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:--