SIMSON. 145 



earlier, the obscure subject of Porisms had engaged 

 his thoughts ; and soon after, his mind was so entirely 

 absorbed by it that he could apply to no other investi- 

 gation. The extreme imperfection of the text of Pappus, 

 the dubious nature of his description, his rejection of 

 the definition which appeared intelligible, his substi- 

 tuting nothing in its place except an account so general 

 that it really conveyed no precise information, the 

 hiatus in the account which he subjoins of Euclid's 

 three books, so that even with the help of the lemmas 

 related to these propositions of the lost work, no clear 

 or steady light could be descried to guide the inquirer 

 for the first porism of the first book alone remained 

 entire, the general porism being given wholly truncated 

 (mancum et imperfectum) all seemed to present 

 obstacles wholly insurmountable, and after various 

 attempts for years he was fain to conclude with Halley 

 that the mystery belonged to the number of those which 

 can never be penetrated. He lost his rest in the anxiety 

 of this inquiry ; sleep forsook his couch, his appetite 

 was gone ; his health was wholly shaken ; he was com- 

 pelled to give over the pursuit ; he was " obliged," he 

 says, " to resolve steadily that he never more should 

 touch the subject, and as often as it came upon him he 

 drove it away from his thoughts."* 



It happened, however, about the month of April, 

 1722, that while walking on the banks of the Clyde 

 with some friends, he had fallen behind the company ; 

 and musing alone, the rejected topic found access to 

 his thoughts. After some time a sudden light broke 

 in upon him ; it seemed at length as if he could descry 

 something of a path, slippery, tangled, interrupted, but 

 still practicable, and leading at least in the direction 

 towards the object of his research. He eagerly drew 

 a figure on the stump of a neighbouring tree with a 



* " Firmiter animum induxi haec nunqnam in posterum investigare. 

 Uncle quoties menti occuirebant, toties eas arcebam." (Op. Eel. 320. 

 Prajf. ad Forismata.) 



L 



