The Hydrometer is an instrument for admeasuring liquids; by it the strength or specific gravity of different fluids is discovered, by the depth to which it sinks in them. It has been chiefly used for discovering the contents of different salt waters, without analysis, and is now almost entirely used by persons connected with the spirit-trade, to ascertain the different degrees of strength, and what alloy they will bear; hence its utility to the manufacturer and the excise-officer is apparent.

The laws respecting the comparative weight of different fluids, as well as of solid bodies immersed in them, was first discovered by that great geometrician Archimedes. It may be far from improbable that Archimedes constructed that instrument himself; and if it should appear that he did, it must have happened two hundred and twelve years before the Christian era.

The most ancient mention of this instrument by its specific name, occurs in the fifth century of our era, upon the following occasion. The anecdote is very singular and affecting, and also evinces the incapacity of humanity to act consistent and as it ought, when we suffer ourselves to be directed by passions unworthy of the human character.

It is first discovered in those letters of Synesius to the philosophic and beautiful Hypatia. We trust we may be excused the liberty we propose to take in detailing this circumstance, which is comparatively little known; and as its interest also recommends it, this furnishes an additional motive. Hypatia was the daughter of Theon, an eminent mathematician of Alexandria, some of whose writings are still extant. By her father she was instructed in the mathematics, and from other great men, who at that period abounded in Alexandria, she learned the Platonic and Aristotelian philosophy, and acquired such a knowledge of these sciences, that she taught them publicly, with the greatest applause. She was young and beautiful, had a personable figure, was sprightly and agreeable in conversation, though, at the same time, modest; and she possessed the most rigid virtue, which was proof against every temptation. She conducted herself with so much propriety towards her lovers, that they never could obtain more than the pleasure of her company, and hearing her discourse; and with this, which they considered as an honour, they were contented. Those who were so daring as to desire further communion she dismissed; and even destroyed the appetite of one of her admirers, who would not suffer her to philosophise, by means of some strong preparation, which others appear not to have since imitated.

She suffered so cruel a death, that had she been a Christian, and suffered from Pagan error, her name would have been ranked among its most honoured victims in the list of martyrology; but being a Pagan, and suffering from the persecution of superstitious and anti-Christian zeal, she is honoured among the foremost of martyrs to celestial philosophy.

The name of the Christian patriarch, at that period in Alexandria, was Cyrill, whose family had, for upwards of a hundred years before his time, produced bishops, who had been much more serviceable to their own family connections than they had ever been towards the propagation of the Christian faith. The present was proud, litigious, and revengeful, vindictive and intolerant to the last degree; his ignorance debasing his own character as a man, and scandalising the religion of which he was so unworthy a minister. He stupidly conceived himself sanctioned in everything which his foolish and mistaken ideas might dictate to be for the glory of God, and acted as a persecutor, prosecutor, judge, and executioner: he had condemned Nestorias without hearing his defence. As the city of Alexandria was then very flourishing on account of its extended commerce, the emperor had there allowed greater toleration and more peculiar privileges to all religions, than in any other place: it consequently contained, among others, a great number of Jews, who carried on a most extensive trade, as well as a great many Pagan families. In the eyes of the bigot Cyrill this was wrong; he would have the sheep-fold clean, and the Jews must be banished. The governor, however, who was a man of prudence and sober discretion, much better acquainted with the real interests of the city, opposed a measure he saw replete with mischief, and even caused to be condemned to death a Christian profligate, who had injured the Jews. This malefactor was, by the express order of Cyrill, buried in the church as a martyr; and he collected an army of five hundred lazy monks, who abused the governor in the public streets, and excited an insurrection among the people against the Jews, so that the debased race of Abraham was expelled from the city where they had so long existed unmolested from the time of Alexander the Great.

