472 SIMSON. 



found, but half the second being in the Savilian library 

 at Oxford, was translated by Wallis a century later. 

 Commandini's translation, with his learned commen- 

 tary, was not printed before his death, but the Duke of 

 Urbino (Francesco Maria) caused it to be published 

 in 1588, at Pisa, and a second edition was published 

 at Venice the next year : a fact most honourable to 

 that learned and accomplished age, when we recollect 

 how many years Newton's immortal work was pub- 

 lished before it reached a second edition, and that in 

 the seventeenth and eighteenth centuries. 



The two first books of Pappus appear to have been 

 purely arithmetical, so that their loss is little to be 

 lamented. The eighth is on mechanics, and the other 

 five are geometrical. The most interesting portion is 

 the seventh ; the introduction of which, addressed to 

 his son as a guide of his geometrical studies, contains 

 a full enumeration of the works written by the Greek 

 geometers, and an account of the particular subjects 

 which each treated, in some instances giving a summary 

 of the propositions themselves with more or less ob- 

 scurity, but always with great brevity. Among them 

 was a work which excited great interest, and for a 

 long time baffled the conjectures of mathematicians, 

 Euclid's three books of ' Porisms :' of these we shall 

 afterwards have occasion to speak more fully. His 

 'Loci ad Superficiem,' apparently treating of curves 

 of double curvature, is another, the loss of which was 

 greatly lamented, the more because Pappus has given 

 no account of its contents. This he had done in the 

 case of the ' Loci Plani' of Apollonius. Euclid's four 

 books on conic sections are also lost: but of Apol- 



