ætas imperitissimus,” (a man ignorant of optics to a degree even beyond what that age would endure). This seems unduly severe upon a man who had been the first to propose an explanation so perfectly just and philosophical, as far as it went, of a very complex phenomenon. And if deficient in some points of detail, yet he certainly possessed a philosophical love of truth; which was evinced in a freedom and independence of opinions on theological subjects, extraordinary to be avowed by a dignitary of the Romish church: and which, as he had not the hypocrisy to disguise it, was, of course, heresy, and exposed him to a furious persecution. From this he found an asylum at the court of James I. of England, in 1616. But, returning to Italy, the persecution was, after some time, revived, and he died, as is supposed by poison, in prison; his body, and all his writings, being condemned to the flames by the Inquisition.

Copernicus.

Nicolas Copernicus was born at Thorn in Prussia, in 1473. In the university of Cracow, he attained considerable proficiency in the mathematical sciences; and, incited by a laudable emulation of the fame then obtained