The mutual opposition of the leading philosophical sects of antiquity had, in general, most fatally dis couraged the application of mathematical reasoning to the system of the material world. The Academi• clans, or the disciples of Plato, who cultivated geome try with ardour and brilliant success, were disposed to regard that science as a pure intellectual contempla tion ; and resigning themselves to the illusion of their lofty dreams, they turned with disdain from the in vestigation of individual facts and all the vulgar realities of life. The mind of Aristotle was of a more sober and practical cast ; acute, profound, and discriminating, it ranged, with incredible indus try, over an immense field of inquiry. That judi cious philosopher recommended a careful and con stant appeal to external observation, as the only sure ground on which to erect the structure of physics ; but unfortunately his scholars neglected too much the study of mathematics, the most powerful instru ment for conducting physical research. The pre cepts of Aristotle, though excellent in some re spects, were hence in the sequel unproductive of any genuine fruit. On the contrary, the weight of his opinions, during a long course of ages, confined and repressed the efforts of human genius.
It must be gratefully acknowledged, that the alche mists, styled also philosophers by fire, were the first among the moderns who dared to explore new paths of science. Their projects were, indeed, highly chimeri cal, but they had the merit at least of setting the ex ample of investigating the properties of matter by ac tual experiment. They likewise formed associations among individuals, for the more effectual prosecution of such researches. Hence the origin of that obscure sect, known by the fanciful title of Rosicrucians, who sprung up in Germany, and insensibly spread their Influence over the Continent. Those princi ples were afterwards transplanted into the matur ed soil of Italy, where philosophy, succeeding to the cultivation of letters, wore a more attractive garb. Baptista Porta, a Neapolitan nobleman, who flourished about the latter part of the sixteenth cen tury, was especially distinguished by his zeal in pro moting such pursuits. Having spent many years in travelling over _Europe to gain information respect ing natural objects, he invited a few individuals of a similar taste to assemble, at stated times, in his house, and assist him in making new experiments. These meetings, however, gave umbrage to the watchful jealousy of the clergy, and they were soon sup presd by a mandate from the Court of Rome. But the example was imitated in other parts of Italy, where the papal authority enjoyed less respect ; and academies, for the promotion of natural science,_ were successfully instituted under the patronage of different princes, particularly those of the illustrious house of Medici..
In this ferment of inquiry, Galileo arose, a man fit ted alike by the gifts of nature, and the lights of edu cation, to be the founder of experimental science. His elegant genius was invigorated by the study of the Greek geometry ; and he conceived the happy and prolific idea of employing that refined instrument to explore facts and combine the results. Archimedes, indeed, among the ancients, had anticipated this road of discovery, having most successfully applied the powers of geometrical analysis to the investigation of some parts of mechanics and hydrostatics. But his was a solitary instance, unheeded by succeeding ages. The ingenuity of Galileo prepared a com plete revolution in science. By means of a few simple but striking experiments performed on the lagoons of Venice, he established the laws of motion, which he now transferred from the surface of our globe, to direct the revolutions of the heavenly bodies. The publication of his Dialogues, which unfold the right process of induction, and are not less distinguished by fineness of conception than beauty of diction, form a new era in the annals of philosophy. He was the first that attempted to as certain the weight of air by actual experiment ; and considering the nicety of the operation, and the rudeness of the instruments constructed at that period, he made a very tolerable approach to the truth. It had been known for many ages, that air is capable of being highly condensed ; andCtesebius of Alexandria had invented an engine, which, by the force of the sudden expansion of this compressed fluid, hurled mis sile weapons. This was afterwards improved into the wind or air-gun, which seems to have been not un common in Europe as early as the fifteenth century, though soon afterwards generally superseded in prac tice by the introduction of fire-arms. Galileo, being . led by a different path from that pursued at present, set himself to examine the weight which air acquires by condensation. Having fitted a large copper vessel with a valve, he injected air into its cavity by means of a syringe, and then suspended it to a balance. The additional increase of weight being thus found, he opened the valve under an inverted glass receiver full of water, and measured, by the displacement of this liquid, the surplus quantity of air which had been injected into the copper vessel. He thence concluded that air is 400 times lighter than water, being about the double of the true estimate.