'Platforms,' or low tables of frame-work, are placed near the opening made in the ice, with iron slides extending into the water, and a man stands on each side of this slide, armed with an ice-hook. With this hook the ice is caught and by a sudden jerk thrown up the slide' on to the 'platform.' In a cold day everything is speedily covered with ice by the freezing of the water on the platforms, slides, &c., and the enormous blocks of ice, weighing some of them more than two cwt., are hurled along these slippery surfaces, as if they were without weight. Beside this platform, stands a 'sled' of the same height, capable of containing about three tons; which, when loaded, is drawn upon the ice to the front of the store-house. where a large stationary platform of exactly the same height, is ready to receive its load; which, as soon as discharged, is hoisted block by block, into the house.

Forty men and twelve horses will cut and stow away 400 tons a day. In favourable weather 100 men are sometimes employed at once. When a thaw or a fall of rain occurs, it entirely unfits the ice for market, by rendering it opake and porous; and occasionally snow is immediately followed by rain, and that again by frost, forming snow-ice, which is valueless, and must be removed by the 'plane.' The operation of 'planing' is somewhat similar to that of cutting.' A plane gauged to run in the grooves made by the 'marker,' and which shaves the ice to the depth of three inches, is drawn by a horse, until the whole surface of the ice is planed. The chips thus produced are then scraped off; and if the clear ice is not reached, the process is repeated. If this makes the ice too thin for cutting, it is left in statu quo, and a few nights of hard frost will add below as much as has been taken off above. In addition to filling their ice-houses at the lake and in the large towns, the company fill a large number of private ice-houses during the winter, all the ice for these purposes being transported by railway. It will easily be believed, that the expense of providing tools, building houses, furnishing labour, and constructing and keeping up the railway, is very great; but the traffic is so extensive, and the management of the trade so good, that the ice can be furnished, even in England, at a very trifling cost' (it is retailed at twopence per pound).]

1 For the above account of the mode of collecting the ice at Wenham Lake, we are indebted to the Illustrated London News' for May 17, 1845.

161

HYDROMETER.

THIS instrument, called in Latin hydrometrum, hygroscopium, hygrobaroscopium, hydroscopium, areometrum, and baryllion, serves to determine the weight or specific gravity of different fluid masses, by the depth to which it sinks in them.

The laws respecting the comparative specific gravity of fluids and solid bodies immersed in them were discovered by Archimedes, when he tried the well-known experiment, by order of Hiero king of Sicily, to find the content of a golden crown, made for that sovereign. Upon these is founded the construction of the hydrometer; and it is not improbable that Archimedes, who was killed in the year 212 before the Christian æra, was the inventor of it, though no proofs to warrant this conjecture are to be found in the writings of that great man, or in those of any other author.

The oldest mention of the hydrometer occurs in the fifth century, and may be found in the letters of Synesius to Hypatia. Of the lives of these two persons I must here give some anecdotes, as they deserve to be known on account of the singular fate which attended them. Hypatia was the daughter of Theon, a well-known mathematician of Alexandria, some of whose writings are still extant. By her father she was instructed in mathematics, and from other great men, who at that time abounded in Alexandria, she learned the Platonic and Aristotelian philosophy, and acquired such a complete 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 of hearing her discourse; and with this, which they considered as an honour, they were contented. Those who wished to intrude further were dismissed; and she destroyed the appetite of one who would not suffer her to philosophise, by means of some strong preparation, which, as far as I know, remained a secret. She was

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not haptized, and with all her knowledge, adopted the blind superstition of paganism. Had she been a Christian, and suffered a cruel death from heathen persecution, she would have merited a place in the martyrology of the saints: but the case was reversed; for, by the conduct of the Christians towards her, she became entitled to have her name enrolled in the martyrology of the philosophers.

The patriarch of Alexandria, at the time when she lived, was Cyril, whose family for a hundred years before had produced bishops, who were of more service to their relations than to the church. This prelate was a proud, litigious, vindictive and intolerant man, who thought every thing lawful which he conceived to be for the glory of God; and who, as prosecutor and judge, condemned Nestorius without hearing his defence. In the city of Alexandria, which was then very flourishing on account of its commerce, the emperor allowed greater toleration than he imagined could be justified to the clergy in any other place; and it contained a great many Jews, who carried on an extensive trade, as well as a number of pagan families who were of service to the city, or at least did it no harm. This, in the eyes of Cyril, was not proper; he would have the sheep-fold clean, and the Jews must be banished. Orestes, however, the governor, who was a man of prudence, and better acquainted with the interests of the city, opposed a measure that was likely to be attended with mischief, and he even caused to be condemned to death a Christian profligate, who had done some injury to the Jews. This malefactor was, by the order of Cyril, buried in the church as a martyr; and he immediately collected five hundred monks, who ill-treated Orestes in the streets, and excited an insurrection among the people, who plundered the unfortunate Jews, and expelled them from a city in which they had lived since the time of Alexander the Great.

