324

HYDROMETERS).

Petau, who published the works of Synesius, in the year1640, acknowledges in his annotations that he did notunderstand this passage. An old scholiast, he says, whohad added some illegible words, thought it was a water-clock ; but the clepsijdra was not immersed in water, butfilled with it. He therefore conjectured that it might allude tothe chorobales, which Vitruvius describes as an instrumentto be employed in levelling; but it appears that Synesius,who complained of ill health, could have no occasion forsuch an instrument. Besides, no part of that instrumenthe describes, has any resemblance to the one described bySynesius.

Petau published his edition of the w r orks of this philo-sopher, in the time of Peter de Fermat, conseiller au parle-nient de Toulouse, an excellent mathematician, and a verylearned man, well acquainted with antiquities and the worksof the ancients. By him there is a learned commentaryupon some obscure passages of Athenmus, annotations onthe writings of Theou of Smyrna, and annotations upona manuscript of the Slratayemata of Poly senus, which may befound in his Miscellanies. Mursinna, in his edition of thesame author, has added them to the end of his preface.As Fermat was often consulted on difficult passages of theancients, he could not have been unacquainted with that inthe new edition of Synesius ; he accordingly explained itin a written description, which he gave to a friend, bywhom it was published in Bened. Castelli’s book DellaMisura dell' Acque correnti. Fermat died anno 1665; sub-sequent to his death his son published some of his posthu-mous writings, under the title of Varia Opera Mathematica ;*in which collection appears the above treatise on the hy-droscopium.

From this work of Fermat, the following explanationconcerning the hydroscopium of Archimedes, and the choro-

ai/TOV ck &anpou xom ? Kara itm* tyxu/xiyo; oorr* etrai xwnv 0atrir rou

Kwvoy t t aat rov tf-twXuroff. Auto touto ijti to BapuXTuev. OTar our etcitafln? tov suXov, ofSoc tTrn^ti xai 7 rapefei rst to? x«t arofxat api9/tt£iv* at t»c

pomie tt 0 *t yvwptr/uara. £0 sum infortunii redactus, ul hjdroscopio opus habeam ;jube mihi labricari ac coenti. Tubului est cyltndri figurant habeas, tibiie magiti-tudine forma. Hie in una recta lmea incisiones habet, quibus aquarum libramen-turn cognoscimus Obturat enint ilium altera ex parte conus, ?equaBili posituinsertus, ita ut communis sit aniborunt basis, com videlicet atque tubuli. HocIpsuin est, quod Bar^lliura appellant Jam cam tubulum in aquant deposueris,crectus subit, ut in eo incisiones facile numerare possis, ex quibus libraiuentumcognoscitur.

4 Varia Opera Mathematica D. Petri de Fermat, senatoris Tolosani. Accesse-runt qutedam ejusdem episiul®. Tolosre, 1679, 210 pages folio.