Harris and Bennett moved in similar literary circles but did not actually meet until the relatively late date of 1908, after Harris had written a letter to 'Jacob Tonson' - Bennett's pseudonym for his literary criticism in the New Age. Their friendship would not last long, but for a time they had a deep mutual admiration.
Sources for this page are, predominantly, Frank Harris to Arnold Bennett (1936), a privately-printed pamphlet, which reproduces 58 letters from Harris to Bennett, and Letters of Arnold Bennett, Vol II (1968), which includes 6 letters from Bennett to Harris, as well as several letters to others in which Harris is mentioned.
Arnold Bennett, under his pseudonym of 'Jacob Tonson' had been writing glowing reviews of Harris' work   in the New Age. (The original Tonson was an eighteenth century publisher of - amongst others - Dryden's poetry and the first edition of Paradise Lost). Harris wrote to 'Tonson' about The Bomb and was pleasantly surprised to receive a reply from Bennett which included the statement that "there is no author in England whom I should more like to meet than the author of Montes" (referring to Harris' great short story, Montes, the Matador). Bennett was by this time an established novelist: Harris must surely have been flattered by his praise.
The two men, with their wives, met at Bennett's house in Paris. Harris and Bennett were decidedly of very different temperaments. Bennett was a natural writer to whom literary composition came easily, a good-natured and amiable man, a Fabian socialist; Harris found writing hard - surprisingly so, considering the size of his output - and was an agitated, forceful individual, politically inconsistent but given to outbursts of radicalism. Both possessed large egos, Bennett although inclined to shyness being comfortably sure of his own ability, while Harris, outwardly blustering and assertive, was yet deeply insecure. Despite these differences each at this time enjoyed the other's company and works.
Bennett was one of the first to read The Man Shakespeare, a work which he admired greatly - at first almost unreservedly, though with time he would come to recognise some flaws in it. He also read Harris' play Shakespeare and his Love, about which he was less enthusiastic though he couched his criticism tactfully: "the play is as a whole too subtle", he said. On the other hand, The Bomb, he felt, was a great novel marred only by some roughness of construction.
Meanwhile, Frank Harris had been reading The Old Wives' Tale, still reckoned as one of Bennett's finest works. His opinion was that it was a masterpiece until "half way through", that Sophia should have become a prostitute rather than a "lodging house drudge", whose "noble spirit" is "quench[ed] ... in petty economies". Bennett responded that although "in certain moods" he agreed with Frank's criticism, he felt that as "a fully equipped artist" he should be able to "take a Pentonville omnibus and show it to be fine". In other words, he felt confident enough to write about undramatic incidents.
Bennett gave a generally favourable view of an early version of Unpath'd Waters that Harris had sent him. Ever the craftsman, he felt that in some passages greater realism of detail would help to create the illusion striven for, to which Harris answered that he was more concerned with the moral to be imparted and was "indifferent to extreme verisimilitude". But he thanked Bennett for his constructive criticism which he said was unique amongst English critics, illustrating his low opinion of that breed in general by the following story:-
A great nobleman had a celebrated landscape painter to stay with him and asked him to paint some views in the park. The painter had paid no attention to the very beautiful chatelaine who was prepared to admire his work if he admired her. Accompanied by her little son she tripped across the park to him. The painter gives her a curt good-day and goes on with his work. She looks at it for a moment and then exclaims, "Oh Mr. ---- Don't you think you might bring in one of those cows there into the middle distance? They are my husband's Alderneys, you know: it would add just a touch of local colour". The artist looks at her & says nothing -- "Oh, mother," cries the little boy, plucking her by the sleeve, "not a cow! Tell him to put in a lion"!
Doubtless contrary to his intention, this story reminds me of Harris' own criticism of The Old Wives' Tale which surely has something of the little boy in it.
Publishers and other Nuisances
Much of Harris and Bennett's correspondence - that part of it we have - was taken up with discussion of who would publish Harris' work. Bennett suggested that Ford Madox Hueffer (known to posterity as Ford Madox Ford) might print some of his short stories in The English Review, but Hueffer was rather sniffy about them. Harris' conclusion was that Hueffer was "an ass".
Duckworth was recommended as another possibility, for The Man Shakespeare, but that came to naught. Better luck would be had with the American, Mitchell Kennerly, who - despite a certain reluctance to part with money - was to be the publisher of most of Harris' later works in the U.S. A less happy relationship was that with Frank Palmer, whom Bennett had recommended to Harris, the publisher of the English edition of Shakespeare and his Love - according to Harris the "worst of his tribe", both miserly about payment and reluctant to accept Harris' corrections - or his complaints.
Harris also griped that Professor A. C. Bradley had lifted without acknowledgment ideas from Harris' essays on Shakespeare, but despite these plagiarisms his work was still "putrid".
The other great nuisance was Harris' health, always one of his favourite topics. The 'flue' (sic) confined him to his bed, where he complained of having nothing to read - would Bennett send him a copy of his latest book?
Bennett sent his last known letter to Harris in 1912. They would have no further communication as friends. What started the rift is not known, but it was the coming of the First World War that made enemies of them.
In 1914 Harris was declared bankrupt, and skipped to France to escape his creditors. He had just completed a prison sentence for contempt of court, so he had reasons enough for a dislike of England. On the invasion of France by German forces he sailed to America, where he wrote a book England or Germany?, which was somewhat inaccurately described in the British press as espousing the German cause, resulting in a patriotic fervour against him in which Arnold Bennett was a major actor. Bennett even re-edited a volume compiling his New Age articles to expunge any praise of the traitor, Harris.
Both men would die in the same year, 1931, without ever reconciling their differences. Bennett is a conspicuous omission from the Contemporary Portraits and is mentioned briefly in My Life and Loves only for his appreciation of The Man Shakespeare.