In 1940, Les Paul revisited his experiments with the train rail. This time he created a similar prototype instrument, a one-off solid-body electric guitar known as "The Log", which was a length of 4x4 piece of lumber with a bridge, neck, strings, and hand-wound pickup. The Log was built after-hours by Paul at the Epiphone guitar factory, and is one of the first solid-body electric guitars. For the sake of appearance, he attached the body of an Epiphone hollow-body guitar sawn lengthwise with The Log in the middle. This solved his two main problems: feedback, as the acoustic body no longer resonated with the amplified sound, and sustain, as the energy of the strings was not dissipated in generating sound through the guitar body. These instruments were constantly being improved and modified over the years, and Paul continued to use them in his recordings even after the development of his eponymous Gibson model.