This sparry fluor is found abundantly in Derbyshire, as well as in the mines of Germany. Theophrastus is the first who notices the effect of sparry fluor, by observing that there are certain stones which, when added to silver, copper, and iron ores, become fluid. It appears that Cronstedt was the first systematic writer who gave it a name.
When spiritus nitri per distillationem has passed into the recipient, ply it with a strong fire, and when well dephlegmated, pour it, (as it corrodes ordinary glass,) into a Waldenburg flask; then throw into it a pulverised green Bohemian emerald, otherwise called hesphorus, (which, when reduced to powder and heated, emits in the dark a green light,) and place it in warm sand for twenty-four hours. Take a piece of glass, well cleaned, and freed from all grease by means of a ley; put a border of wax round it, about an inch in height, and cover it equally all over with the above acid. The longer you let it stand, so much the better; and at the end of some time the glass will be corroded, and the figures which have been traced out with sulphur and oil varnish will appear as if raised above the plane of the glass.
HYDROMETERS.
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.