Hitting the seam makes it deviate. Backspinners and topspinners are used to fool the batsman with flight. ^What said up there agrees especially Anil Kumble would
The most likelihood is that Barnes bowled two kinds of deliveries off two grips. First one is the orthodox seamer. Since he was a strong man, would have been fast medium with the pace. Other one would have been the leg roller, which is rolled of the back of the hand to get some spin, but bowled with a medium pacers action (poor man's example is Chris Harris). Now this would have been lot slower than his seamer, but it's still possible to be little quicker than an orthodox spinner. Any batsman of substance, would have been able to pick the difference of pace if Barnes bowled the former in high pace. Being a shrewd operator, he would have bowled his seamers little slower, so the change of speed is not apparent. With new ball, he must have bowled close to full speed with swing and seam, with one or two leg rollers to intervene. When ball got older he would have gone to leg roller mode, and with slowed down seamer to make it un-noticable. One in a while he would have let it rip with full pace. I think the cricket vocabulary during Barnes' time was very poor, and what the writers meant with certain phrases may not be the same thing used today
....These days medium pace and spin bowling are two distinct schools, one incompatible with the other. But there has never been a more successful style of bowling than fast-medium spin, as purveyed by Barnes in particular. He was, John Arlott wrote, "a right-arm fast-medium bowler with the accuracy, spin and resource of a slow bowler".
Barnes, "square shouldered as a tailor's model" as Alan Ross put it in his poem, is said to be by men who saw them both to have been around the same speed as Alec Bedser, which suggests he was bowling between 70 and 80mph. These days Swann is reckoned to bowl quickly for a spinner, and his average speed is around 60mph. Barnes's stock delivery was a fast leg break that swerved one way in the air and then span back the other off the pitch. He married this with a fast off break that did the exact reverse, a ball he was taught by the Australian Monty Noble, another early master of spin-swerve bowling. Barnes's particular release meant that the two were difficult to distinguish. He did not unfurl the wrist for his leg break, but rather cocked it backwards and rotated it, as though he was, as Rajan says, "unscrewing a light bulb". If you want a more technical explanation, you can find one in Bob Woolmer's Art and Science of Cricket.
This method brought Barnes 189 Test wickets at 16.43 each, and universal recognition from his contemporaries as the greatest bowler of his era. It was the swerve that did it, movement akin to the drift you still see now in good spin bowling, only faster through the air. But this was genuine spin bowling – Barnes was outraged when David Frith once had the temerity to ask him if he cut the ball? "'Cut it?' He glared, and again I wondered if he might hurl something at me. 'I spun the ball!'" The great Australian batsmen Clem Hill remembered how a "ball pitched outside my leg-stump, safe to the push off my pads, I thought. Before I could 'pick up' my bat, my off-stump was knocked silly".
The Spin | Rejoicing in the Twirlymen and the forgotten art of medium-paced spin | Andy Bull | Sport | guardian.co.uk
He took wickets against Australia and SA. SA played 11 tests before their first win and played their first test in 1879 12 years after Australia and England. SA won their first test match in 1906. So was he really awesome or was there the lack of quality batsman in that era batting with bats with a sweetspot smaller than a squash ball
Shane Warne - Ball Of The Century - YouTube
^ball of the century lol think a few quickies might disagree with that as beating a guy lie Tendulkar or Lara reflexes with pure pace is also a outstanding achievement by itself
And that "ball of the century" is grossly overrated. Warne's ball to Basit Ali and Murali's to Sandagopan Ramesh are bigger jaffas easily.