Rough sketches of these various methods were forwarded to Soho in order that the requisite careful drawings of them might be prepared in time to be lodged with the specification; but when they reached Watt in Cornwall, he declared them to be so clumsily executed that he could not for very shame send them in; and though greatly pressed by mining business, and suffering from “backache, headache, and lowness of spirits,” he set to work to copy them with his own hands. He worked up his spare time so diligently, that in ten days he had the plans finished and returned to Boulton, whom he wrote saying that he had improved the construction of several of the machines, and “got one copy of the specification drawing finished in an elegant manner upon vellum, being the neatest drawing he had ever made.”[232] The necessary measures being then taken to perfect the patent, it was duly enrolled on the 23rd February, 1782. During the time that Watt was busy completing the above specification and drawings, his mind was full of other projects, one of which was the perfecting of his new expansive engine.[233] It is curious to find him, in his letters to Boulton, anticipating the plan of superheating the steam before entering the cylinders, which has since been carried into effect with so much success. [232] Watt to Boulton, 26th Jan., 1782. [233] “I have some time ago thought,” wrote Watt, “of a new expansive engine--a reciprocating engine with a heavy circular fly moved by a pinion from the end of the beam, so as to make three turns per down-stroke and as many contrariwise per return; so that in the first half of the stroke it may acquire a momentum which will carry it through the last half; and if a weight equal to half the load be put upon the inner end of the beam, and the engine be made to lift it during the return, by making a vacuum above the piston and using a rack instead of a chain, a cylinder of the present size may work to the same depth by half the steam; and I believe the engine will work very sweetly.”--Watt to Boulton, 16th January, 1782.