Watt was very busy at this time in preparing the specification and drawings of the circular motion, which he said he found an extremely difficult job owing to the distracted state of his head. The letters patent for the invention had been secured on the 25th October, 1781, and he had four months allowed him in which to prepare and lodge the full description. He laboured at his work late and early, his mind being for months in the throes of invention. In the beginning of November we find him writing to Boulton, sending him the “first three yards of the specification,” written out on folio sheets joined together. Watt’s letters to his partner at this time contain numerous rough sketches of his proposed methods for securing circular motion without using the crank, from which he conceived himself to be in a measure precluded by Pickard’s patent. He devised no fewer than five distinct methods by which this object might be accomplished, by means of wheels of various sorts rotating round an axis. The method eventually preferred was the one invented by Wm. Murdock, and commonly known as the sun and planet motion.[231] “It has the singular property,” said Watt, “of going twice round for each stroke of the engine, and may be made to go oftener round if required without additional machinery.” [231] Watt, in a letter to Boulton, dated the 3rd July, 1782, speaks of it as an old plan of his own “revived and executed by William Murdock;” but we were informed by the late Mr. Josiah Parkes, that at an interview which he had with Mr. Watt at Heathfield, at which Murdock was present, Murdock spoke of the Sun and Planet motion as his invention, which Watt did not contradict. Boulton also attributed the invention to Murdock, as appears from his letter to Henderson, dated 22nd January, 1782; in which he says,--“Mr. Watt’s packet is not ready. I am to wait till his drawings [of the rotatory motion] are completed, which he is executing himself. There was some informality in those sent from Soho. Besides, he has another rotative scheme to add, which I could have told him of long ago, when first invented by William Murdock, but I did not think it a matter of much consequence.” [Illustration: SUN AND PLANET MOTION.]