The Spinning Jenny was used to spin cotton. The device was a frame that held multiple spindles, and allowed the person operating it to spin up to eight spools at once. This number increased as technology advanced.
The Spinning Jenny was created by James Hargreaves, and named after his wife. His machine was an answer to the increase in demand from weavers. The demand had increased when John Kay created the flying shuttle and basically doubled the amount of work they could put out. The Spinning Jenny was the first improvement on the spinning wheel since its invention. The machine was one of the early examples of what is referred to as the mechanical advantage, showing how much work can be accomplished by machines versus man.