Cyril, observing one day a great number of horses and servants belonging to persons of the first rank, before a certain house in the city, inquired the cause of their being assembled in that manner. He was informed that the house was the habitation of the celebrated female philosopher Hypatia, who, on account of her extensive learning and eminent talents, was visited not only by people of the highest distinction, but even by the governor himself. This was sufficient

to excite the bishop's jealousy against the unbelieving Hypatia, and he resolved to effect her ruin. As he had instigated the people against the Jews, he in like manner encouraged them to attack Hypatia. They seized her in the street, hurried her to the church, stripped off her clothes, tore her flesh to pieces with potsherds, dragged her mangled limbs about through the city, and at length burned them. This bloody tragedy, which took place in the year 415, could tend only to inspire the heathens with a greater hatred to Christianity, and to make sensible Christians ashamed of the conduct of their brethren. To Cyril, however, it occasioned no shame; on the contrary, he endeavoured to divert the emperor from punishing those who had been guilty of so gross a violation of the principles of justice, and in this he was assisted by his numerous adherents and friends. In some circumstances of this relation historians are not agreed, but they all concur in bestowing praise on Hypatia, whose memory was honoured and preserved by her grateful and affectionate scholars'.

Among these was Synesius, of a noble pagan family, who 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, talents, and open disposition, he was universally esteemed, and he had been employed with great success on public occasions of importance. The church at Ptolemais at length wished to have him for their bishop. After much reluctance he accepted the office, but on condition that they should not require him to acknowledge the resurrection of the dead, which he doubted. The people having consented to allow him this indulgence, he suffered himself to be baptized, and became their bishop. He was confirmed by the orthodox patriarch Theophilus, the predecessor of Cyril, to whose jurisdiction Ptolemais belonged; and he afterwards renounced his errors, and declared himself convinced of the truth of the resurrection. This learned man showed his gratitude to Hypatia, by the honourable mention which he made of her in some letters that are still preserved among his writings.

In his fifteenth letter, he tells Hypatia that he was so un

1 A fuller account of Hypatia may be found in Menagii Histor. Mulier. Philosoph. Lugd. 1690; Bruckeri Hist. Crit. Philos. ii. p. 351; and Wolfii Fragmenta Mulierum Græc. Gott. 1739, 4to.

fortunate, or found himself so ill, that he wished to use a hydroscopium, and he requests that she would cause one to be constructed for him. "It is a cylindrical tube," adds he, "of the size of a reed or pipe. A line is drawn upon it lengthwise, 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 discover by it the weight of the fluid."

Petavius, who published the works of Synesius in the year 1640, acknowledges in his annotations, that this passage he did not understand. An old scholiast, he says, who had added some illegible words, seemed to think that it referred to a water-clock; but this he considers improbable, as a clepsydra was not immersed in water, but filled with it. He conjectures, therefore, that it may allude to some such instruinent as that which Vitruvius calls chorobates. The latter however was employed for leveling; and it appears that Synesius, who complains of the bad state of his health, could not think of leveling. Besides, no part of the description in Vitruvius agrees with that which is given in so clear a manner by Synesius.

Petau published his edition of the works of this philosopher in the time of Peter de Fermat, conseiller au parlement de Toulouse, a man of great learning, who was an excellent mathematician, and well-acquainted with antiquities and the works of the ancients. We have by the latter a commentary upon some obscure passages of Athenæus, annotations on the writings of Theon of Smyrna, and emendations from a manuscript to the Stratagemata of Polyænus, which may be found also in his Miscellanies. Mursinna, in his edition of the same author, has added them to the end of the preface. As Fermat was often consulted respecting difficult passages of the ancients, he could not be unacquainted with that in the new edition of Synesius. He drew up an explanation of it, and gave it to a friend who was then about to publish a French translation of Bened. Castelli's book, Della Misura dell' Acque Correnti, and who caused it to be printed along with that work. Fermat died in the year 1665. After his death his