Guilford sat as a judge at some of the Popish Plot trials, and like his colleagues he has been accused of excessive credulity in believing the lies of Titus Oates and the other informers. On the other hand, it has been argued that the senior Chief Justice, Sir William Scroggs, so dominated the proceedings that none of the other judges had any influence on the outcome. If North succumbed to the prevailing hysteria, so did many others: his brother Roger wrote that "it was a time when wise men behaved like stark fools". When public opinion finally began to turn against the Plot, the Crown moved against its instigators. North presided at the trial of one of the more disreputable of the Plot informers, Stephen College, nicknamed "the Protestant joiner", for high treason, in August 1681, and virtually ordered the jury to convict him. College was duly found guilty and hanged. North's conduct of the trial attracted a great deal of criticism, as the evidence of treason was considered by many to be flimsy, and the charge had already been thrown out by a grand jury.
Later years
Guilford was hostile to Lord Jeffreys, and regarded the future Lord Chief Justice, Sir Robert Wright, as utterly unfit for any judicial office; he was well qualified to assess Wright's ability since Wright as a young barrister had relied on North to write his legal opinions for him. He has been criticised for remaining in office after Wright was made Chief Justice over his vehement objections, especially as it must have been clear that he no longer had any influence over judicial appointments. On the other hand, he may have felt that keeping Jeffreys out of the Lord Chancellorship was a sufficient justification for clinging to office.
Character
Guilford was generally respected for his integrity,, but he was sometimes accused of self-importance and a lack of any sense of humour; for example he showed excessive agitation at the ridiculous rumour spread by Sunderland and Jeffreys that he had been seen riding on a rhinoceros. Sunderland hated North with a passion, describing him as the most unfit man who ever held his office: "partial, unreasonable, corrupt, arbitrary and ignorant". There is no reason to believe any of these accusations: certainly no one, other than Sunderland, seems to have thought that Guilford was either corrupt or ignorant.
Death
Guilford died, it seems rather unexpectedly, at his country house, Wroxton Abbey, near Banbury, on 5 September 1685, aged only 47. Although he had apparently been suffering from stress and overwork, the precise reasons for his early death are unclear. His rather cryptic last words were: "It will not do".
Like many upper-class Englishmen of his time, North was devoted to music. Less typically for his time and class he had a keen interest in musical theory, and published a book on the subject, A Philosophical essay on musick, which has been praised as "an admirably clear exposition of the physical basis of music". Francis North's musical notations have been described as the earliest known examples of synthetic phonograms.
