The main idea was developed as a machine with eight wooden spindles at one end, spun from a much larger wheel at the other. A set of eight rovings were attached to a beam that could roll. A clamp-like device in the roving beam allowed the operator to then release all the threads at once, to be collected on spools. The flying shuttle had increased yarn demand by the weavers by doubling their productivity, and now the spinning jenny could supply that demand by increasing the spinners' productivity even more. The machines were often operated by children, who could more easily move about them. The machine produced coarse yarn that lacked strength, but it was still suitable for filling out the weft of fabric, using stronger yarn for the warp. Later developments slightly lowered the quality of the yarn, but increased the number of spindles to eighty or more.
James Hargreaves was born in Oswaldtwistle, near Blackburn, in 1720. He received no formal education and was never taught how to read or write. He moved to Stanhill looking for work and raised a family there, working as a spinner and carpenter.
Blackburn was known for the production of Blackburn greys, a type of fabric that combined linen warp and cotton weft. At the time cotton production could not keep up with demand, and Hargreaves spent some time considering how to improve the process. The most common story told about the invention of the device is that his daughter, Jenny, knocked over one of their own spinning wheels. The device kept working as normal, with the spindle now pointed upright. Hargreaves realized there was no particular reason the spindles had to be horizontal, as they always had been, and he could place them vertically in a row.
The name is variously said to derive from the tale above (although Hargreaves did not have a daughter called Jenny); from the daughter of Thomas Highs (another craftsman, who is the possible true inventor of the spinning jenny); or from engine (see also cotton gin).
Eventually Hargreaves applied for a patent on the jenny in July 1770. By this time a number of spinners in Lancashire were already using copies of the machine, and Hargreaves sent notice that he was taking legal action against them. The manufacturers met, and offered Hargreaves £3000. He at first demanded £7000, and at last stood out for £4000, but the case eventually fell apart when it was learned he had already sold several in the past.
The partnership with Barney carried on "with moderate success" until Hargreaves' unfortunate death in April 22 1778. That year Samuel Crompton invented the spinning mule, combining the spinning jenny with Richard Arkwright's spinning frame and again dramatically increasing yarn production.
The spinning jenny was a huge success due to the fact that it could hold more than one ball of yarn, therefore making more clothing materials in a shorter amount of time while reducing the overall cost.