Cyrill, one day, whilst looking for objects of persecution, saw a number of carriages, attended with servants, belonging to the first families in the city, before a certain house. Inquiring what was the cause of the assembly, he was informed that it was the habitation of the lovely Hypatia, who, on account of her extensive learning and very eminent talents, was visited by people of the first respectability. This afforded to the malignant priest a sufficient object for the exercise of his jealousy against the meritorious, the unoffending, the beautiful Hypatia. He from that moment resolved upon her destruction. Accordingly he lost no time in exciting his myrmidons, the monks and priests, those who should have been the ministers of that religion which they professed to teach, to destroy the fair philosopher. They accordingly, with diabolical rage, and instigated by infernal cruelty, took the earliest opportunity to seize her, hurried her to the church—the temple of peace and good-will—which they violated by an offence at which humanity must shudder; having torn the clothes from her delicate form, they tore the flesh from her bones with potsherds, then dragged her mangled body about the city, and afterwards burnt it.

This demoniacal tragedy took place in the year 415, and was perpetrated by the professed servants of Him who came into world to save those which were lost—to preach peace and good-will to all men. The impressions which such an event made upon people of every persuasion may be conceived; they admit not of description from a feeble pen: but we may ask the question, was it such a transaction as was calculated to make converts to the doctrines of Christianity?—whose avowed motive and maxim is, in the words of Milton,

All historians are not agreed in some circumstances of the preceding relation; but they generally unite in bestowing praise upon Hypatia, whose memory was long honoured by her grateful and affectionate scholars, among whom was Synesius, of a noble Pagan family, who had cultivated philosophy and the mathematics with the utmost ardour, and who had been one of her most intimate friends and followers. On account of his learning and virtues, many eminent talents, and open disposition, the inhabitants of Ptolemais were desirous he should be bishop, having been previously employed on many public and important concerns with success. After modestly desiring, for a long period, that they would fix their choice upon a more worthy object, they still persisting, he assented, upon condition that he was not to believe in the resurrection, to which he could not at that time bring his internal conviction: he suffered himself to be baptised, and became their bishop; he was confirmed by the orthodox patriarch Theophilus, the predecessor of Cyrill, to whose jurisdiction Ptolemais belonged: he afterwards renounced his error respecting the resurrection. This learned man evinced his gratitude to Hypatia, by the honourable mention which he made of her in some of his writings, still preserved.

In his fifteenth letter to her, he tells Hypatia, that he was so unfortunate, or found himself so ill, that he wished to use an hydroscopium (the Greek for hydrometer), and he requests that she would cause one to be constructed for him. He says, “It is a cylindrical tube, of the size of a reed or pipe; a line is drawn upon it lengthways, which is intersected by others, and these point out the weight of water. At the end of the tube is a cone, the base of which is joined to that of the tube, so that they have both only one base. This part of the instrument is called baryllion. If it be placed in water, it remains in a perpendicular direction, so that one can readily discover by it the weight of the fluid.”

Petau, who published the works of Synesius, in the year 1640, acknowledges that he did not understand this passage. An old scoliast, he says, who had added some illegible words, thought it was a water-clock; but the ellepsydra was not immersed in water, but filled with it. He therefore thought that it might allude to the chorobates, which Vitruvius describes as an instrument employed in levelling; but it appears that Synesius, who complained of ill health, could have no occasion for such an instrument. Besides, no part of that instrument he describes, has any resemblance to the one described by Synesius.

From the works of Fermat, an excellent mathematician, and a very learned man, well acquainted with antiquities and the works of the ancients, we give the following explanation concerning the hydroscopium of Archimedes, as this article would be incomplete without it:—

“It is impossible,” says he, “that the hydroscopium could be the level or chorobates of Vitruvius, for the lines on the latter were perpendicular to the horizon, whereas the lines on the former were parallel to it. The hydroscopium was undoubtedly a hydrometer of the simplest construction. The tube may be made of copper, and open at the top; but at the other end, which, when used, is the lowest, it must terminate with a cone, the base of which is added to that of the tube. Lengthwise, along the tube, are drawn two lines, which are intersected by others, and the more numerous these divisions are, the instrument will be so much the more correct.—When placed in water it sinks to a certain depth, which will be marked by the cross-lines, and which will be greater, according to the lightness of the water.” A figure which is added, might have been dispensed with. When a common friend of Fermat and Petau showed it to the latter, he considered it to be so just, and explanatory of the real meaning of Synesius, that he wished to be allowed the opportunity of introducing it in a new edition of the works of Synesius.

FINIS.

J.S. Pratt, Stokesley, Yorkshire.