OBSERVATION. 21 



character. Similarly no number of failures to obtain a 

 general solution of equations of the fifth degree would 

 establish the impossibility of the task, but in an indirect 

 mode,, equivalent to a reductio ad absurdum, the impossi- 

 bility is considered to be prov'ed b . 



b Peacock, ' Algebra/ vol. ii. p. 359. Serret, ' Algebra Supe'rieure/ 

 2nd ed. p. 289. 



