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 proved b . 



l Peacock, ' Algebra,' vol. ii. p. 359. Serret, ' Algebra Superieure/ 

 2nd ed. p. 289. 



