Though suffering much from his usual headaches, which frequently disabled him from thinking, Watt finished the drawings of the rotary engine in a week, and forwarded them to Boulton at Soho. “I believe,” he said in a later letter, “a well-regulated expansive-engine is the _ne plus ultra_ of our art.” But he intimated that a new trouble had come upon him in the shape of another inventor of a steam-engine in which all the distinctive principles of his own invention were embodied. “If he be engine mad,” said Watt, “and if it be agreeable to you, he shall have my share of them, provided he will come to my price. I wish to retire, and eat my cake in peace, but will not go without the cake. All mankind seem to have resolved to rob us. Right or wrong, they _will_ pluck the meal from our mouths.”[226] Boulton, on his next journey to London, called upon the alleged inventor, a Mr. Ewer, and declared to Watt that the invention, so far as it was new, was not worth a farthing, and that all that was good in it was borrowed from their engine. “Though the white marks on your cow or your horse,” said he, “may be changed to black, the cow and horse are not the less your property.” He therefore counselled Watt to relieve himself of all anxiety on this account. Watt replied, “Ewer seems to have a genius more capable of inventing than of prudently examining the merits of his invention. Poets lose half the praise they would otherwise get did they but tell us what they discreetly blot. We must publish a book of blots.” [226] Watt to Boulton, 30th August, 1781. [Illustration: OLD ENGINE-HOUSE AT DALCOATH. [By R. P. Leitch.]] Meanwhile Watt went on inventing, even while he was complaining of his inability to invent, and of the uselessness of inventing. Invention had grown into a habit with him, which he could not restrain. In the very letter in which he wrote “It is of no use inventing--everybody is seizing upon our schemes,” he communicated to Boulton that he had contrived a machine, then erecting at Dalcoath, for the purpose of stopping the engine when at full speed, when any accident happened to the rods or outside chains,--first taking away the power, and then holding the bob fast whenever it might be at the turn.[227] A few days later he communicated that he had contrived a new way of opening the regulators. He was also finishing his plan of the new equalising beam, and the double expansion engine, which he requested might be proceeded with at once. “I have shown the equalising beam,” said he, “to no person whatever. Please push it on. It is our _dernier ressort_, and may perhaps be all that villany will leave us, and that not long.”[228] Boulton wrote back, bidding his partner to be of good heart. “If our spirits don’t fail us,” said he, “I think our engine won’t.”